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<html>
<head>
<title>KInterbasDB Usage Guide</title>
<link rel="stylesheet" href="global.css" type="text/css">
</head>
<body>
<a href="index.html">Overall Table of Contents</a>
<hr>
<a name="top"><h1 class="compactHeading">KInterbasDB Usage Guide</h1></a>
<a name="toc"><h3>Contents</h3></a>
<ul>
<li><a href="#introduction">Introduction</a>
<br><br>
</li>
<li><a href="#db_api_compliance">Python Database API 2.0 Compliance</a>
<ul>
<li><a href="#db_api_incompatibilities">Incompatibilities</a></li>
<li><a href="#db_api_optional_unsupported">Unsupported Optional Features</a></li>
<li><a href="#db_api_optional_nominally_supported">Nominally Supported Optional Features</a></li>
<li><a href="#db_api_extensions_and_caveats">Extensions and Caveats</a></li>
</ul>
<br>
</li>
<li><a href="#tutorial">Brief Tutorial</a>
<ul>
<li><a href="#tutorial_connect">Connecting to a Database</a></li>
<li><a href="#tutorial_execute_sql">Executing SQL Statements (and Retrieving Results)</a></li>
<li><a href="#tutorial_stored_procedures">Calling Stored Procedures</a></li>
</ul>
<br>
</li>
<li><a href="#adv">Native Database Engine Features and Extensions Beyond the Python DB API</a>
<ul>
<li><a href="#adv_db_creation_deletion">Programmatic Database Creation and Deletion</a></li>
<li><a href="#adv_event">Database Event Notification</a></li>
<li><a href="#adv_trans_control">Advanced Transaction Control</a>
<ul>
<li><a href="#adv_trans_control_parameters">Transaction Parameters</a></li>
<li><a href="#adv_trans_control_retaining">Retaining Operations</a></li>
<li><a href="#adv_trans_control_savepoints">Savepoints</a></li>
<li><a href="#adv_trans_control_distributed">Distributed Transactions</a></li>
</ul>
</li>
<li><a href="#adv_param_conv">Parameter Conversion</a>
<ul>
<li><a href="#adv_param_conv_implicit_from_string">Implicit Conversion of Input Parameters from Strings</a></li>
<li><a href="#adv_param_conv_dynamic_type_translation">Dynamic Type Translation</a></li>
<li><a href="#adv_param_conv_database_arrays">Database Arrays</a></li>
</ul>
</li>
<li><a href="#adv_named_cursors">Named Cursors</a></li>
<li><a href="#adv_prog_maint">Programmatic Server, Database, and User Maintenance</a>
<ul>
<li><a href="#adv_prog_maint_servapi">Services API</a>
<ul>
<li><a href="#adv_prog_maint_servapi_connect">Establishing Services API Connections</a></li>
<li><a href="#adv_prog_maint_servapi_server_config">Querying Server Configuration and Activity Levels</a></li>
<li><a href="#adv_prog_maint_servapi_database_stats">Querying Database Statistics</a></li>
<li><a href="#adv_prog_maint_servapi_backup_restore">Backup and Restoration</a></li>
<li><a href="#adv_prog_maint_servapi_database_maint">Controlling Database Operating Modes, Sweeps, and Repair</a></li>
<li><a href="#adv_prog_maint_servapi_users">User Maintenance</a></li>
</ul>
</li>
<li><a href="#adv_prog_maint_database_info">The <code>database_info</code> Method</a></li>
</ul>
</li>
</ul>
<br>
</li>
<li><a href="#faq_fep">Frequently Asked Questions and Frequently Encountered Pitfalls</a>
<ul>
<li><a href="#faq_fep_result_set_fields_by_name">Refer to Result Row Fields by Name Rather than Index</a></li>
<li><a href="#faq_fep_fixed_point_precise">Precise Fixed Point (<code>NUMERIC</code>/<code>DECIMAL</code>) Handling</a></li>
<li><a href="#faq_fep_datetime">Dates and Times: egenix <code>mx.DateTime</code> vs. Python 2.3+ standard library <code>datetime</code></a></li>
<li><a href="#faq_fep_unicode">Unicode Fields and KInterbasDB</a></li>
<li><a href="#faq_fep_embedded_using_with">Using KInterbasDB with Embedded Firebird</a></li>
<li><a href="#faq_fep_zope_using_with">Using KInterbasDB with Zope</a></li>
<li><a href="#faq_fep_services_api_classic_embedded">Services API on the Classic and Embedded Server Architectures</a></li>
</ul>
<br>
</li>
<li><a href="#references">References (external links)</a></li>
<li><a href="#feedback">Feedback</a><br><br></li>
</ul>
<hr>
<a name="introduction">
<span style="font-size: 175%; font-weight: bold;">Introduction</span>
<span style="font-size: 90%; text-decoration: line-through;">(Propaganda)</span>
</a>
<p class="textParagraph" style="margin-top: 1em;">
The <a href="http://firebirdsql.org">Firebird</a> relational database engine
has a large feature set,
conforms closely to SQL standards,
and is flexible enough to operate either as a standalone server or
as an embedded library on diverse platforms.
In spite of this versatility, the database is exceptionally easy to
use--almost self-managing.
</p>
<p class="textParagraph" style="margin-bottom: 3px;">
The <a href="http://python.org">Python</a> programming language
supports numerous paradigms,
is suitable for constructing both very small and very large programs,
and integrates well with native C and C++ libraries.
Despite the versatility of the language, well written Python code achieves an
almost astonishing lucidity that has led some to call the language
"executable pseudocode".
Noted author and teacher
<a href="http://www.bruceeckel.com">Bruce Eckel</a> has
<a href="http://www.ddj.com/documents/s=876/ddj0050e/0050e.htm">praised</a>
Python as
</p>
<blockquote style="margin-top: 0px;">
"the most efficient language I've ever used. It's 10 times better than any
of the other tools I have used. It's free, it's object-oriented, it adapts
to everything, it runs on everything. There is almost an indescribable,
'quality without a name' attraction on my part."
</blockquote>
<p class="textParagraph">
These two top-flight software tools intersect in a library named KInterbasDB.
KInterbasDB implements Python's standard
<a href="Python-DB-API-2.0.html">Database API 2.0</a>,
but also extends far beyond, to cover Firebird's entire native client API.
KInterbasDB strives to deliver the power of Firebird into the hands of the
Python programmer without compromising the qualities of either tool.
</p>
<p class="textParagraph">
This Usage Guide is not a tutorial on Python, SQL, or Firebird; rather, it
is a topical presentation of KInterbasDB's feature set, with example code
to demonstrate basic usage patterns.
This guide is meant to be consumed in conjunction with the
<a href="Python-DB-API-2.0.html">Python Database API Specification</a>
and the
<a href="#ref_fb_docs_directory">Firebird documentation</a>, especially the
professional, seven-volume
<a href="#ref_ib6_docs">manual</a>
for Firebird's commercial ancestor, Interbase®.
</p>
<p class="textParagraph">
The <a href="#toc">table of contents</a> presents a structural overview
of this document.
</p>
<br>
<hr>
<br>
<a name="db_api_compliance"><h2>Python Database API 2.0 Compliance</h2></a>
<a name="db_api_incompatibilities"><h3>Incompatibilities</h3></a>
<ul>
<li><code>DATETIME</code> type comparison singleton
<p class="textParagraph">
KInterbasDB's deferred loading of dynamic type translators causes this
singleton to behave in violation of the standard until the
<code>kinterbasdb.init</code> function has been called (whether
explicitly or implicitly).
</p>
<p class="textParagraph">
For more information, see
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading_backcompat">this section</a>.
</p>
</li>
</ul>
<a name="db_api_optional_unsupported"><h3>Unsupported Optional Features</h3></a>
<ul>
<li><code>Cursor</code> class
<ul>
<li><code>nextset</code> method<br>
<p class="textParagraph">
This method is not implemented because the database engine does
not support opening multiple result sets simultaneously
with a single cursor.
</p>
<br>
</li>
</ul>
</li>
</ul>
<a name="db_api_optional_nominally_supported"><h3>Nominally Supported Optional Features</h3></a>
<ul>
<li><code>Cursor</code> class
<ul>
<li><code>arraysize</code> attribute<br>
<p class="textParagraph">
As required by the spec, the value of this attribute
is observed with respect to the <code>fetchmany</code>
method. However, changing the value of this attribute does
not make any difference in fetch efficiency because the
database engine only supports fetching a single row at a time.
</p>
<br>
</li>
<li><code>setinputsizes</code> method<br>
<p class="textParagraph">
Although this method is present, it does nothing, as allowed
by the spec.
</p>
<br>
</li>
<li><code>setoutputsize</code> method<br>
<p class="textParagraph">
Although this method is present, it does nothing, as allowed
by the spec.
</p>
</li>
</ul>
</li>
</ul>
<a name="db_api_extensions_and_caveats"><h3>Extensions and Caveats</h3></a>
<p class="textParagraph">
KInterbasDB offers a large feature set beyond the minimal requirements of
the Python DB API.
Most of these extensions are documented in the section of this document
entitled
<a href="#adv">Native Database Engine Features and Extensions Beyond the Python DB API</a>.
</p>
<p class="textParagraph">
This section attempts to document only those features that overlap with
the DB API, or are too insignificant to warrant their own subsection
elsewhere.
</p>
<ul>
<li><code>connect</code> function
<p class="textParagraph">
This function supports the following optional keyword arguments in
addition to those required by the spec:
<ul>
<li><code>role</code> -
for connecting to a database with a specific SQL role
(see page 92 of the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a>
for a discussion of Interbase® roles).
<p class="textParagraph" style="margin-bottom: 0px;">
Example:
</p>
<pre style="margin-top: 0px;">
kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'host:/path/database.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'limited_user'</FONT>,
password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>, <strong>role</strong>=<FONT COLOR="#8f8c47">'MORE_POWERFUL_ROLE'</FONT>)
</pre>
</li>
<li><code>charset</code> -
for explicitly specifying the character set of the connection.
See page 221 of the
<a href="#ref_ib6_docs">Interbase® 6 Data Definition Guide</a>
for a list of available character sets, and
<a href="#faq_fep_unicode">this FAQ</a>
for information on handling extended character sets with KInterbasDB.
<p class="textParagraph" style="margin-bottom: 0px;">
Example:
</p>
<pre style="margin-top: 0px;">
kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'host:/path/database.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>,
password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>, <strong>charset</strong><FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'UNICODE_FSS'</FONT>)
</pre>
</li>
<li><code>dialect</code> -
for explicitly specifying the SQL dialect of the connection.
<p class="textParagraph">
In KInterbasDB 2.x, the default dialect was <code>1</code>
(the compatibility dialect for Interbase® 5.5 and earlier).
In KInterbasDB 3.x, the default dialect is <code>3</code>
(the most featureful dialect, ideal for Interbase® 6.0+
and Firebird).
If you want to connect to Interbase® 5.5 or earlier, you must
explicitly set this argument's value to <code>1</code>.
Dialect <code>2</code> is a transitional dialect that is
normally used only during ports from IB < 6 to IB >= 6 or
Firebird.
</p>
<p class="textParagraph" style="margin-bottom: 0px;">
Example:
</p>
<pre style="margin-top: 0px;">
kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'host:/path/database.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>,
password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>, <strong>dialect</strong><FONT COLOR="#7d0000">=</FONT><FONT COLOR="#666600">1</FONT>)
</pre>
</li>
</ul>
</li>
<li style="margin-top: 1em;"><code>Connection</code> class
<ul>
<li style="margin-bottom: 1em;"><code>charset</code> attribute <em>(read-only)</em><br>
<p class="textParagraph">
The character set of the connection (set via the <code>charset</code>
parameter of <code>kinterbasdb.connect</code>).
</p>
<p class="textParagraph">
See page 221 of the
<a href="#ref_ib6_docs">Interbase® 6 Data Definition Guide</a>
for a list of available character sets, and
<a href="#faq_fep_unicode">this FAQ</a>
for information on handling extended character sets with KInterbasDB.
</p>
</li>
<li style="margin-bottom: 1em;"><code>dialect</code> attribute<br>
<p class="textParagraph">
This integer attribute indicates which SQL dialect the connection
is using.
</p>
<p class="textParagraph">
You should not change a connection's dialect; instead, discard the
connection and establish a new one with the desired dialect.
</p>
<p class="textParagraph">
For more information, see the documentation of the
<code>dialect</code> argument of the
<code>connect</code> function.
</p>
</li>
<li><code>server_version</code> attribute <em>(read-only)</em><br>
<p class="textParagraph">
The version string of the database server
to which this connection is connected.
</p>
<p class="textParagraph">
For example, a connection to Firebird 1.0 on Windows has the
following <code>server_version</code>:<br>
<code>WI-V6.2.794 Firebird 1.0</code>
</p>
<br>
</li>
<li><code>execute_immediate</code> method<br>
<p class="textParagraph">
Executes a statement without caching its prepared form. The statement
must <em>not</em> be of a type that returns a result set.
</p>
<p class="textParagraph">
In most cases
(especially cases in which the same statement--perhaps a parameterized
statement--is executed repeatedly), it is better to create a cursor
using the connection's <code>cursor</code> method, then execute the statement
using one of the cursor's execute methods.
</p>
<p style="margin-bottom: 0px;">
Arguments:
</p>
<ul>
<li>
<code>sql</code> -
string containing the SQL statement to execute.<br>
</li>
</ul>
<br>
</li>
<li style="margin-bottom: 1em;">
<a name="db_api_extensions_and_caveats_precision_mode">
<code>precision_mode</code> attribute
</a><br>
<p class="textParagraph">
Although this attribute is present in KInterbasDB 3.1 and works
in a backward-compatible fashion, it is deprecated in favor of
the more general
<a href="#adv_param_conv_dynamic_type_translation">dynamic type translation</a>
feature.
</p>
</li>
<li><code>commit</code> and <code>rollback</code> methods<br>
<p class="textParagraph">
The <code>commit</code> and <code>rollback</code> methods
accept an optional boolean parameter <code>retaining</code>
(default <code>False</code>) that indicates whether the transactional
context of the transaction being resolved should be recycled.
For details, see the
<a href="#adv_trans_control_retaining">Advanced Transaction Control: Retaining Operations</a>
section of this document.
</p>
<p class="textParagraph">
The <code>rollback</code> method accepts an optional string parameter
<code>savepoint</code> that causes the transaction to roll back only
as far as the designated savepoint, rather than rolling back entirely.
For details, see the
<a href="#adv_trans_control_savepoints">Advanced Transaction Control: Savepoints</a>
section of this document.
</p>
</li>
</ul>
</li>
<li style="margin-top: 1em;"><code>Cursor</code> class
<ul>
<li><code>description</code> attribute<br>
<p class="textParagraph">
KInterbasDB makes <strong>absolutely no guarantees</strong> about
<code>description</code> <strong>except</strong>
those required by the Python Database API Specification 2.0 (that
is, <code>description</code> is
either <code>None</code> or a sequence of 7-element sequences).
Therefore, client programmers should <em>not</em> rely on
<code>description</code> being an instance of a particular class or
type.
<br><br>
</p>
<p class="textParagraph">
KInterbasDB provides several named positional constants to be
used as indices into a given element of <code>description</code> .
The contents of all <code>description</code> elements are defined by
the DB API spec; these constants are provided merely for
convenience.
</p>
<pre>DESCRIPTION_NAME
DESCRIPTION_TYPE_CODE
DESCRIPTION_DISPLAY_SIZE
DESCRIPTION_INTERNAL_SIZE
DESCRIPTION_PRECISION
DESCRIPTION_SCALE
DESCRIPTION_NULL_OK</pre>
<p class="textParagraph">
Here is an example of accessing the <em>name</em> of the first
field in the <code>description</code> of cursor <code>cur</code>:
</p>
<pre class="codeBlock" style="margin-top: 0px;">nameOfFirstField <FONT COLOR="#7d0000">=</FONT> cur.description[<FONT COLOR="#666600">0</FONT>][kinterbasdb.DESCRIPTION_NAME]</pre>
<br>
</li>
<li><code>rowcount</code> attribute<br>
<p class="textParagraph">
Although KInterbasDB's <code>Cursor</code>s implement this attribute, the database
engine's own support for the determination of "rows affected"/"rows
selected" is quirky.
</p>
<p class="textParagraph">
The database engine only supports the determination of rowcount for
<code>INSERT</code>, <code>UPDATE</code>, <code>DELETE</code>, and
<code>SELECT</code> statements.
When stored procedures become involved, row count figures are usually
not available to the client.
</p>
<p class="textParagraph">
Determining rowcount for <code>SELECT</code> statements is
problematic:
the rowcount is reported as zero until at least one row has been
fetched from the result set,
and the rowcount is misreported if the result set is larger than
1302 rows. The server apparently marshals result sets internally
in batches of
1302, and will misreport the rowcount for result sets larger
than 1302 rows until the 1303rd row is fetched, result sets larger
than 2604 rows until the 2605th row is fetched, and so on,
in increments of 1302.
</p>
<p class="textParagraph">
As required by the Python DB API Spec, the rowcount attribute
"is -1 in case no executeXX() has been performed on the cursor or
the rowcount of the last operation is not determinable by the
interface".
</p>
<br>
</li>
<li><code>fetch*</code> methods<br>
<p class="textParagraph">
KInterbasDB makes <strong>absolutely no guarantees</strong>
about the return value of the
<code>fetchone</code> / <code>fetchmany</code> / <code>fetchall</code>
methods <strong>except</strong> that it is a sequence indexed by
field position.
</p>
<p class="textParagraph">
KInterbasDB makes <strong>absolutely no guarantees</strong>
about the return value of the
<code>fetchonemap</code> / <code>fetchmanymap</code> / <code>fetchallmap</code>
methods (documented below)
<strong>except</strong> that it is a mapping of field name to field
value.
</p>
<p class="textParagraph">
Therefore, client programmers should <em>not</em> rely on the return value being
an instance of a particular class or type.
</p>
<br>
</li>
<li>
<a name="db_api_extensions_and_caveats_cursor_fetchonemap">
<code>fetchonemap</code> method<br>
</a>
<p class="textParagraph">
This method is just like the standard <code>fetchone</code> method
of the DB API, except that it returns a mapping of field name to
field value, rather than a sequence.
<br><br>
</p>
</li>
<li><code>fetchmanymap</code> method<br>
<p class="textParagraph">
This method is just like the standard <code>fetchmany</code> method
of the DB API, except that it returns a sequence of mappings of
field name to field value, rather than a sequence of sequences.
<br><br>
</p>
</li>
<li><code>fetchallmap</code> method<br>
<p class="textParagraph">
This method is just like the standard <code>fetchall</code> method
of the DB API, except that it returns a sequence of mappings
of field name to field value, rather than a sequence of sequences.
<br><br>
</p>
</li>
<li><code>iter</code>/<code>itermap</code> methods<br>
<p class="textParagraph">
These methods are equivalent to the
<code>fetchall</code> and <code>fetchallmap</code> methods,
respectively, except that they return iterators rather than
materialized sequences.
</p>
<p class="textParagraph">
<code>iter</code> and <code>itermap</code> are exercised in
<a href="#tutorial_executing_example_2">this example</a>.
</p>
<br><br>
</li>
</ul>
</li>
</ul>
<hr>
<a name="tutorial"><h2>Tutorial</h2></a>
<p class="textParagraph">
This brief tutorial aims to get the reader started by
demonstrating elementary usage of KInterbasDB. It
is not a comprehensive Python Database API tutorial, nor is it
comprehensive in its coverage of anything else.
</p>
<p class="textParagraph">
The numerous advanced features of KInterbasDB are covered in
<a href="#adv">another section</a> of this document, which is not in a
tutorial format, though it is replete with examples.
</p>
<a name="tutorial_connect"><h3>Connecting to a Database</h3></a>
<a name="tutorial_connecting_example_1"><h4>Example 1</h4>
<p class="textParagraph">
A database connection is typically established with code such as this:
</p>
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
<FONT COLOR="#32a532"># The server is named 'bison'; the database file is at '/temp/test.db'.</FONT>
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
<FONT COLOR="#32a532"># Or, equivalently:</FONT>
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(
host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison'</FONT>, database<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'/temp/test.db'</FONT>,
user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>
)
</PRE>
</pre>
<a name="tutorial_connecting_example_2"><h4>Example 2</h4></a>
<p class="textParagraph">
Suppose we want to connect to an Interbase® 5.5 server, specifying UNICODE_FSS
as the character set of the connection:
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(
dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>,
user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>,
dialect<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#666600">1</FONT>, <FONT COLOR="#32a532"># necessary for Interbase® < 6.0</FONT>
charset<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'UNICODE_FSS'</FONT> <FONT COLOR="#32a532"># specify a character set for the connection</FONT>
)
</pre>
</p>
<br>
<a name="tutorial_execute_sql"><h3>Executing SQL Statements</h3></a>
<p class="textParagraph">
For this section, suppose we have a table defined and populated by the
following SQL code:
</p>
<pre class="codeBlock"><FONT COLOR="#0000ff">create</FONT> <FONT COLOR="#0000ff">table</FONT> people
(
name_last <FONT COLOR="#0000ff">varchar</FONT>(<FONT COLOR="#666600">20</FONT>),
age <FONT COLOR="#0000ff">integer</FONT>
);
<FONT COLOR="#0000ff">insert</FONT> <FONT COLOR="#0000ff">into</FONT> people (name_last, age) <FONT COLOR="#0000ff">values</FONT> (<FONT COLOR="#8f8c47">'Yeltsin'</FONT>, <FONT COLOR="#666600">72</FONT>);
<FONT COLOR="#0000ff">insert</FONT> <FONT COLOR="#0000ff">into</FONT> people (name_last, age) <FONT COLOR="#0000ff">values</FONT> (<FONT COLOR="#8f8c47">'Putin'</FONT>, <FONT COLOR="#666600">51</FONT>);
</pre>
<a name="tutorial_executing_example_1"><h4>Example 1</h4></a>
<p class="textParagraph">
This example shows the <em>simplest</em> way to
print the entire contents of the <code>people</code> table:
</p>
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(
dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>,
user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>
)
<FONT COLOR="#32a532"># Get a Cursor object that operates in the context of Connection con:</FONT>
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
<FONT COLOR="#32a532"># Execute the SELECT statement:</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from people order by age"</FONT>)
<FONT COLOR="#32a532"># Retrieve all rows as a sequence and print that sequence:</FONT>
<FONT COLOR="#0000ff">print</FONT> cur.<FONT COLOR="#000066">fetchall</FONT>()
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock">
[(<FONT COLOR="#8f8c47">'Putin'</FONT>, <FONT COLOR="#666600">51</FONT>), (<FONT COLOR="#8f8c47">'Yeltsin'</FONT>, <FONT COLOR="#666600">72</FONT>)]
</pre>
<br>
<a name="tutorial_executing_example_2"><h4>Example 2</h4></a>
<p class="textParagraph">
Here's another trivial example that demonstrates various ways of fetching a
single row at a time from a <code>SELECT</code>-cursor:
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(
dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>,
user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>
)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
SELECT <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">"select name_last, age from people order by age, name_last"</FONT>
<FONT COLOR="#32a532"># 1. Iterate over the rows available from the cursor, unpacking the</FONT>
<FONT COLOR="#32a532"># resulting sequences to yield their elements (name_last, age):</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(SELECT)
<FONT COLOR="#0000ff">for</FONT> (name_last, age) <FONT COLOR="#0000ff">in</FONT> cur:
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'%s is %d years old.'</FONT> <FONT COLOR="#7d0000">%</FONT> (name_last, age)
<FONT COLOR="#32a532"># 2. Equivalently:</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(SELECT)
<FONT COLOR="#0000ff">for</FONT> row <FONT COLOR="#0000ff">in</FONT> cur:
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'%s is %d years old.'</FONT> <FONT COLOR="#7d0000">%</FONT> (row[<FONT COLOR="#666600">0</FONT>], row[<FONT COLOR="#666600">1</FONT>])
<FONT COLOR="#32a532"># 3. Using mapping-iteration rather than sequence-iteration:</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(SELECT)
<FONT COLOR="#0000ff">for</FONT> row <FONT COLOR="#0000ff">in</FONT> cur.<FONT COLOR="#000066">itermap</FONT>():
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'%(name_last)s is %(age)d years old.'</FONT> <FONT COLOR="#7d0000">%</FONT> row
<FONT COLOR="#32a532"># 4. Here's the ugly pre-iterator (i.e., Python 2.1) approach:</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(SELECT)
<FONT COLOR="#0000ff">while</FONT> <FONT COLOR="#666600">1</FONT>:
row <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchonemap</FONT>()
<FONT COLOR="#0000ff">if</FONT> <FONT COLOR="#0000ff">not</FONT> row:
<FONT COLOR="#0000ff">break</FONT>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'%(name_last)s is %(age)d years old.'</FONT> <FONT COLOR="#7d0000">%</FONT> row
</pre>
</p>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock">
Putin is 51 years old.
Yeltsin is 72 years old.
Putin is 51 years old.
Yeltsin is 72 years old.
Putin is 51 years old.
Yeltsin is 72 years old.
Putin is 51 years old.
Yeltsin is 72 years old.
</pre>
<br>
<a name="tutorial_executing_example_3"><h4>Example 3</h4></a>
<p class="textParagraph">
The following program is a simplistic table printer
(applied in this example to <code>people</code>):
</p>
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb <FONT COLOR="#0000ff">as</FONT> k
TABLE_NAME <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'people'</FONT>
SELECT <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'select * from %s order by age, name_last'</FONT> <FONT COLOR="#7d0000">%</FONT> TABLE_NAME
con <FONT COLOR="#7d0000">=</FONT> k.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(SELECT)
<FONT COLOR="#32a532"># Print a header.</FONT>
<FONT COLOR="#0000ff">for</FONT> fieldDesc <FONT COLOR="#0000ff">in</FONT> cur.description:
<FONT COLOR="#0000ff">print</FONT> fieldDesc[k.DESCRIPTION_NAME].<FONT COLOR="#000066">ljust</FONT>(fieldDesc[k.DESCRIPTION_DISPLAY_SIZE]) ,
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#32a532"># Finish the header with a newline.</FONT>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'-'</FONT> <FONT COLOR="#7d0000">*</FONT> <FONT COLOR="#666600">78</FONT>
<FONT COLOR="#32a532"># For each row, print the value of each field left-justified within</FONT>
<FONT COLOR="#32a532"># the maximum possible width of that field.</FONT>
fieldIndices <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#4343b8">range</FONT>(<FONT COLOR="#4343b8">len</FONT>(cur.description))
<FONT COLOR="#0000ff">for</FONT> row <FONT COLOR="#0000ff">in</FONT> cur:
<FONT COLOR="#0000ff">for</FONT> fieldIndex <FONT COLOR="#0000ff">in</FONT> fieldIndices:
fieldValue <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#4343b8">str</FONT>(row[fieldIndex])
fieldMaxWidth <FONT COLOR="#7d0000">=</FONT> cur.description[fieldIndex][k.DESCRIPTION_DISPLAY_SIZE]
<FONT COLOR="#0000ff">print</FONT> fieldValue.<FONT COLOR="#000066">ljust</FONT>(fieldMaxWidth) ,
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#32a532"># Finish the row with a newline.</FONT>
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock">
NAME_LAST AGE
------------------------------------------------------------------------------
Putin 51
Yeltsin 72
</pre>
<br>
<a name="tutorial_executing_example_4"><h4>Example 4</h4></a>
<p class="textParagraph">
Let's insert more people into the <code>people</code> table:
</p>
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(
dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>,
user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>
)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
newPeople <FONT COLOR="#7d0000">=</FONT> (
(<FONT COLOR="#8f8c47">'Lebed'</FONT> , <FONT COLOR="#666600">53</FONT>),
(<FONT COLOR="#8f8c47">'Zhirinovsky'</FONT> , <FONT COLOR="#666600">57</FONT>),
)
<FONT COLOR="#0000ff">for</FONT> person <FONT COLOR="#0000ff">in</FONT> newPeople:
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into people (name_last, age) values (?, ?)"</FONT>, person)
<FONT COLOR="#32a532"># The changes will not be saved unless the transaction is committed explicitly:</FONT>
con.<FONT COLOR="#000066">commit</FONT>()
</pre>
<p class="textParagraph">
Note the use of a <em>parameterized</em> SQL statement above. When dealing
with repetitive statements, this is <strong>much faster and less error-prone</strong>
than assembling each SQL statement manually.
</p>
<p class="textParagraph">It's also worth noting that in the example above,
the code:
<pre class="codeBlock" style="margin-left: 15px;"><FONT COLOR="#0000ff">for</FONT> person <FONT COLOR="#0000ff">in</FONT> newPeople:
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into people (name_last, age) values (?, ?)"</FONT>, person)
</pre>
could be rewritten as:
<pre class="codeBlock" style="margin-left: 15px;">cur.<FONT COLOR="#000066">executemany</FONT>(<FONT COLOR="#8f8c47">"insert into people (name_last, age) values (?, ?)"</FONT>, newPeople)
</pre>
</p>
<p class="textParagraph" style="margin-top: 30px;">
After running Example 4, the table printer from Example 3
would print:
</p>
<pre class="programOutputBlock">
NAME_LAST AGE
------------------------------------------------------------------------------
Putin 51
Lebed 53
Zhirinovsky 57
Yeltsin 72
</pre>
<br>
<a name="tutorial_stored_procedures"><h3>Calling Stored Procedures</h3></a>
<p class="textParagraph">
Interbase® and Firebird support stored procedures written in a proprietary
procedural SQL language.
IB/FB stored procedures can have <em>input</em> parameters and/or
<em>output</em> parameters. Some databases support <em>input/output</em>
parameters, where the same parameter is used for both input and output; IB/FB
does not support this.
</p>
<p class="textParagraph">
It is important to distinguish between procedures that <em>return a result set</em>
and procedures that <em>populate and return their output parameters exactly once</em>.
Conceptually, the latter "return their output parameters" like a Python
function, whereas the former "yield result rows" like a Python generator.
</p>
<p class="textParagraph">
IB/FB's <em>server-side</em> procedural SQL syntax
makes no such distinction, but <em>client-side</em> SQL code (and C API code)
must.
A result set is retrieved from a stored procedure by
<code>SELECT</code>ing from the procedure, whereas output
parameters are retrieved with an <code>EXECUTE PROCEDURE</code>
statement.
<br><br>
</p>
<p class="textParagraph">
To <em>retrieve a result set</em> from a stored procedure with KInterbasDB,
use code such as this:
</p>
<pre class="codeBlock">cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select output1, output2 from the_proc(?, ?)"</FONT>, (input1, input2))
<FONT COLOR="#32a532"># Ordinary fetch code here, such as:</FONT>
<FONT COLOR="#0000ff">for</FONT> row <FONT COLOR="#0000ff">in</FONT> cur:
... <FONT COLOR="#32a532"># process row</FONT>
con.<FONT COLOR="#000066">commit</FONT>() <FONT COLOR="#32a532"># If the procedure had any side effects, commit them.</FONT>
</pre>
<p class="textParagraph">
To <em>execute</em> a stored procedure and <em>access its output parameters</em>,
use code such as this:
</p>
<pre class="codeBlock">cur.<FONT COLOR="#000066">callproc</FONT>(<FONT COLOR="#8f8c47">"the_proc"</FONT>, (input1, input2))
<FONT COLOR="#32a532"># If there are output parameters, retrieve them as though they were the</FONT>
<FONT COLOR="#32a532"># first row of a result set. For example:</FONT>
outputParams <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()
con.<FONT COLOR="#000066">commit</FONT>() <FONT COLOR="#32a532"># If the procedure had any side effects, commit them.</FONT>
</pre>
<p class="textParagraph">
This latter is not very elegant; it would be preferable to access the
procedure's output parameters as the return value of
<code>Cursor.callproc</code>. The Python DB API specification requires the
current behavior, however.
</p>
<br><br>
<hr>
<br>
<a name="adv">
<h2 style="margin-bottom: 25px;">Native Database Engine Features and Extensions Beyond the Python DB API</h2>
</a>
<hr>
<a name="adv_db_creation_deletion">
<h2>Programmatic Database Creation and Deletion</h2>
</a>
<p class="textParagraph">
The Firebird engine stores a database in a fairly straightforward manner:
as a single file or, if desired, as a segmented group of files.
</p>
<p class="textParagraph">
The engine supports dynamic database creation via the SQL statement
<code>CREATE DATABASE</code>, which is documented on page 49 of the
<a href="#ref_ib6_docs">Interbase® 6 Language Reference</a>.
</p>
<p class="textParagraph">
The engine also supports dropping (deleting) databases dynamically, but
dropping is a more complicated operation than creating, for several reasons:
an existing database may be in use by users other than the one who requests the
deletion, it may have supporting objects such as temporary sort files, and it may
even have dependent shadow databases. Although the database engine recognizes a
<code>DROP DATABASE</code> SQL statement, support for that statement is
limited to the <code>isql</code> command-line administration utility. However,
the engine supports the deletion of databases via an API call, which
KInterbasDB exposes to Python (see below).
</p>
<p class="textParagraph">
KInterbasDB supports dynamic database creation and deletion via the
module-level function <code>create_database</code> and the method
<code>Connection.drop_database</code>. These are documented below, then
demonstrated by a brief example.
</p>
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">create_database</code>
<span class="memberDocNameCaption">(function; member of <code>kinterbasdb</code>)</span>
</td>
</tr>
<tr>
<td>
<p>
Creates a database according to the supplied <code>CREATE DATABASE</code>
SQL statement. Returns an open connection to the newly created database.
</p>
<p class="argHeader">Arguments:</p>
<ul class="argList">
<li>
<code>sql</code> -
string containing the <code>CREATE DATABASE</code> statement.<br>
<p class="textParagraph">
Note that this statement may need to include a username and password
(see the <a href="#ref_ib6_docs">IB 6 Language Reference</a> for syntax).
</p>
</li>
<li>
<code>dialect</code> <span class="memberDocArgOptTag">(optional)</span> -
the SQL dialect under which to execute the statement
(defaults to <code>3</code>).
</li>
</ul>
</td>
</tr>
</table>
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">drop_database</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.Connection</code>)</span>
</td>
</tr>
<tr>
<td>
<p>
Deletes the database to which the connection is attached.
</p>
<p>
This method performs the database deletion in a responsible
fashion. Specifically, it:
<ul class="argList">
<li>raises an <code>OperationalError</code> instead of deleting
the database if there are other active connections to the
database</li>
<li>deletes supporting files and logs in addition to the
primary database file(s)</li>
</ul>
</p>
<p>
This method has no arguments.
</p>
</td>
</tr>
</table>
<p class="textParagraph" style="margin-top: 1.5em;">
Example program:
</p>
<pre class="codeBlock" style="margin-top: 0px;"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">create_database</FONT>(
<FONT COLOR="#8f8c47">"create database '/temp/db.db' user 'sysdba' password 'pass'"</FONT>
)
con.<FONT COLOR="#000066">drop_database</FONT>()</pre>
<hr>
<a name="adv_event"><h2>Database Event Notification</h2></a>
<ul style="margin-bottom: 2em;">
<li><a href="#adv_event_what">What are database events?</a></li>
<li><a href="#adv_event_why">Why use database events?</a></li>
<li><a href="#adv_event_native_exposure">
How does the database engine expose events to SQL (in the server process)
and C (in the client process)?
</a>
</li>
<li><a href="#adv_event_python_exposure">
How does KInterbasDB expose database events to the Python programmer?
</a>
</li>
<li><a href="#adv_event_example">Example Program</a></li>
<li><a href="#adv_event_limitations">Pitfalls and Limitations</a></li>
</ul>
<a name="adv_event_what"><h4>What are database events?</h4></a>
<p class="textParagraph">
The database engine features a distributed, interprocess communication
mechanism based on messages called <em>database events</em>.
Chapter 11 of the
<a href="#ref_ib6_docs">Interbase® 6 API Guide</a>
describes database events this way:
</p>
<blockquote>
[A database event is] a message passed from a trigger or stored procedure to an
application to
announce the occurrence of a specified condition or action, usually a database
change such as an insertion, modification, or deletion of a record.
</blockquote>
<blockquote>
The Interbase® [and Firebird] event mechanism enables applications to respond
to actions and database changes made by other, concurrently running
applications without the need for those applications to communicate directly
with one another, and without incurring the expense of CPU time required for
periodic polling to determine if an event has occurred.
</blockquote>
<a name="adv_event_why"><h4>Why use database events?</h4></a>
<p class="textParagraph">
Anything that can be accomplished with database events can also be
implemented using other techniques, so why bother with events?
Since you've chosen to write database-centric programs in Python rather
than assembly language, you probably already know the answer to this
question, but let's illustrate.
</p>
<p class="textParagraph">
A classic application for database events is the handling of administrative
messages. Suppose you have an administrative message database with a
<code>messages</code> table, into which various applications insert timestamped
status reports. It may be desirable to react to these messages in diverse ways,
depending on the status they indicate:
to ignore them,
to initiate the update of dependent databases upon their arrival,
to forward them by e-mail to a remote administrator,
or even to set off an audible alarm so that on-site administrators will know
a problem has occurred.
</p>
<p class="textParagraph">
It is undesirable to tightly couple the program whose status is being reported
(the <em>message producer</em>) to the program that handles the status reports
(the <em>message handler</em>).
There are obvious losses of flexibility in doing so.
For example, the message producer may run on a separate machine from the
administrative message database and may lack access rights to the downstream
reporting facilities (e.g., network access to the SMTP server, in the case of
forwarded e-mail notifications). Additionally, the actions required to
handle status reports may themselves be time-consuming and
error-prone, as in accessing a remote network to transmit e-mail.
</p>
<p class="textParagraph">
In the absence of database event support, the message handler would probably
be implemented via <em>polling</em>. Polling is simply the repetition of
a check for a condition at a specified interval.
In this case, the message handler would check in an infinite loop to see
whether the most recent record in the <code>messages</code> table was more
recent than the last message it had handled. If so, it would handle the
fresh message(s); if not, it would go to sleep for a specified interval,
then loop.
</p>
<p class="textParagraph">
The <em>polling-based</em> implementation of the message handler is
fundamentally flawed. Polling is a form of
<a href="http://www.catb.org/~esr/jargon/html/entry/busy-wait.html">busy-wait</a>;
the check for new messages is performed at the specified interval, regardless
of the actual activity level of the message producers.
If the polling interval is lengthy,
messages might not be handled within a reasonable time period after their arrival;
if the polling interval is brief, the message handler program (and there may
be many such programs) will waste a large amount of CPU time on unnecessary
checks.
</p>
<p class="textParagraph">
The database server is necessarily aware of the exact moment
when a new message arrives. Why not let the message handler program request
that the database server send it a notification when a new message arrives?
The message handler can then efficiently sleep until the moment its services
are needed. Under this <em>event-based</em>
scheme, the message handler becomes aware of new messages at the instant
they arrive, yet it does not waste CPU time checking in vain for new messages
when none is available.
</p>
<a name="adv_event_native_exposure">
<h4>How does the database engine expose events to SQL (in the server process)
and C (in the client process)?
</h4>
</a>
<p class="textParagraph">
<ol>
<li style="margin-bottom: 1.5em;">Server Process
<span style="font-size: 85%;">("An event just occurred!")</span>
<p class="textParagraph">
Recall from Chapter 11 of the
<a href="#ref_ib6_docs">Interbase® 6 API Guide</a>
that
</p>
<blockquote style="margin-top: 0px;">
[A database event is] a message passed from a trigger or stored procedure
to an application to announce the occurrence of a specified condition or
action, usually a database change such as an insertion, modification, or
deletion of a record.
</blockquote>
<p class="textParagraph">
To notify any interested listeners that a specific event has occurred,
issue the
<code>POST_EVENT</code> statement
(see page 176 of the <a href="#ref_ib6_docs">Interbase® 6 Language Reference</a>).
The <code>POST_EVENT</code> statement has one parameter: the name of the
event to post.
</p>
<p class="textParagraph">
In the preceding example of the administrative message database,
<code>POST_EVENT</code> might be used from an <code>after insert</code>
trigger on the <code>messages</code> table, like this:
</p>
<pre class="codeBlock" style="margin-top: 0px;">create trigger trig_messages_handle_insert
for messages
after insert
as
begin
<span style="color: blue;">POST_EVENT</span> 'new_message';
end
</pre>
<p class="textParagraph">
Note that the physical notification of the client process does not occur until the
transaction in which the <code>POST_EVENT</code> took place is actually
committed. Therefore, multiple events may <em>conceptually</em> occur
before the client process is <em>physically</em> informed of even one
occurrence.
</p>
<p class="textParagraph">Furthermore, the database engine makes no
guarantee that clients will be informed of events in the same groupings
in which they conceptually occurred. If, within a single transaction, an event
named <code>event_a</code> is posted once and an event named
<code>event_b</code> is posted once, the client may receive those posts
in separate "batches", despite the fact that they occurred in the same
conceptual unit (a single transaction). This also applies to multiple
occurrences of <em>the same</em> event within a single conceptual unit: the
physical notifications may arrive at the client separately.
</p>
</li>
<li>Client Process <span style="font-size: 85%;">("Send me a message when an event occurs.")</span><br>
<p class="textParagraph" style="margin-bottom: 1.5em;">
<strong>Note:</strong>
This section is intended mainly as an implementation hint to the authors of
future libraries based on the Firebird C client library, and as a reminder
to the author David Rushby himself, stored away in plain sight as a
vaccination against the recurrence of the headaches that ensued from his
attempt to use the most abysmally documented area of the Firebird C API.
If you're a Python programmer who doesn't care about the gory details
and isn't anxious to read a whole series of sentences as long as the
previous one, skip to the section that describes
<a href="#adv_event_python_exposure">KInterbasDB's Python-level event handling API</a>.
</p>
<p class="textParagraph">
The Interbase®/Firebird C client library offers two forms of event notification.
</p>
<p class="textParagraph">
The first form is <em>synchronous</em> notification, by way of the function
<code>isc_wait_for_event</code>. This form is admirably simple for a C
programmer to use, but completely inappropriate as a basis for KInterbasDB's
event support, for two reasons.
The database's C client library implements <code>isc_wait_for_event</code>
via <em>process suspension</em>, which puts the entire process to sleep until
an event notification arrives. This behavior clashes with
multithreaded programs, which may need to have one thread enter
a blocking wait for event notifications while other threads remain active.
Secondly, process suspension is not available on the Windows platform, and the
database client library does not implement <code>isc_wait_for_event</code>
on Linux.
Although the implementation of <code>isc_wait_for_event</code> makes it
unsuitable for use by the internals of KInterbasDB, the ease with which
it exposes database event notification to the client programmer is quite
Pythonic, a fact that was
<a href="#adv_event_python_exposure">not lost</a> on the bleary-eyed
Mr. Rushby.
</p>
<p class="textParagraph">
The other form of event notification offered by the database client library
is <em>asynchronous</em>, by way of the functions
<code>isc_que_events</code> (apparently the letters
<code>u</code> and <code>e</code> were in short supply that day),
<code>isc_cancel_events</code>, and others.
</p>
<p class="textParagraph">
The details are as nasty as they are numerous, but the essence of using
asynchronous notification from C is as follows:
</p>
<ol style="margin-left: 3em;">
<li>Call <code>isc_event_block</code> to create a formatted binary buffer
that will tell the server which events the client wants to listen for.
</li>
<li>Call <code>isc_que_events</code> (passing the buffer created in the
previous step) to inform the server that the client is ready to receive
event notifications, and provide a callback that will be asynchronously
invoked when one or more of the registered events occurs.
</li>
<li>[The thread that called <code>isc_que_events</code> to initiate event
listening must now do something else.]
</li>
<li>When the callback is invoked (the database client library starts a thread
dedicated to this purpose), it can use the <code>isc_event_counts</code>
function to determine how many times each of the registered events has
occurred since the last call to <code>isc_event_counts</code> (if any).
</li>
<li>[The callback thread should now "do its thing", which may include
communicating with the thread that called <code>isc_que_events</code>.]
</li>
<li>When the callback thread is finished handling an event notification, it
must call <code>isc_que_events</code> again in order to receive future
notifications. Future notifications will invoke the callback again,
effectively "looping" the callback thread back to Step 4.
</li>
</ol>
<p class="textParagraph">
As implemented by the Interbase®/Firebird C client library, asynchronous event
notification suffers from a significant limitation: only one thread per
process can listen for events at any given time.
</p>
<p class="textParagraph">
The rest of this section describes the C-level internals of KInterbasDB's event
support; the exposed Python API is documented in
<a href="#adv_event_python_exposure">the next section</a>.
</p>
<p class="textParagraph">
KInterbasDB's event-related internals conform loosely to the outline
above, although the Python interpreter's own threading limitations complicate
matters greatly.
Let's fill in the blanks of Steps 3 and 5 from the outline with
specific descriptions.
</p>
<p class="textParagraph" style="font-style: italic;">
3. [The thread that called <code>isc_que_events</code> to initiate event
listening must now do something else.]
</p>
<p class="textParagraph">
In KInterbasDB, "<i>the thread that called <code>isc_que_events</code> to
initiate event listening</i>" is a native thread started by Python
(either explicitly by the Python programmer, or implicitly by the Python
interpreter to run the main program); let's call it Thread-Py.
</p>
<p class="textParagraph">
Thread-Py, running in KInterbasDB's C layer, executes Steps 1 and 2, then
<em>waits</em> on a native event object (on Win32, an <code>Event</code>;
on POSIX, a pair of <code>pthread_cond_t</code> and <code>pthread_mutex_t</code>).
</p>
<p class="textParagraph" style="font-style: italic;">
5. [The callback thread should now "do its thing", which may include
communicating with the thread that called <code>isc_que_events</code>.]
</p>
<p class="textParagraph">
In KInterbasDB, the "<i>callback thread</i>" is a native thread started by the
database's C client library; let's call it Thread-Ev.
</p>
<p class="textParagraph">
The client library actually starts Thread-Ev as soon as Thread-Py calls
<code>isc_que_events</code>, without waiting for any events to occur. This
initial "dummy run" gives Thread-Ev a chance to perform any necessary
initialization. In KInterbasDB, this consists merely of clearing the buffer
used to tally the occurrence counts of the registered events (and of
re-queueing Thread-Ev to receive future event notifications--Step 6 from
the outline).
</p>
<p class="textParagraph">
Thread-Ev, having been started by the database client library rather than
the Python interpreter, is a "naked" native thread. Although any thread
started via Python's <code>thread</code> or <code>threading</code> modules
is a full-fledged native thread, a "naked" thread must have Python
threadstate bootstrapped onto it before the Python interpreter can execute
Python code on that thread.
Thread-Ev does not need any Python threadstate, however, because KInterbasDB's
C-level event callback function is designed to avoid Python code and operate
solely in native C.
</p>
<p class="textParagraph">
Step 5 consists of the callback thread
"<span style="font-style: italic;">doing its thing</span>"; in KInterbasDB,
the mission of Thread-Ev during a given iteration of the event callback is
threefold:
first, to supply Thread-Py with enough information to generate
the return value required by the interface of the
<code>EventConduit.wait</code> method;
secondly, to notify Thread-Py that an event has occurred;
and finally (Step 6 from the outline) for Thread-Ev to re-queue itself
via <code>isc_que_events</code> so that the callback will be invoked upon
the occurrence of future events.
</p>
<p class="textParagraph">
To accomplish the first element of the mission, Thread-Ev inserts a node
into a C linked list associated with the <code>EventConduit</code> upon
which Thread-Py is <code>wait</code>ing.
Every <code>EventConduit</code> holds a C linked list of type
<code>EventQueue</code>. An <code>EventQueue</code> is comprised of
<code>EventQueueItem</code>s; each <code>EventQueueItem</code> contains an
array of C <code>long</code>s. This array is designed to hold the occurrence
counts of the registered events, as reported by <code>isc_event_counts</code>
during the ongoing iteration of the event callback by Thread-Ev.
</p>
<p class="textParagraph">
Secondly, Thread-Ev issues a native event notification
(<code>SetEvent</code> on Win32; <code>pthread_cond_signal</code> on POSIX)
to release Thread-Py from its blocking call to <code>EventConduit.wait</code>.
</p>
<p class="textParagraph">
Finally, Thread-Ev re-queues itself via <code>isc_que_events</code>, and
control of the thread passes out of the callback and back into the database
client library.
The database client library does not start and destroy a new thread per
event notification; rather, it starts the thread we've nicknamed Thread-Ev
upon the first call to <code>isc_que_events</code>, then
reuses that same thread for all future event notifications within the same
process. This thread is recycled even for notifications that concern a
different set of event names (in KInterbasDB terminology, "even for a different
<code>EventConduit</code> object").
</p>
<p class="textParagraph">
When Thread-Py is awakened by Thread-Ev, it retrieves the head
<code>EventQueueItem</code> from the <code>EventQueue</code>, extracts the
<code>long</code> values from that node's <code>count</code> array into a
Python dictionary that maps
<code>event name -> event occurrence count</code>,
and returns the dictionary to the Python programmer as the return value of
<code>EventConduit.wait</code>.
</p>
<p class="textParagraph">
Throughout this process, responsible thread synchronization is observed
(with respect to the Python interpreter, the database client library, and
a specific <code>EventQueue</code>).
There is one avoidable scenario in which deadlocks are possible; it is
documented in the
<a href="#adv_event_limitations">Pitfalls and Limitations</a> subsection.
</p>
<p class="textParagraph">
The high-level event handling API that KInterbasDB exposes to the Python
programmer is documented in the next section.
</p>
</li>
</ol>
<a name="adv_event_python_exposure">
<h4>How does KInterbasDB expose database events to the Python programmer?</h4>
</a>
<p class="textParagraph">
The KInterbasDB database event API is comprised of the following:
the method <code>Connection.event_conduit</code> and the class
<code>EventConduit</code>.
</p>
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">event_conduit</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.Connection</code>)</span>
</td>
</tr>
<tr>
<td>
<p>
Creates a conduit (an instance of <code>EventConduit</code>) through
which database event notifications will flow into the Python program.
</p>
<p>
<code>event_conduit</code> is a method of <code>Connection</code>
rather than a module-level function or a class constructor because
the database engine deals with events in the context of a particular
database (after all, <code>POST_EVENT</code> must be issued by a
stored procedure or a trigger).
</p>
<p class="argHeader">Arguments:</p>
<ul class="argList">
<li>
<code>event_names</code> -
a sequence of string event names<br>
<p class="textParagraph">
The <code>EventConduit.wait</code> method will block until the
occurrence of at least one of the events named by the strings in
<code>event_names</code>.
</p>
</li>
</ul>
</td>
</tr>
</table>
<p class="compactParagraph" style="font-size: 100%;">
<code>EventConduit:</code>
</p>
<!-- kinterbasdb.EventConduit.__init__ -->
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">__init__</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.EventConduit</code>)</span>
</td>
</tr>
<tr>
<td>
<p>
The <code>EventConduit</code> class is not designed to be instantiated
directly by the Python programmer. Instead, use the
<code>Connection.event_conduit</code> method to create
<code>EventConduit</code> instances.
</p>
</td>
</tr>
</table>
<!-- kinterbasdb.EventConduit.wait -->
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">wait</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.EventConduit</code>)</span>
</td>
</tr>
<tr>
<td>
<p class="compactParagraph">
Blocks the calling thread until at least one of the events occurs,
or the specified <code>timeout</code> (if any) expires.
</p>
<p class="compactParagraph">
If one or more event notifications has arrived since the last call
to <code>wait</code>, this method will retrieve a notification from
the head of the <code>EventConduit</code>'s internal queue and
return immediately.
</p>
<p class="compactParagraph" style="margin-bottom: 0px;">
The names of the relevant events were supplied to the
<code>Connection.event_conduit</code> method during the creation
of this <code>EventConduit</code>.
In the code snippet below, the relevant events are named
<code>event_a</code> and <code>event_b</code>:
</p>
<pre class="codeBlockInMemberDoc">conduit <FONT COLOR="#7d0000">=</FONT> connection.<FONT COLOR="#000066">event_conduit</FONT>( (<FONT COLOR="#8f8c47">'event_a'</FONT>, <FONT COLOR="#8f8c47">'event_b'</FONT>) )
conduit.<FONT COLOR="#000066">wait</FONT>()
</pre>
<p class="argHeader">Arguments:</p>
<ul class="argList">
<li><code>timeout</code> <em>(optional)</em> -
number of seconds (use a <code>float</code> to indicate fractions of seconds)<br>
<p class="textParagraph">
If not even one of the relevant events has occurred after
<code>timeout</code> seconds, this method will unblock and return
<code>None</code>.
The default <code>timeout</code> is infinite.
</p>
</li>
</ul>
<p class="retHeader">Returns:</p>
<p class="retDesc">
<code>None</code> if the wait timed out, otherwise a dictionary
that maps <code>event_name -> event_occurrence_count</code>.
</p>
<p class="compactParagraph" style="margin-bottom: 0px;">
In the code snippet above, if <code>event_a</code> occurred once and
<code>event_b</code> did not occur at all, the return value from
<code>conduit.wait()</code> would be the following dictionary:
</p>
<pre class="codeBlockInMemberDoc">{
<FONT COLOR="#8f8c47">'event_a'</FONT>: <FONT COLOR="#666600">1</FONT>,
<FONT COLOR="#8f8c47">'event_b'</FONT>: <FONT COLOR="#666600">0</FONT>
}
</pre>
</td>
</tr>
</table>
<!-- kinterbasdb.EventConduit.close -->
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">close</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.EventConduit</code>)</span>
</td>
</tr>
<tr>
<td>
<p class="compactParagraph">
Cancels the standing request for this conduit to be notified of events,
clearing the way for the creation of another
<code>EventConduit</code>
(via the <code>Connection.event_conduit</code> method).
</p>
<p class="compactParagraph">
After this method has been called, this <code>EventConduit</code>
object is useless, and should be discarded.
</p>
<p class="compactParagraph">
This method has no arguments.
</p>
</td>
</tr>
</table>
<!-- kinterbasdb.EventConduit.flush -->
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">flush</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.EventConduit</code>)</span>
</td>
</tr>
<tr>
<td>
<p class="compactParagraph">
This method allows the Python programmer to manually clear any
event notifications that have queued up since the last
<code>wait</code> call.
</p>
<p class="compactParagraph">
After the first <code>wait</code> call on a given
<code>EventConduit</code>, notifications of any events that occur
will accumulate asynchronously within the conduit's internal
queue until the conduit is <code>close</code>d either explicitly or
implicitly (via garbage collection). There are two ways to dispose
of the accumulated notifications: call <code>wait</code> to receive
them one at a time (<code>wait</code> will block when the conduit's
internal queue is empty), or call this method to get rid of all
accumulated notifications.
</p>
<p class="compactParagraph">
This method has no arguments.
</p>
<p class="retHeader">Returns:</p>
<p class="retDesc">
The number of event notifications that were flushed from the queue.
The "number of event <em>notifications</em>" is not necessarily the
same as the "number of event <em>occurrences</em>", since a single
notification can indicate multiple occurrences of a given event
(see the return value of the <code>wait</code> method).
</p>
</td>
</tr>
</table>
<br><br>
<a name="adv_event_example"><h4>Example Program</h4></a>
<p class="textParagraph">
The following code (a SQL table definition, a SQL trigger definition, and
two Python programs) demonstrates KInterbasDB-based event notification.
</p>
<p class="textParagraph">
The example is based on a database at
<code>'localhost:/temp/test.db'</code>, which contains
a simple table named <code>test_table</code>.
<code>test_table</code> has an <code>after insert</code>
trigger that posts several events.
Note that the trigger posts <code>test_event_a</code> twice,
<code>test_event_b</code> once, and <code>test_event_c</code> once.
</p>
<p class="textParagraph">
The Python event <em>handler</em> program connects to the database and
establishes an <code>EventConduit</code> in the context of that connection.
As specified by the list of <code>RELEVANT_EVENTS</code> passed to
<code>event_conduit</code>, the event conduit
will concern itself only with events named <code>test_event_a</code>
and <code>test_event_b</code>.
Next, the program calls the conduit's <code>wait</code> method
without a timeout; it will wait infinitely until <em>at least one</em>
of the relevant events is posted in a transaction that is
subsequently committed.
</p>
<p class="textParagraph">
The Python event <em>producer</em> program simply connects to the database,
inserts a row into <code>test_table</code>, and commits the transaction.
Notice that except for the printed comment, no code in the producer
makes any mention of events--the events are posted as an implicit
consequence of the row's insertion into <code>test_table</code>.
</p>
<p class="textParagraph">
The insertion into <code>test_table</code> causes the trigger
to <em>conceptually</em> post events, but those events are not
<em>physically</em> sent to interested listeners until the transaction
is committed.
When the commit occurs, the handler program returns from the <code>wait</code>
call and prints the notification that it received.
</p>
<p style="margin-bottom: 0px;">
SQL table definition:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
create table test_table (a integer)
</pre>
<p style="margin-bottom: 0px;">
SQL trigger definition:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
create trigger trig_test_insert_event
for test_table
after insert
as
begin
POST_EVENT 'test_event_a';
POST_EVENT 'test_event_b';
POST_EVENT 'test_event_c';
POST_EVENT 'test_event_a';
end
</pre>
<p style="margin-bottom: 0px;">
Python event <em>handler</em> program:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
RELEVANT_EVENTS <FONT COLOR="#7d0000">=</FONT> [<FONT COLOR="#8f8c47">'test_event_a'</FONT>, <FONT COLOR="#8f8c47">'test_event_b'</FONT>]
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
conduit <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">event_conduit</FONT>(RELEVANT_EVENTS)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'HANDLER: About to wait for the occurrence of one of %s...\n'</FONT> <FONT COLOR="#7d0000">%</FONT> RELEVANT_EVENTS
result <FONT COLOR="#7d0000">=</FONT> conduit.<FONT COLOR="#000066">wait</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'HANDLER: An event notification has arrived:'</FONT>
<FONT COLOR="#0000ff">print</FONT> result
conduit.<FONT COLOR="#000066">close</FONT>()
</pre>
<p style="margin-bottom: 0px;">
Python event <em>producer</em> program:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test_table values (1)"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'PRODUCER: Committing transaction that will cause event notification to be sent.'</FONT>
con.<FONT COLOR="#000066">commit</FONT>()
</pre>
<p style="margin-bottom: 0px;">
Event producer output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
PRODUCER: Committing transaction that will cause event notification to be sent.
</pre>
<p style="margin-bottom: 0px;">
Event handler output (assuming that the handler was already started and waiting
when the event producer program was executed):
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
HANDLER: About to wait for the occurrence of one of ['test_event_a', 'test_event_b']...
HANDLER: An event notification has arrived:
{'test_event_a': 2, 'test_event_b': 1}
</pre>
<p class="textParagraph">
Notice that there is no mention of <code>test_event_c</code> in the result
dictionary received by the event handler program.
Although <code>test_event_c</code> was posted by the <code>after insert</code>
trigger, the event conduit in the handler program was created to
listen only for <code>test_event_a</code> and
<code>test_event_b</code> events.
</p>
<br>
<a name="adv_event_limitations">
<h4>Pitfalls and Limitations</h4>
</a>
<ul>
<li>
<p>
Only one <code>EventConduit</code> can be active in a single process
at any given time
(limitation imposed by the database client library).<br>
KInterbasDB enforces this limitation by raising an exception if the Python programmer tries to breach it.
</p>
</li>
<li>
<p>
No more than 16 event names can be <code>wait</code>ed for with
a single <code>EventConduit</code>
(limitation imposed by the database client library).<br>
KInterbasDB enforces this limitation by raising an exception if the Python programmer tries to breach it.
</p>
</li>
<li>
<p>
Remember that if an <code>EventConduit</code> is left active (not yet
<code>close</code>d or garbage collected), notifications for any
registered events that actually occur
will continue to accumulate in the <code>EventConduit</code>'s
internal queue even if the Python programmer doesn't call
<code>EventConduit.wait</code> to receive the notifications or
<code>EventConduit.flush</code> to clear the queue.
The ill-informed may misinterpret this behavior as a memory leak in
KInterbasDB; it is not.
</p>
</li>
<li>
<span style="color: red; font-weight: bold;">
NEVER use LOCAL-protocol connections in a multithreaded program that
also uses event handling!
</span><br>
<p class="textParagraph">
The database client library implements the local protocol on some
platforms in such a way that deadlocks may arise in bizarre places if
you do this.
<em>This no-LOCAL prohibition is not limited to connections that are
used as the basis for event conduits; it applies to all connections
throughout the process.</em>
</p>
<p class="textParagraph">
So why doesn't KInterbasDB protect the Python programmer from this
mistake? Because the event handling thread is started by the
database client library, and it
<a href="#adv_event_native_exposure">operates</a>
beyond the synchronization domain of KInterbasDB at times.
</p>
</li>
</ul>
<br>
<hr>
<br>
<a name="adv_trans_control">
<h2>Advanced Transaction Control</h2>
</a>
<p class="textParagraph">
For the sake of simplicity, KInterbasDB lets the Python programmer
ignore transaction management to the greatest extent allowed by the
Python Database API Specification 2.0. The specification says,
"if the database supports an auto-commit feature, this must be
initially off". At a minimum, therefore, it is necessary to call the
<code>commit</code> method of the connection in order to persist any
changes made to the database. Transactions left unresolved by the
programmer will be <code>rollback</code>ed when the connection is
garbage collected.
</p>
<p class="textParagraph">
Remember that because of
<a href="http://philip.greenspun.com/panda/databases-choosing#acid">ACID</a>,
every data manipulation operation in the Interbase®/Firebird database engine
takes place in the context of a transaction, including operations that are
conceptually "read-only", such as a typical <code>SELECT</code>.
The client programmer of KInterbasDB establishes a transaction
implicitly by using any SQL execution method, such as
<code>Connection.execute_immediate</code>, <code>Cursor.execute</code>,
or <code>Cursor.callproc</code>.
</p>
<p class="textParagraph">
Although KInterbasDB allows the programmer to pay little attention to
transactions, it also exposes the full complement of the database engine's
advanced transaction control features:
transaction parameters, retaining transactions, savepoints, and
distributed transactions.
</p>
<br>
<a name="adv_trans_control_parameters"><h4>Transaction Parameters</h4></a>
<p class="textParagraph">
The database engine offers the client programmer an optional facility called
<em>transaction parameter buffers</em> (TPBs) for tweaking the operating characteristics
of the transactions he initiates. These include characteristics such as
"whether the transaction has read and write access to tables,
or read-only access, and whether or not other simultaneously active
transactions can share table access with the transaction"
(<a href="#ref_ib6_docs">IB 6 API Guide</a>, page 62).
</p>
<p class="textParagraph">
In addition to the implicit transaction initiation mentioned in the
<a href="#adv_trans_control">introduction</a> of this section, KInterbasDB
allows the programmer to start transactions explicitly via the
<code>Connection.begin</code> method.
Connections have a <code>default_tpb</code> attribute
that can be changed to set the default TPB for all transactions subsequently
started on the connection.
Alternatively, if the programmer only wants to set the TPB for a single
transaction, he can start a transaction explicitly via the
<code>Connection.begin</code> method and pass a TPB for that single
transaction.
</p>
<p class="textParagraph">
For details about TPB construction, see Chapter 5 of the
<a href="#ref_ib6_docs">Interbase® 6 API Guide</a>.
In particular, page 63 of that document presents a table of possible
TPB elements--single bytes that the C API defines as constants whose names
begin with <code>isc_tpb_</code>.
KInterbasDB makes all of those TPB constants available (under the same names)
as module-level constants in the form of single-character strings.
A transaction parameter <em>buffer</em> is handled in C as a
character array; KInterbasDB requires that TPBs be constructed as Python
strings. Since the constants in the <code>kinterbasdb.isc_tpb_*</code>
family are single-character Python strings, they can simply be concatenated
to create a TPB.
<br><br>
</p>
<p class="textParagraph">
The following example program uses explicit transaction initiation and TPB
construction to establish an unobtrusive transaction for read-only
access to the database:
</p>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
<FONT COLOR="#32a532"># Construct a TPB by concatenating single-character strings (bytes)</FONT>
<FONT COLOR="#32a532"># from the kinterbasdb.isc_tpb_* family.</FONT>
customTPB <FONT COLOR="#7d0000">=</FONT> (
kinterbasdb.isc_tpb_read
<FONT COLOR="#7d0000">+</FONT> kinterbasdb.isc_tpb_read_committed
<FONT COLOR="#7d0000">+</FONT> kinterbasdb.isc_tpb_rec_version
)
<FONT COLOR="#32a532"># Explicitly start a transaction with the custom TPB:</FONT>
con.<FONT COLOR="#000066">begin</FONT>(tpb<FONT COLOR="#7d0000">=</FONT>customTPB)
<FONT COLOR="#32a532"># Now read some data using cursors:</FONT>
...
<FONT COLOR="#32a532"># Commit the transaction with the custom TPB. Future transactions</FONT>
<FONT COLOR="#32a532"># opened on con will not use a custom TPB unless it is explicitly</FONT>
<FONT COLOR="#32a532"># passed to con.begin every time, as it was above, or</FONT>
<FONT COLOR="#32a532"># con.default_tpb is changed to the custom TPB, as in:</FONT>
<FONT COLOR="#32a532"># con.default_tpb = customTPB</FONT>
con.<FONT COLOR="#000066">commit</FONT>()
</pre>
<br>
<a name="adv_trans_control_retaining"><h4>Retaining Operations</h4></a>
<p class="textParagraph">
The <code>commit</code> and <code>rollback</code> methods of
<code>kinterbasdb.Connection</code>
accept an optional boolean parameter <code>retaining</code>
(default <code>False</code>) to indicate whether to recycle the
transactional context of the transaction being resolved by the
method call.
</p>
<p class="textParagraph">
If <code>retaining</code> is <code>True</code>, the infrastructural
support for the transaction active
at the time of the method call will be "retained" (efficiently and
transparently recycled) after the database server has committed or rolled
back the conceptual transaction.
In code that commits or rolls back frequently, "retaining" the
transaction yields considerably better performance.
</p>
<p class="textParagraph">
For more information about retaining transactions, see page 291 of the
<a href="#ref_ib6_docs">Interbase® 6 API Guide</a>.
</p>
<br>
<a name="adv_trans_control_savepoints"><h4>Savepoints</h4></a>
<p class="textParagraph">
Firebird 1.5 introduced support for transaction savepoints.
Savepoints are named, intermediate control points within an open transaction
that can later be rolled back to, without affecting the preceding work.
Multiple savepoints can exist within a single unresolved transaction,
providing "multi-level undo" functionality.
</p>
<p class="textParagraph">
Although Firebird savepoints are fully supported from SQL alone via the
<code>SAVEPOINT 'name'</code> and <code>ROLLBACK TO 'name'</code>
statements, KInterbasDB also exposes savepoints at the Python API level
for the sake of convenience.
The method <code>Connection.savepoint(name)</code> establishes a savepoint
with the specified <code>name</code>.
To roll back to a specific savepoint, call the
<code>Connection.rollback</code> method and provide a value (the name of
the savepoint) for the optional <code>savepoint</code> parameter.
If the <code>savepoint</code> parameter of <code>Connection.rollback</code>
is not specified, the active transaction is cancelled in its entirety,
as required by the Python Database API Specification.
</p>
<p class="textParagraph">
The following example program demonstrates savepoint manipulation via
the KInterbasDB API, rather than raw SQL.
</p>
<span style="color: blue;"></span>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"recreate table test_savepoints (a integer)"</FONT>)
con.<FONT COLOR="#000066">commit</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'Before the first savepoint, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test_savepoints values (?)"</FONT>, [<FONT COLOR="#666600">1</FONT>])
<strong>con.<FONT COLOR="#000066">savepoint</FONT>(<FONT COLOR="#8f8c47">'A'</FONT>)</strong>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'After savepoint A, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test_savepoints values (?)"</FONT>, [<FONT COLOR="#666600">2</FONT>])
<strong>con.<FONT COLOR="#000066">savepoint</FONT>(<FONT COLOR="#8f8c47">'B'</FONT>)</strong>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'After savepoint B, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test_savepoints values (?)"</FONT>, [<FONT COLOR="#666600">3</FONT>])
<strong>con.<FONT COLOR="#000066">savepoint</FONT>(<FONT COLOR="#8f8c47">'C'</FONT>)</strong>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'After savepoint C, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
<strong>con.<FONT COLOR="#000066">rollback</FONT>(savepoint<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'A'</FONT>)</strong>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'After rolling back to savepoint A, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
<strong>con.<FONT COLOR="#000066">rollback</FONT>()</strong>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'After rolling back entirely, the contents of the table are:'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_savepoints"</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">' '</FONT>, cur.<FONT COLOR="#000066">fetchall</FONT>()
</pre>
<p class="textParagraph">
The output of the example program is shown below.
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
Before the first savepoint, the contents of the table are:
[]
After savepoint A, the contents of the table are:
[(1,)]
After savepoint B, the contents of the table are:
[(1,), (2,)]
After savepoint C, the contents of the table are:
[(1,), (2,), (3,)]
After rolling back to savepoint A, the contents of the table are:
[(1,)]
After rolling back entirely, the contents of the table are:
[]
</pre>
<br>
<a name="adv_trans_control_distributed"><h4>Distributed Transactions</h4></a>
<span class="XXX_ADDRESS_THIS">XXX: KInterbasDB's support for distributed
transactions has not yet been thoroughly documented. In the meantime, read the
source code for the <code>kinterbasdb.ConnectionGroup</code> class
and examine the brief example program below.</span>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
<FONT COLOR="#32a532"># Establish multiple connections the usual way:</FONT>
con1 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'stalin:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
con2 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'bison:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
<FONT COLOR="#32a532"># Create a ConnectionGroup to associate multiple connections in such a</FONT>
<FONT COLOR="#32a532"># way that they can participate in a distributed transaction.</FONT>
<FONT COLOR="#32a532"># !!!</FONT>
<FONT COLOR="#32a532"># NO TWO MEMBERS OF A SINGLE CONNECTIONGROUP SHOULD BE ATTACHED TO THE SAME DATABASE!</FONT>
<FONT COLOR="#32a532"># !!!</FONT>
group <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">ConnectionGroup</FONT>( connections<FONT COLOR="#7d0000">=</FONT>(con1,con2) )
<FONT COLOR="#32a532"># Start a distributed transaction involving all of the members of the group</FONT>
<FONT COLOR="#32a532"># (con1 and con2 in this case) with one of the following approaches:</FONT>
<FONT COLOR="#32a532"># - Call group.begin()</FONT>
<FONT COLOR="#32a532"># - Call con1.begin(); the operation will "bubble upward" and apply to the group.</FONT>
<FONT COLOR="#32a532"># - Call con2.begin(); the operation will "bubble upward" and apply to the group.</FONT>
<FONT COLOR="#32a532"># - Just start executing some SQL statements on either con1 or con2.</FONT>
<FONT COLOR="#32a532"># A transaction will be started implicitly; it will be a distributed</FONT>
<FONT COLOR="#32a532"># transaction because con1 and con2 are members of a ConnectionGroup.</FONT>
group.<FONT COLOR="#000066">begin</FONT>()
<FONT COLOR="#32a532"># Perform some database changes the usual way (via cursors on con1 and con2):</FONT>
...
<FONT COLOR="#32a532"># Commit or roll back the distributed transaction by calling the commit</FONT>
<FONT COLOR="#32a532"># or rollback method of the ConnectionGroup itself, or the commit or</FONT>
<FONT COLOR="#32a532"># rollback method of any member connection (con1 or con2 in this case).</FONT>
group.<FONT COLOR="#000066">commit</FONT>()
<FONT COLOR="#32a532"># Unless you want to perform another distributed transaction, disband the</FONT>
<FONT COLOR="#32a532"># group so that member connections can operate independently again.</FONT>
group.<FONT COLOR="#000066">clear</FONT>()
</pre>
<p style="margin-bottom: 0px;"><strong>Notes:</strong></p>
<p class="textParagraph">
While a <code>Connection</code> belongs to a
<code>ConnectionGroup</code>, any calls to the connection's transactional
methods (begin, prepare, commit, rollback) will "bubble upward" to apply to the
distributed transaction shared by the group as a whole.
</p>
<p class="textParagraph">
Connections can be dynamically <code>add</code>ed and <code>remove</code>d
from a <code>ConnectionGroup</code> provided that neither the group nor
the connection itself has an unresolved transaction at the time of the
addition/removal.
</p>
<p class="textParagraph">
Never add two connections to the same database to the same
<code>ConnectionGroup</code>!
</p>
<br>
<br>
<hr>
<br>
<a name="adv_param_conv">
<h2>Parameter Conversion</h2>
</a>
<p class="textParagraph">
KInterbasDB converts bound parameters marked with a <code>?</code>
in SQL code in a standard way. However, the module also offers several
extensions to standard parameter binding, intended to make client code
more readable and more convenient to write.
</p>
<a name="adv_param_conv_implicit_from_string">
<h3>Implicit Conversion of Input Parameters from Strings</h3>
</a>
<p class="textParagraph">
The database engine treats most SQL data types in a weakly typed fashion:
the engine may attempt to convert the raw value to a different type,
as appropriate for the current context.
For instance, the SQL expressions <code>123</code> (integer)
and <code>'123'</code> (string) are treated equivalently when the value is
to be inserted into an <code>integer</code> field; the same applies when
<code>'123'</code> and <code>123</code> are to be inserted into a
<code>varchar</code> field.
</p>
<p class="textParagraph">
This weak typing model is quite unlike Python's dynamic yet strong typing.
Although weak typing is regarded with suspicion by most experienced
Python programmers, the database engine is in certain situations so
aggressive about its typing model that KInterbasDB must
<a href="http://sourceforge.net/tracker/index.php?func=detail&aid=531828&group_id=9913&atid=309913">compromise</a>
in order to remain an elegant means of programming the database engine.
</p>
<p class="textParagraph">
An example is the handling of "magic values" for date and time fields.
The database engine interprets string values such as
<code>'yesterday'</code>, <code>'now'</code>,
and <code>'current_timestamp'</code> as having special meaning in a
date/time context.
If KInterbasDB did not accept strings as the values of parameters destined
for storage in date/time fields, the resulting code would be awkward.
Consider the difference between the two Python snippets
below, which insert a row containing an integer and a timestamp into a
table defined with the following DDL statement:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">create</FONT> <FONT COLOR="#0000ff">table</FONT> test_table (i <FONT COLOR="#0000ff">int</FONT>, t <FONT COLOR="#0000ff">timestamp</FONT>)
</pre>
<pre class="codeBlock">
i <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#666600">1</FONT>
t <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'now'</FONT>
sqlWithMagicValues <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">"insert into test_table (i, t) values (?, '%s')"</FONT> <FONT COLOR="#7d0000">%</FONT> t
cur.<FONT COLOR="#000066">execute</FONT>( sqlWithMagicValues, (i,) )
</pre>
<pre class="codeBlock">
i <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#666600">1</FONT>
t <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'now'</FONT>
cur.<FONT COLOR="#000066">execute</FONT>( <FONT COLOR="#8f8c47">"insert into test_table (i, t) values (?, ?)"</FONT>, (i, t) )
</pre>
<p class="textParagraph">
If KInterbasDB did not support weak parameter typing, string parameters
that the database engine is to interpret as "magic values" would have to
be rolled into the SQL statement in a separate operation from the
binding of the rest of the parameters, as in the first Python
snippet above.
Implicit conversion of parameter values from strings allows the consistency
evident in the second snippet, which is both more readable and more general.
</p>
<p class="textParagraph">
It should be noted that KInterbasDB does not perform the conversion from
string itself. Instead, it passes that responsibility to the database
engine by changing the parameter metadata structure dynamically at the
last moment, then restoring the original state of the metadata structure
after the database engine has performed the conversion.
</p>
<p class="textParagraph">
A secondary benefit is that when one uses KInterbasDB to import large
amounts of data from flat files into the database, the incoming values
need not necessarily be converted to their proper Python types before
being passed to the database engine. Eliminating this
intermediate step may accelerate the import process considerably, although
other factors such as the chosen connection protocol and the deactivation
of indexes during the import are more consequential.
For bulk import tasks, the database engine's external tables also deserve
consideration. External tables can be used to suck semi-structured data
from flat files directly into the relational database without the
intervention of an ad hoc conversion program.
</p>
<a name="adv_param_conv_dynamic_type_translation">
<h3>Dynamic Type Translation</h3>
</a>
<p class="textParagraph">
Dynamic type translators are conversion functions registered by the
Python programmer to transparently convert database field values
to and from their internal representation.
</p>
<p class="textParagraph">
The client programmer can choose to ignore translators altogether, in
which case KInterbasDB will manage them behind the scenes.
Otherwise, the client programmer can use any of several
<a href="#adv_param_conv_dynamic_type_translation_tbl_ref_trans">standard type translators</a>
included with KInterbasDB, register custom translators, or
set the translators to <code>None</code> to deal directly with the
KInterbasDB-internal representation of the data type.
When translators have been registered for a specific SQL data
type, Python objects on their way into a database field of that type
will be passed through the input translator before they are presented
to the database engine; values on their way out of the database into
Python will be passed through the corresponding output translator.
Output and input translation for a given type is usually implemented
by two different functions.
</p>
<p class="textParagraph">
</p>
<a name="adv_param_conv_dynamic_type_translation_specifics">
<h4>Specifics of the Dynamic Type Translation API</h4>
</a>
<p class="textParagraph">
Translators are registered with the <code>[set|get]_type_trans_[in|out]</code>
methods of <code>Connection</code> and <code>Cursor</code>.
The <code>set_type_trans_[in|out]</code> methods accept a single argument:
a mapping of type name to translator.
The <code>get_type_trans[in|out]</code> methods return a copy of the
translation table. <code>Cursor</code>s inherit their
<code>Connection</code>'s translation settings, but can override
them without affecting the connection or other cursors (much as
subclasses can override the methods of their base classes).
</p>
<p class="textParagraph">
The following code snippet installs an input translator for fixed
point types (<code>NUMERIC</code>/<code>DECIMAL</code> SQL types)
into a connection:
</p>
<pre class="codeBlock" style="margin-top: 0px; margin-bottom: 0px;">
con.set_type_trans_in( {'FIXED': fixed_input_translator_function} )
</pre>
<p class="textParagraph">
The following method call retrieves the type translation table for
<code>con</code>:
</p>
<pre class="codeBlock" style="margin-top: 0px; margin-bottom: 0px;">
con.get_type_trans_in()
</pre>
<p class="textParagraph">
The method call above would return a translation table (dictionary) such as
this:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
{
'DATE': <function date_conv_in at 0x00920648>,
'TIMESTAMP': <function timestamp_conv_in at 0x0093E090>,
'FIXED': <function <lambda> at 0x00962DB0>,
'TIME': <function time_conv_in at 0x009201B0>
}
</pre>
<p class="textParagraph">
Notice that although the sample code registered only one type
translator, there are four listed in the mapping returned by the
<code>get_type_trans_in</code> method. KInterbasDB itself uses
dynamic type translation to implement <code>mx.DateTime</code>-based
date/time I/O, and to implement the deprecated
<code>Connection.precision_mode</code> API.
For the source code locations of KInterbasDB's reference translators,
see the
<a href="#adv_param_conv_dynamic_type_translation_tbl_ref_trans">table</a>
in the next section.
The <code>Connection.precision_mode</code> API is deprecated because
using it in combination with dynamic type translation is error-prone.
KInterbasDB itself installs new dynamic type translators when the value
of <code>Connection.precision_mode</code> is changed; if the programmer
has previously registered input or output translators for
<code>'FIXED'</code> types, those translators will be overwritten.
</p>
<p class="textParagraph">
In the sample above, a translator is registered under the key
<code>'FIXED'</code>, but Firebird has no SQL data type named
<code>FIXED</code>. The following table lists the names of the
database engine's SQL data types in the left column, and the
corresponding key under which client programmers can register
translators in the right column.
</p>
<table style="margin-left: 2em;">
<tr>
<td style="font-size: 105%; font-style: italic; font-weight: bold;">
<a name="adv_param_conv_dynamic_type_translation_tbl_trans_keys">
Mapping of SQL Data Type Names to Translator Keys
</a>
</td>
</tr>
<tr>
<td>
<table border="1">
<thead style="background-color: #EEEEEE; font-weight: bold;">
<tr>
<td style="width: 9em;">SQL Type(s)</td>
<td>Translator Key</td>
</tr>
</thead>
<tr>
<td style="vertical-align: top;">
<code>CHAR</code>/<code>VARCHAR</code>
</td>
<td>
<code>'TEXT'</code>
<span style="font-size: 80%;">for fields with charsets
<code>NONE</code>, <code>OCTETS</code>, or <code>ASCII</code></span>
<br>
<code>'TEXT_UNICODE'</code>
<span style="font-size: 80%;">for all other charsets</span>
</td>
</tr>
<tr>
<td><code>BLOB</code></td>
<td><code>'BLOB'</code></td>
</tr>
<tr>
<td><code>SMALLINT/INTEGER/BIGINT</code></td>
<td><code>'INTEGER'</code></td>
</tr>
<tr>
<td><code>FLOAT</code>/<code>DOUBLE PRECISION</code></td>
<td><code>'FLOATING'</code></td>
</tr>
<tr>
<td><code>NUMERIC</code>/<code>DECIMAL</code></td>
<td><code>'FIXED'</code></td>
</tr>
<tr>
<td><code>DATE</code></td>
<td><code>'DATE'</code></td>
</tr>
<tr>
<td><code>TIME</code></td>
<td><code>'TIME'</code></td>
</tr>
<tr>
<td><code>TIMESTAMP</code></td>
<td><code>'TIMESTAMP'</code></td>
</tr>
</table>
</td>
</tr>
</table>
<a name="adv_param_conv_dynamic_type_translation_consequences">
<h4>Consequences of the Availability of Dynamic Type Translation in KInterbasDB</h4>
</a>
<p class="textParagraph">
Dynamic type translation has eliminated KInterbasDB's compile-time
dependency on <code>mx.DateTime</code>. Although KInterbasDB will continue
to use <code>mx.DateTime</code> as its default date/time representation
for the sake of backward compatibility, dynamic type translation allows Python 2.3
users to conveniently deal with database date/time values in terms of the
new standard library module <code>datetime</code>, if they choose to.
</p>
<p class="textParagraph">
Dynamic type translation also allows <code>NUMERIC</code>/<code>DECIMAL</code>
values to be transparently represented as
<a href="#ref_fixedpoint"><code>fixedpoint.FixedPoint</code></a>
objects rather than scaled integers, which is much more convenient.
For backward compatibility, <code>NUMERIC</code>/<code>DECIMAL</code>
values are still represented by default as Python <code>float</code>s,
and the older API based on <code>Connection.precision_mode</code> is still
present. However, all of these representations are now implemented
"under the hood" via dynamic type translation.
</p>
<p class="textParagraph">
Reference implementations of all of the translators discussed above
are provided with KInterbasDB 3.1 and later, in these modules:
</p>
<table style="margin-left: 2em;">
<tr>
<td style="font-size: 105%; font-style: italic; font-weight: bold;">
<a name="adv_param_conv_dynamic_type_translation_tbl_ref_trans">
Reference Translators Included with KInterbasDB
</a>
</td>
</tr>
<tr>
<td>
<table border="1">
<thead style="background-color: #EEEEEE; font-weight: bold;">
<tr>
<td style="width: 11em;">SQL Type(s)</td>
<td style="width: 16em;">Python Type(s)</td>
<td style="width: 21em;">Reference Implementation In Module</td>
</tr>
</thead>
<tr>
<td rowspan="3"><code>NUMERIC</code>/<code>DECIMAL</code></td>
<td><code>float</code> <em>(imprecise)</em> (default)</td>
<td><code>kinterbasdb.typeconv_fixed_stdlib</code></td>
</tr>
<tr>
<td>scaled <code>int</code> <em>(precise)</em></td>
<td><code>kinterbasdb.typeconv_fixed_stdlib</code></td>
</tr>
<tr>
<td><code>fixedpoint.FixedPoint</code> <em>(precise)</em></td>
<td><code>kinterbasdb.typeconv_fixed_fixedpoint</code></td>
</tr>
<tr>
<td rowspan="2"><code>DATE</code>/<code>TIME</code>/<code>TIMESTAMP</code></td>
<td><code>mx.DateTime</code> (default)</td>
<td><code>kinterbasdb.typeconv_datetime_mx</code></td>
</tr>
<tr>
<td>Python 2.3+ <code>datetime</code></td>
<td><code>kinterbasdb.typeconv_datetime_stdlib</code></td>
</tr>
<tr>
<td>
<code>CHAR/VARCHAR</code>
<div style="font-size: 80%;">(with any character set except<br> NONE, OCTETS, ASCII)</div>
</td>
<td style="vertical-align: top;"><code>unicode</code></td>
<td style="vertical-align: top;"><code>kinterbasdb.typeconv_text_unicode</code></td>
</tr>
</table>
</td>
</tr>
</table>
<a name="adv_param_conv_dynamic_type_translation_writing_translators">
<h4>Writing Custom Translators</h4>
</a>
<p class="textParagraph">
Below is a table that specifies the required argument and return value
signatures of input and output converters for the various translator
keys.
Python's native types map perfectly to
<code>'TEXT'</code>,
<code>'TEXT_UNICODE'</code>,
<code>'BLOB'</code>,
<code>'INTEGER'</code>,
and <code>'FLOATING'</code>
types, so in those cases the translator signatures are very simple.
The signatures for
<code>'FIXED'</code>,
<code>'DATE'</code>,
<code>'TIME'</code>,
and <code>'TIMESTAMP'</code>
are not as simple because Python (before 2.3) lacks native types to
represent these values with both precision <em>and</em> convenience.
KInterbasDB handles <code>'FIXED'</code> values internally as scaled
integers; the date and time types as tuples.
</p>
<p class="textParagraph">
KInterbasDB itself uses translators implemented according to the rules in
the table below; the code for these reference translators can be found
in the Python modules named <code>kinterbasdb.typeconv_*</code>
(see the
<a href="#adv_param_conv_dynamic_type_translation_tbl_ref_trans">table</a>
in the previous section for details).
</p>
<table style="margin-left: 1em;">
<tr>
<td style="font-size: 105%; font-style: italic; font-weight: bold;">
<a name="adv_param_conv_dynamic_type_translation_tbl_signatures">
Signature Specifications for Input and Output Translators
</a>
</td>
</tr>
<tr>
<td>
<table border="1">
<thead style="background-color: #EEEEEE; font-weight: bold;">
<tr>
<td style="width: 6em;">Translator Key</td>
<td>Input Translator Argument/Return Value Signature</td>
<td>Output Translator Signature</td>
</tr>
</thead>
<tr>
<td>
<code>'TEXT'</code><br><br>
<span style="font-size: 80%">
(for <code>CHAR</code>/<code>VARCHAR</code> fields
with character sets <code>NONE</code>, <code>OCTETS</code>,
or <code>ASCII</code>)
</span>
</td>
<td>Args: a single Python <code>str</code>ing argument
(or <code>None</code>)
<br><br>
Returns: a single Python <code>str</code>ing
</td>
<td>Same signature as input translator, except that return value is not constrained.</td>
</tr>
<tr>
<td>
<code>'TEXT_UNICODE'</code><br><br>
<span style="font-size: 80%">
(for <code>CHAR</code>/<code>VARCHAR</code> fields
with character sets other than <code>NONE</code>, <code>OCTETS</code>,
or <code>ASCII</code>)
</span>
</td>
<td>Args:
a single Python 2-tuple argument containing a Python <code>unicode</code>
or <code>str</code> object (or <code>None</code>) in the first element;
the database character set code in the second element (the tuple is
of the form <code>(val, dbCharacterSetCode)</code>).
<br><br>
The database character set codes (which are integers) are defined on
pages 221-225 of the
<a href="#ref_ib6_docs">Interbase® 6 Data Definition Guide</a>.
The module <code>kinterbasdb.typeconv_text_unicode</code> contains a
dictionary named <code>DB_TO_PYTHON_ENCODING_MAP</code> that maps database
character set codes to Python codec names. For example, the database
character set <code>UNICODE_FSS</code> has code <code>3</code>;
<code>kinterbasdb.typeconv_text_unicode.DB_TO_PYTHON_ENCODING_MAP[3]</code>
is <code>'utf_8'</code>, the name of a Python codec that can be passed to
the <code>encode</code>/<code>decode</code> methods of
<code>unicode</code>/<code>str</code>.
<br><br>
Returns: a Python <code>str</code> object containing the
<span style="font-weight: bold; text-decoration: underline;">en</span>coded
representation of the incoming value (typically computed
via <code>val.encode</code>).
</td>
<td style="vertical-align: top;">
Args:
a single Python 2-tuple argument containing a Python <code>str</code>
object (or <code>None</code>) in the first element; the database
character set code in the second element (the tuple is
of the form <code>(val, dbCharacterSetCode)</code>).
<code>val</code> contains the encoded representation of the Unicode string.
<br><br>
Returns: a Python <code>unicode</code> object containing the
<span style="font-weight: bold; text-decoration: underline;">de</span>coded
representation of the outgoing value (typically computed
via <code>val.decode</code>).
</td>
</tr>
<tr>
<td><code>'BLOB'</code></td>
<td>Same signature as that of <code>'TEXT'</code>.</td>
<td>Same signature as input translator, except that return value is not constrained.</td>
</tr>
<tr>
<td><code>'INTEGER'</code></td>
<td>Args: a single Python <code>int</code> argument
(or <code>None</code>)
<br><br>
Returns: a single Python <code>int</code>
</td>
<td>Same signature as input translator, except that return value is not constrained.</td>
</tr>
<tr>
<td><code>'FLOATING'</code></td>
<td>Args: a single Python <code>float</code> argument
(or <code>None</code>)<br>
Returns: a single Python <code>float</code>
</td>
<td>Same signature as input translator, except that return value is not constrained.</td>
</tr>
<tr>
<td><code>'FIXED'</code></td>
<td>Args: a single Python 2-tuple argument containing a scaled Python
integer in the first element and the scale factor in the second
element (the tuple is of the form <code>(val, scale)</code>).
<br><br>
Returns: a single Python integer, scaled appropriately
</td>
<td>Same signature as input translator, except that return value is not constrained.</td>
</tr>
<tr>
<td><code>'DATE'</code></td>
<td>Args: an instance of the chosen date type (such as Python 2.3's
<code>datetime.date</code>) or <code>None</code>
<br><br>
Returns: a single Python 3-tuple of the form
<code>(year, month, day)</code>
</td>
<td>Args: a single Python 3-tuple of the form
<code>(year, month, day)</code>
(or <code>None</code> if the database field was <code>NULL</code>)
<br><br>
Return value is not constrained.
</td>
</tr>
<tr>
<td><code>'TIME'</code></td>
<td>Args: an instance of the chosen time type (such as Python 2.3's
<code>datetime.time</code>) or <code>None</code>
<br><br>
Returns: a single Python 3-tuple of the form
<code>(hour, minute, second)</code>
</td>
<td>Args: a single Python 3-tuple of the form
<code>(hour, minute, second)</code>
(or <code>None</code> if the database field was <code>NULL</code>).
<br><br>
Return value is not constrained.
</td>
</tr>
<tr>
<td><code>'TIMESTAMP'</code></td>
<td>Args: an instance of the chosen time type (such as Python 2.3's
<code>datetime.datetime</code>) or <code>None</code>
<br><br>
Returns: a single Python 6-tuple of the form
<code>(year, month, day, hour, minute, second)</code>
</td>
<td>Args: a single Python 3-tuple of the form
<code>(year, month, day, hour, minute, second)</code>.
(or <code>None</code> if the database field was <code>NULL</code>).
<br><br>
Return value is not constrained.
</td>
</tr>
</table>
</td>
</tr>
</table>
<br><br>
<a name="adv_param_conv_dynamic_type_translation_example">
<h4>Example Programs</h4>
</a>
<a name="adv_param_conv_dynamic_type_translation_example_datetime">
<h5>DATE/TIME/TIMESTAMP</h5>
</a>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> datetime <FONT COLOR="#32a532"># Python 2.3 standard library module</FONT>
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
<FONT COLOR="#0000ff">import</FONT> kinterbasdb.typeconv_datetime_stdlib <FONT COLOR="#0000ff">as</FONT> tc_dt
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">connect</FONT>(<FONT COLOR="#7d0000">*</FONT>args, <FONT COLOR="#7d0000">**</FONT>kwargs):
<FONT COLOR="#404040">"""</FONT>
<FONT COLOR="#404040"> This wrapper around kinterbasdb.connect creates connections that use</FONT>
<FONT COLOR="#404040"> the datetime module (which entered the standard library in Python 2.3)</FONT>
<FONT COLOR="#404040"> for both input and output of DATE, TIME, and TIMESTAMP database fields.</FONT>
<FONT COLOR="#404040"> This wrapper simply registers kinterbasdb's official date/time</FONT>
<FONT COLOR="#404040"> translators for the datetime module, which reside in the</FONT>
<FONT COLOR="#404040"> kinterbasdb.typeconv_datetime_stdlib module.</FONT>
<FONT COLOR="#404040"> An equivalent set of translators for mx.DateTime (which kinterbasdb</FONT>
<FONT COLOR="#404040"> uses by default for backward compatibility) resides in the</FONT>
<FONT COLOR="#404040"> kinterbasdb.typeconv_datetime_mx module.</FONT>
<FONT COLOR="#404040"> Note that because cursors inherit their connection's dynamic type</FONT>
<FONT COLOR="#404040"> translation settings, cursors created upon connections returned by this</FONT>
<FONT COLOR="#404040"> function will also use the datetime module.</FONT>
<FONT COLOR="#404040"> """</FONT>
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(<FONT COLOR="#7d0000">*</FONT>args, <FONT COLOR="#7d0000">**</FONT>kwargs)
con.<FONT COLOR="#000066">set_type_trans_in</FONT>({
<FONT COLOR="#8f8c47">'DATE'</FONT>: tc_dt.date_conv_in,
<FONT COLOR="#8f8c47">'TIME'</FONT>: tc_dt.time_conv_in,
<FONT COLOR="#8f8c47">'TIMESTAMP'</FONT>: tc_dt.timestamp_conv_in,
})
con.<FONT COLOR="#000066">set_type_trans_out</FONT>({
<FONT COLOR="#8f8c47">'DATE'</FONT>: tc_dt.date_conv_out,
<FONT COLOR="#8f8c47">'TIME'</FONT>: tc_dt.time_conv_out,
<FONT COLOR="#8f8c47">'TIMESTAMP'</FONT>: tc_dt.timestamp_conv_out,
})
<FONT COLOR="#0000ff">return</FONT> con
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">_test</FONT>():
con <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
<FONT COLOR="#32a532"># Retrieve the current timestamp of the database server.</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select current_timestamp from rdb$database"</FONT>)
curStamp <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()[<FONT COLOR="#666600">0</FONT>]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'The type of curStamp is'</FONT>, <FONT COLOR="#4343b8">type</FONT>(curStamp)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'curStamp is'</FONT>, curStamp
<FONT COLOR="#32a532"># Create a test table with a single TIMESTAMP column.</FONT>
con.<FONT COLOR="#000066">execute_immediate</FONT>(<FONT COLOR="#8f8c47">"recreate table test_stamp (a timestamp)"</FONT>)
con.<FONT COLOR="#000066">commit</FONT>()
<FONT COLOR="#32a532"># Insert a timestamp into the database, then retrieve it.</FONT>
py23StandardLibTimestamp <FONT COLOR="#7d0000">=</FONT> datetime.datetime.<FONT COLOR="#000066">now</FONT>()
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test_stamp values (?)"</FONT>, (py23StandardLibTimestamp,))
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select * from test_stamp"</FONT>)
curStamp <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()[<FONT COLOR="#666600">0</FONT>]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'The type of curStamp is'</FONT>, <FONT COLOR="#4343b8">type</FONT>(curStamp)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'curStamp is'</FONT>, curStamp
<FONT COLOR="#0000ff">if</FONT> <FONT COLOR="#0066a0">__name__</FONT> <FONT COLOR="#7d0000">==</FONT> <FONT COLOR="#8f8c47">'__main__'</FONT>:
<FONT COLOR="#000066">_test</FONT>()
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px; margin-bottom: 1.7em;">
The type of curStamp is <type 'datetime.datetime'>
curStamp is 2003-05-20 03:55:42
The type of stamp is <type 'datetime.datetime'>
stamp is 2003-05-20 03:55:42
</pre>
<a name="adv_param_conv_dynamic_type_translation_example_fixed">
<h5>FIXED</h5>
</a>
<pre class="codeBlock">
<FONT COLOR="#32a532"># Third-party fixedpoint module from</FONT>
<FONT COLOR="#32a532"># http://fixedpoint.sourceforge.net</FONT>
<FONT COLOR="#0000ff">import</FONT> fixedpoint <FONT COLOR="#0000ff">as</FONT> fp
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
<FONT COLOR="#0000ff">import</FONT> kinterbasdb.typeconv_fixed_fixedpoint <FONT COLOR="#0000ff">as</FONT> tc_fp
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">connect</FONT>(<FONT COLOR="#7d0000">*</FONT>args, <FONT COLOR="#7d0000">**</FONT>kwargs):
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(<FONT COLOR="#7d0000">*</FONT>args, <FONT COLOR="#7d0000">**</FONT>kwargs)
con.<FONT COLOR="#000066">set_type_trans_in</FONT>({
<FONT COLOR="#8f8c47">'FIXED'</FONT>: tc_fp.fixed_conv_in_precise,
})
con.<FONT COLOR="#000066">set_type_trans_out</FONT>({
<FONT COLOR="#8f8c47">'FIXED'</FONT>: tc_fp.fixed_conv_out_precise,
})
<FONT COLOR="#0000ff">return</FONT> con
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">_test</FONT>():
con <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
<FONT COLOR="#32a532"># Create a simple test table.</FONT>
con.<FONT COLOR="#000066">execute_immediate</FONT>(<FONT COLOR="#8f8c47">"recreate table test (a numeric(18,4))"</FONT>)
con.<FONT COLOR="#000066">commit</FONT>()
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
<FONT COLOR="#32a532"># Insert a FixedPoint object.</FONT>
inVal <FONT COLOR="#7d0000">=</FONT> fp.<FONT COLOR="#000066">FixedPoint</FONT>(<FONT COLOR="#8f8c47">'1.2345'</FONT>, <FONT COLOR="#666600">4</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'The type of inVal is '</FONT>, <FONT COLOR="#4343b8">type</FONT>(inVal)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'inVal is '</FONT>, inVal
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test values (?)"</FONT>, (inVal,))
<FONT COLOR="#32a532"># Retrieve the fixed point value.</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select a from test"</FONT>)
outVal <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()[<FONT COLOR="#666600">0</FONT>]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'The type of outVal is'</FONT>, <FONT COLOR="#4343b8">type</FONT>(outVal)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'outVal is'</FONT>, outVal
<FONT COLOR="#0000ff">if</FONT> <FONT COLOR="#0066a0">__name__</FONT> <FONT COLOR="#7d0000">==</FONT> <FONT COLOR="#8f8c47">'__main__'</FONT>:
<FONT COLOR="#000066">_test</FONT>()
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
The type of inVal is <class 'fixedpoint.FixedPoint'>
inVal is 1.2345
The type of outVal is <class 'fixedpoint.FixedPoint'>
outVal is 1.2345
</pre>
<br>
<a name="adv_param_conv_dynamic_type_translation_deferred_loading">
<h4>Deferred Loading of Dynamic Type Translators</h4>
</a>
<p class="textParagraph">
In versions of KInterbasDB prior to 3.1_pre5,
there was a difficulty due to backward compatibility constraints: KInterbasDB
would <em>unconditionally</em> import the <code>mx.DateTime</code> module
initially, even if the client programmer did not intend to use it.
Although the advent of dynamic type translation <em>technically</em> obviated
KInterbasDB's dependency on the <code>mx</code> package, KInterbasDB still
required that the <code>mx</code> package be available due to the
aforementioned unconditional import.
</p>
<p class="textParagraph">
KInterbasDB 3.1_pre5 introduces a workaround: it defers the loading of the
dynamic type translators so that the client programmer can forestall an
attempt to import third-party modules he has no intention of using.
The new <code>kinterbasdb.init</code> function takes a keyword argument
<code>type_conv</code>, which controls KInterbasDB's initial choice of
type translators. <code>type_conv</code> can be either an integer or an
object that has all of the attributes named in
<code>kinterbasdb.BASELINE_TYPE_TRANSLATION_FACILITIES</code> (an example
of such an object is the module <code>kinterbasdb.typeconv_backcompat</code>).
If <code>type_conv</code> is an integer, it will cause KInterbasDB to use one
of the following predefined type translator configurations:
</p>
<style type="text/css">
td.num {
font-size: 110%;
text-align: right;
vertical-align: top;
}
p.explanation {
margin-top: 0em;
margin-bottom: 0.4em;
}
</style>
<table border="1" style="margin-left: 1em;">
<tr style="background-color: #EEEEEE; font-weight: bold; vertical-align: top;">
<td>
<a name="adv_param_conv_dynamic_type_translation_tbl_convenience_codes">
<code>type_conv</code> integer "convenience code"
</a>
</td>
<td>Resulting translator configuration</td>
</tr>
<tr>
<td class="num">0</td>
<td>
<p class="explanation">
Minimal type translators that represent
date/time values as <code>tuple</code>s
and fixed point values as either
<code>float</code>s
or scaled <code>int</code>egers,
depending on the connection's
<a href="#db_api_extensions_and_caveats_precision_mode"><code>precision_mode</code></a>.
</p>
<p class="explanation">
Unicode values are not encoded or decoded automatically.
</p>
<p class="explanation">
Implemented by the <code>kinterbasdb.typeconv_naked</code> module.
</p>
</td>
</tr>
<tr>
<td class="num">
1
<br><span style="font-size: 85%">(default)</span>
</td>
<td>
<p class="explanation">
Backward-compatible type translators that represent
date/time values via the <code>mx.DateTime</code> module
and fixed point values as either
<code>float</code>s
or scaled <code>int</code>egers,
depending on the connection's
<a href="#db_api_extensions_and_caveats_precision_mode"><code>precision_mode</code></a>.
</p>
<p class="explanation">
Unicode values are not encoded or decoded automatically.
</p>
<p class="explanation">
Implemented by the <code>kinterbasdb.typeconv_backcompat</code> module.
</p>
<p class="explanation">
This configuration, which is the default, perfectly mimics
the type translation behavior of KInterbasDB 3.0.
</p>
</td>
</tr>
<tr>
<td class="num">100</td>
<td>
<p class="explanation">
This translator configuration, which is intended for use with Python 2.3
and later, represents
date/time values via the new standard library module <code>datetime</code>
and fixed point values via the third-party
<a href="#ref_fixedpoint"><code>fixedpoint</code></a>
module.
</p>
<p class="explanation">
Unicode values <em>are</em> encoded and decoded automatically
(see <a href="#faq_fep_unicode">this FAQ</a> for more info).
</p>
<p class="explanation">
Implemented by the <code>kinterbasdb.typeconv_23plus</code> module.
</p>
</td>
</tr>
</table>
<p class="textParagraph">
These integer type conversion codes are defined <em>solely</em> for convenience.
The same functionality is available via the object variant of
<code>type_conv</code>, but setting it up is more laborious for typical
translator configurations.
</p>
<p class="textParagraph">
It is anticipated that Python 2.4 or 2.5 will introduce into the standard
library a type capable of handling decimal fractions elegantly and precisely.
For convenience, a set of type translators will be added to the official
KInterbasDB distribution to support it. At that time, the combination of date/time handling via the
standard library <code>datetime</code> module and fixed point handling via
the standard library decimal module will become the "ideal" translator
configuration.
For the sake of backward compatibility, the integer convenience code
<code>type_conv=100</code> will not be changed to use the stdlib decimal
module; rather, a new code such as <code>type_conv=101</code> will be added.
</p>
<a name="adv_param_conv_dynamic_type_translation_deferred_loading_backcompat">
<h4 style="margin-left: 1em;">Deferred Loading: Backward Compatibility Issues</h4>
</a>
<p class="textParagraph">
The deferred type translator loading scheme introduced in KInterbasDB 3.1_pre5
goes to great lengths to maintain backward compatibility.
If the client programmer does not call <code>kinterbasdb.init</code>,
KInterbasDB will implicitly initialize itself in a backward-compatible manner
(<code>type_conv=1</code>) the first time one of its public functions is called
or one of its public classes is instantiated.
</p>
<p class="textParagraph">
The only known backward incompatibility is this:
the DB API type comparison singleton <code>DATETIME</code> will not compare
equal to any type until the <code>kinterbasdb.init</code> function has been
called (whether explicitly or implicitly).
After <code>kinterbasdb.init</code> has been called, <code>DATETIME</code>
will compare equal to the date, time, and timestamp types that were loaded.
</p>
<p class="textParagraph">
This issue should affect hardly any existing KInterbasDB-based programs.
</p>
<a name="adv_param_conv_dynamic_type_translation_deferred_loading_example">
<h4 style="margin-left: 1em;">Deferred Loading: Example Program That Uses <code>kinterbasdb.init</code></h4>
</a>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> datetime, os.path, string, sys
<FONT COLOR="#32a532"># Third-party fixedpoint module from http://fixedpoint.sourceforge.net</FONT>
<FONT COLOR="#0000ff">import</FONT> fixedpoint
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
kinterbasdb.<FONT COLOR="#000066">init</FONT>(type_conv<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#666600">100</FONT>)
<FONT COLOR="#32a532"># This program never imports mx.DateTime:</FONT>
<FONT COLOR="#0000ff">assert</FONT> <FONT COLOR="#8f8c47">'mx'</FONT> <FONT COLOR="#0000ff">not</FONT> <FONT COLOR="#0000ff">in</FONT> sys.modules
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">test</FONT>():
dbFilename <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'/temp/test_deferred_1.db'</FONT>
<FONT COLOR="#000066">prepareTestDatabase</FONT>(dbFilename)
<FONT COLOR="#32a532"># Connect with character set UNICODE_FSS, to match the default character set</FONT>
<FONT COLOR="#32a532"># of the test database.</FONT>
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT>dbFilename, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>,
charset<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'UNICODE_FSS'</FONT>
)
<FONT COLOR="#0000ff">assert</FONT> con.charset <FONT COLOR="#7d0000">==</FONT> <FONT COLOR="#8f8c47">'UNICODE_FSS'</FONT>
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
<FONT COLOR="#32a532"># Create a test table.</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#404040">"""</FONT>
<FONT COLOR="#404040"> create table test (</FONT>
<FONT COLOR="#404040"> a numeric(18,2),</FONT>
<FONT COLOR="#404040"> b date,</FONT>
<FONT COLOR="#404040"> c time,</FONT>
<FONT COLOR="#404040"> d timestamp,</FONT>
<FONT COLOR="#404040"> e varchar(50), /* Defaults to character set UNICODE_FSS. */</FONT>
<FONT COLOR="#404040"> f varchar(50), /* Defaults to character set UNICODE_FSS. */</FONT>
<FONT COLOR="#404040"> g varchar(50) character set ASCII</FONT>
<FONT COLOR="#404040"> )</FONT>
<FONT COLOR="#404040"> """</FONT>)
con.<FONT COLOR="#000066">commit</FONT>()
<FONT COLOR="#32a532"># Create an input value for each field in the test table.</FONT>
<FONT COLOR="#32a532"># Notice that the DB API date/time constructors in kinterbasdb generate</FONT>
<FONT COLOR="#32a532"># datetime-based objects instead of mx-based objects because of our earlier</FONT>
<FONT COLOR="#32a532"># call to kinterbasdb.init(type_conv=100).</FONT>
aIn <FONT COLOR="#7d0000">=</FONT> fixedpoint.<FONT COLOR="#000066">FixedPoint</FONT>(<FONT COLOR="#8f8c47">'4.53'</FONT>, <FONT COLOR="#666600">2</FONT>)
bIn <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">Date</FONT>(<FONT COLOR="#666600">2004</FONT>,<FONT COLOR="#666600">1</FONT>,<FONT COLOR="#666600">4</FONT>)
cIn <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">Time</FONT>(<FONT COLOR="#666600">16</FONT>,<FONT COLOR="#666600">27</FONT>,<FONT COLOR="#666600">59</FONT>)
dIn <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">Timestamp</FONT>(<FONT COLOR="#666600">2004</FONT>,<FONT COLOR="#666600">1</FONT>,<FONT COLOR="#666600">4</FONT>, <FONT COLOR="#666600">16</FONT>,<FONT COLOR="#666600">27</FONT>,<FONT COLOR="#666600">59</FONT>)
eIn <FONT COLOR="#7d0000">=</FONT> u<FONT COLOR="#8f8c47">'Dav\u2211'</FONT> <FONT COLOR="#32a532"># 'Dav' followed by N-Ary Summation symbol</FONT>
fIn <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'A plain ASCII string destined for a Unicode field.'</FONT>
gIn <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'Dave'</FONT>
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'-'</FONT> <FONT COLOR="#7d0000">*</FONT> <FONT COLOR="#666600">70</FONT>
inputValues <FONT COLOR="#7d0000">=</FONT> (aIn, bIn, cIn, dIn, eIn, fIn, gIn)
<FONT COLOR="#000066">reportValues</FONT>(<FONT COLOR="#8f8c47">'In'</FONT>, inputValues)
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into test values (?,?,?,?,?,?,?)"</FONT>, inputValues)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'-'</FONT> <FONT COLOR="#7d0000">*</FONT> <FONT COLOR="#666600">70</FONT>
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select a,b,c,d,e,f,g from test"</FONT>)
(aOut, bOut, cOut, dOut, eOut, fOut, gOut) <FONT COLOR="#7d0000">=</FONT> outputValues <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()
<FONT COLOR="#000066">reportValues</FONT>(<FONT COLOR="#8f8c47">'Out'</FONT>, outputValues)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'-'</FONT> <FONT COLOR="#7d0000">*</FONT> <FONT COLOR="#666600">70</FONT>
<FONT COLOR="#32a532"># Notice that all values made the journey to and from the database intact.</FONT>
<FONT COLOR="#0000ff">assert</FONT> inputValues <FONT COLOR="#7d0000">==</FONT> outputValues
<FONT COLOR="#32a532"># Notes about Unicode handling:</FONT>
<FONT COLOR="#32a532">#</FONT>
<FONT COLOR="#32a532"># Upon input, the Python unicode object eIn was encoded transparently for</FONT>
<FONT COLOR="#32a532"># storage in TEST.E (a VARCHAR field with character set UNICODE_FSS (that</FONT>
<FONT COLOR="#32a532"># is, UTF-8)). Upon output, the UNICODE_FSS value in TEST.E was decoded</FONT>
<FONT COLOR="#32a532"># transparently into the Python unicode object eOut.</FONT>
<FONT COLOR="#32a532">#</FONT>
<FONT COLOR="#32a532"># TEST.F accepted a Python str object even though it's a Unicode field.</FONT>
<FONT COLOR="#32a532"># The output value fOut is a Python unicode object rather than a str like</FONT>
<FONT COLOR="#32a532"># fIn, but</FONT>
<FONT COLOR="#0000ff">assert</FONT> fIn <FONT COLOR="#7d0000">==</FONT> fOut
<FONT COLOR="#32a532"># , even though</FONT>
<FONT COLOR="#0000ff">assert</FONT> <FONT COLOR="#4343b8">type</FONT>(fIn) <FONT COLOR="#7d0000">!=</FONT> <FONT COLOR="#4343b8">type</FONT>(fOut)
<FONT COLOR="#32a532">#</FONT>
<FONT COLOR="#32a532"># TEST.G, a VARCHAR field with an ASCII character set, accepted and returned</FONT>
<FONT COLOR="#32a532"># a Python str object, as ever.</FONT>
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">reportValues</FONT>(direction, values):
<FONT COLOR="#0000ff">for</FONT> (val, c) <FONT COLOR="#0000ff">in</FONT> <FONT COLOR="#4343b8">zip</FONT>(values, string.ascii_lowercase[:<FONT COLOR="#4343b8">len</FONT>(values)]):
varName <FONT COLOR="#7d0000">=</FONT> c <FONT COLOR="#7d0000">+</FONT> direction
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'%s has type %s, value\n %s'</FONT> <FONT COLOR="#7d0000">%</FONT> (varName, <FONT COLOR="#4343b8">type</FONT>(val), <FONT COLOR="#4343b8">repr</FONT>(val))
<FONT COLOR="#0000ff">def</FONT> <FONT COLOR="#000066">prepareTestDatabase</FONT>(dbFilename):
<FONT COLOR="#32a532"># Delete the test database if an old copy is already present.</FONT>
<FONT COLOR="#0000ff">if</FONT> os.path.<FONT COLOR="#000066">isfile</FONT>(dbFilename):
conOld <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT>dbFilename, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
conOld.<FONT COLOR="#000066">drop_database</FONT>()
<FONT COLOR="#32a532"># Create the test database afresh.</FONT>
kinterbasdb.<FONT COLOR="#000066">create_database</FONT>(<FONT COLOR="#404040">"""</FONT>
<FONT COLOR="#404040"> create database '%s'</FONT>
<FONT COLOR="#404040"> user 'sysdba' password 'pass'</FONT>
<FONT COLOR="#404040"> default character set UNICODE_FSS</FONT>
<FONT COLOR="#404040"> """</FONT> <FONT COLOR="#7d0000">%</FONT> dbFilename
)
<FONT COLOR="#0000ff">if</FONT> <FONT COLOR="#0066a0">__name__</FONT> <FONT COLOR="#7d0000">==</FONT> <FONT COLOR="#8f8c47">'__main__'</FONT>:
<FONT COLOR="#000066">test</FONT>()
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock">
----------------------------------------------------------------------
aIn has type <class 'fixedpoint.FixedPoint'>, value
FixedPoint('4.53', 2)
bIn has type <type 'datetime.date'>, value
datetime.date(2004, 1, 4)
cIn has type <type 'datetime.time'>, value
datetime.time(16, 27, 59)
dIn has type <type 'datetime.datetime'>, value
datetime.datetime(2004, 1, 4, 16, 27, 59)
eIn has type <type 'unicode'>, value
u'Dav\u2211'
fIn has type <type 'str'>, value
'A plain ASCII string destined for a Unicode field.'
gIn has type <type 'str'>, value
'Dave'
----------------------------------------------------------------------
aOut has type <class 'fixedpoint.FixedPoint'>, value
FixedPoint('4.53', 2)
bOut has type <type 'datetime.date'>, value
datetime.date(2004, 1, 4)
cOut has type <type 'datetime.time'>, value
datetime.time(16, 27, 59)
dOut has type <type 'datetime.datetime'>, value
datetime.datetime(2004, 1, 4, 16, 27, 59)
eOut has type <type 'unicode'>, value
u'Dav\u2211'
fOut has type <type 'unicode'>, value
u'A plain ASCII string destined for a Unicode field.'
gOut has type <type 'str'>, value
'Dave'
----------------------------------------------------------------------
</pre>
<br>
<a name="adv_param_conv_database_arrays">
<h3>Database Arrays</h3>
</a>
<p class="textParagraph">
KInterbasDB converts database arrays <em>from</em> Python sequences (except
strings) on input; <em>to</em> Python lists on output.
On input, the Python sequence must be nested appropriately if the array
field is multi-dimensional, and the incoming sequence must not
fall short of its maximum possible length (it will not be "padded"
implicitly--see below).
On output, the lists will be nested if the database array has multiple dimensions.
</p>
<p class="textParagraph">
Database arrays have no place in a purely relational data model, which
requires that data values be <em>atomized</em> (that is, every value stored
in the database must be reduced to elementary, non-decomposable parts).
The Interbase®/Firebird implementation of database arrays,
like that of most relational database engines that support this data type,
is fraught with limitations.
</p>
<p class="textParagraph">
First of all, the database engine claims to support up to 16 dimensions, but
actually malfunctions catastrophically above 10 (this bug is fixed in
Firebird 1.5-RC1 and later, thanks to Dmitry Yemanov).
</p>
<p class="textParagraph">
Database arrays are of fixed size, with a predeclared number of dimensions
and number of elements per dimension. Individual array elements cannot
be set to <code>NULL</code>/<code>None</code>,
so the mapping between Python lists (which have dynamic length and are
therefore <em>not</em> normally "padded" with dummy values) and non-trivial
database arrays is clumsy.
</p>
<p class="textParagraph">
Stored procedures cannot have array parameters.
</p>
<p class="textParagraph">
Finally, many interface libraries, GUIs, and even the isql command line
utility do not support database arrays.
</p>
<p class="textParagraph">
In general, it is preferable to avoid using database arrays unless you
have a compelling reason.
</p>
<a name="adv_param_conv_database_arrays_example">
<h4>Example Program</h4>
</a>
<p class="textParagraph">
The following example program inserts a 3-d array (nested Python list) into a
single database field, then retrieves it.
</p>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
con.<FONT COLOR="#000066">execute_immediate</FONT>(<FONT COLOR="#8f8c47">"recreate table array_table (a int[3,4])"</FONT>)
con.<FONT COLOR="#000066">commit</FONT>()
cur <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
arrayIn <FONT COLOR="#7d0000">=</FONT> [
[<FONT COLOR="#666600">1</FONT>, <FONT COLOR="#666600">2</FONT>, <FONT COLOR="#666600">3</FONT>, <FONT COLOR="#666600">4</FONT>],
[<FONT COLOR="#666600">5</FONT>, <FONT COLOR="#666600">6</FONT>, <FONT COLOR="#666600">7</FONT>, <FONT COLOR="#666600">8</FONT>],
[<FONT COLOR="#666600">9</FONT>,<FONT COLOR="#666600">10</FONT>,<FONT COLOR="#666600">11</FONT>,<FONT COLOR="#666600">12</FONT>]
]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'arrayIn: %s'</FONT> <FONT COLOR="#7d0000">%</FONT> arrayIn
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"insert into array_table values (?)"</FONT>, (arrayIn,))
cur.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select a from array_table"</FONT>)
arrayOut <FONT COLOR="#7d0000">=</FONT> cur.<FONT COLOR="#000066">fetchone</FONT>()[<FONT COLOR="#666600">0</FONT>]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'arrayOut: %s'</FONT> <FONT COLOR="#7d0000">%</FONT> arrayOut
con.<FONT COLOR="#000066">commit</FONT>()
</pre>
<p class="textParagraph">
Output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
arrayIn: [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
arrayOut: [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
</pre>
<br>
<hr>
<br>
<a name="adv_named_cursors">
<h2>Named Cursors</h2>
</a>
<p class="textParagraph">
The read/write property <code>Cursor.name</code> allows the Python
programmer to perform scrolling <code>UPDATE</code>s or <code>DELETE</code>s
via the "<code>SELECT ... FOR UPDATE</code>" syntax.
If you don't know what this means, refer to the section of the
<a href="#ref_ib6_docs">Interbase® 6 Language Reference</a>
that covers the <code>SELECT</code> statement (page 139).
The <code>Cursor.name</code> property can be ignored entirely if you don't
need to use it.
</p>
<a name="adv_named_cursors_example">
<h4>Example Program</h4>
</a>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
curScroll <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
curUpdate <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">cursor</FONT>()
curScroll.<FONT COLOR="#000066">execute</FONT>(<FONT COLOR="#8f8c47">"select city from addresses <strong>for update</strong>"</FONT>)
curScroll.name <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">'city_scroller'</FONT>
update <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#8f8c47">"update addresses set city=? <strong>where current of</strong> "</FONT> <FONT COLOR="#7d0000">+</FONT> curScroll.name
<FONT COLOR="#0000ff">for</FONT> (city,) <FONT COLOR="#0000ff">in</FONT> curScroll:
city <FONT COLOR="#7d0000">=</FONT> ... <FONT COLOR="#32a532"># make some changes to city</FONT>
curUpdate.<FONT COLOR="#000066">execute</FONT>( update, (city,) )
con.<FONT COLOR="#000066">commit</FONT>()
</pre>
<br>
<hr>
<br>
<a name="adv_prog_maint">
<h2>Programmatic Server, Database, and User Maintenance</h2>
</a>
<a name="adv_prog_maint_servapi">
<h3>Services API</h3>
</a>
<p class="textParagraph">
Database server maintenance tasks such as user management, load monitoring,
and database backup have traditionally been automated by scripting
the command-line tools <code>gbak</code>, <code>gfix</code>, <code>gsec</code>,
and <code>gstat</code>. These utilities are documented in the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a> (see
"Overview of command-line tools", page 28).
</p>
<p class="textParagraph">
The API presented to the client programmer by these utilities is inelegant
because they are, after all, command-line tools rather than native components
of the client language. To address this problem, Interbase® 6 introduced
a facility called the Services API, which exposes a uniform interface to the
administrative functionality of the traditional command-line tools.
</p>
<p class="textParagraph">
The native Services API, though consistent, is much lower-level than a
Pythonic API. If the native version were exposed directly, accomplishing
a given task would probably require more Python code than scripting the
traditional command-line tools. For this reason, KInterbasDB presents its own
abstraction over the native API via the <code>kinterbasdb.services</code>
module.
</p>
<p class="textParagraph">
</p>
<a name="adv_prog_maint_servapi_connect">
<h4>Establishing Services API Connections</h4>
</a>
<p class="textParagraph">
All Services API operations are performed in the context of a connection to
a specific database server, represented by the
<code>kinterbasdb.services.Connection</code> class.
<code>Connection</code>s are established by calling the
<code>kinterbasdb.services.connect</code> function, which accepts three keyword
arguments: <code>host</code>, <code>user</code>, and <code>password</code>.
<code>host</code> is the network name of the computer on which the database
server is running; <code>user</code> is the name of the database user under
whose authority the maintenance tasks are to be performed;
<code>password</code> is that
user's password. Since maintenance operations are most often initiated by an
administrative user on the same computer as the database server,
<code>host</code> defaults to the local computer, and <code>user</code>
defaults to <code>SYSDBA</code>.
</p>
<p class="textParagraph">
The three calls to <code>kinterbasdb.services.connect</code> in the following
program are equivalent:
</p>
<pre class="codeBlock" style="margin-top: 0px;">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
</pre>
<p class="textParagraph">
A no-argument <code>close</code> method is available to explicitly terminate
a <code>Connection</code>; if this is not invoked, the underlying connection
will be closed implicitly when the <code>Connection</code> object is garbage
collected.
</p>
<a name="adv_prog_maint_servapi_server_config">
<h4>Querying Server Configuration and Activity Levels</h4>
</a>
<h5 class="serviceManagerMethodName">Connection.getServiceManagerVersion</h5>
<p class="textParagraphTight">
To help client programs adapt to version changes, the service manager
exposes its version number as an integer:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getServiceManagerVersion</FONT>()
</pre>
<p class="textParagraphTight">
Output (on Firebird 1.5.0):
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
2
</pre>
<p class="textParagraph">
<code>kinterbasdb.services</code> is a thick wrapper of the Services
API that can shield its users from changes in the underlying C API, so this
method is unlikely to be useful to the typical Python client programmer.
</p>
<h5 class="serviceManagerMethodName">Connection.getServerVersion</h5>
<p class="textParagraphTight">
The <code>getServerVersion</code> method returns the server's version string:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getServerVersion</FONT>()
</pre>
<p class="textParagraphTight">
Output (on Firebird 1.5.0/Win32):
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
WI-V1.5.0.4290 Firebird 1.5
</pre>
<p class="textParagraph">
At first glance, the <code>kinterbasdb.services.Connection.getServerVersion</code>
method appears to duplicate the functionality of the
<code>kinterbasdb.Connection.server_version</code> property, but when
working with Firebird, there is a difference.
<code>kinterbasdb.Connection.server_version</code> is based
on a C API call (<code>isc_database_info</code>) that existed long
before the introduction of the Services API in Interbase® 6.
Some programs written before the advent of Firebird test the version number in the return value of
<code>isc_database_info</code>, and refuse to work if it indicates that the
server is too old. Since the first stable version of Firebird
was labeled <code>1.0</code>, this pre-Firebird version testing scheme
incorrectly concludes that (e.g.) Firebird 1.0 is older than
Interbase® 5.0.
</p>
<p class="textParagraph">
Firebird addresses this problem by making
<code>isc_database_info</code> return a "pseudo-Interbase®" version
number, whereas the Services API returns the true Firebird version, as shown:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'Interbase-compatible version string:'</FONT>, con.server_version
<FONT COLOR="#0000ff">import</FONT> kinterbasdb.services
svcCon <FONT COLOR="#7d0000">=</FONT> kinterbasdb.services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'Actual Firebird version string: '</FONT>, svcCon.<FONT COLOR="#000066">getServerVersion</FONT>()
</pre>
<p class="textParagraphTight">
Output (on Firebird 1.5.0/Win32):
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
Interbase-compatible version string: WI-V6.3.0.4290 Firebird 1.5
Actual Firebird version string: WI-V1.5.0.4290 Firebird 1.5
</pre>
<h5 class="serviceManagerMethodName">Connection.getArchitecture</h5>
<p class="textParagraphTight">
The <code>getArchitecture</code> method returns platform information for
the server, including hardware architecture and operating system family:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getArchitecture</FONT>()
</pre>
<p class="textParagraphTight">
Output (on Firebird 1.5.0/Windows 2000):
</p>
<pre class="programOutputBlockTight" style="margin-top: 0px;">
Firebird/x86/Windows NT
</pre>
<p class="textParagraphTight">
Unfortunately, the architecture string is almost useless because its format
is irregular and sometimes outright idiotic, as with Firebird 1.5.0 running
on x86 Linux:
</p>
<pre class="programOutputBlockTight" style="margin-top: 0px;">
Firebird/linux Intel
</pre>
<p class="textParagraphTight">
Magically, Linux becomes a hardware architecture, the ASCII store decides
to hold a 31.92% off sale, and Intel grabs an unfilled
niche in the operating system market.
</p>
<h5 class="serviceManagerMethodName">Connection.getHomeDir</h5>
<p class="textParagraphTight">
The <code>getHomeDir</code> method returns the equivalent of the
<code>RootDirectory</code> setting from <code>firebird.conf</code>:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getHomeDir</FONT>()
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Windows 2000 installation):
</p>
<pre class="programOutputBlockTight">
C:\dev\db\firebird150\
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Linux installation):
</p>
<pre class="programOutputBlockTight">
/opt/firebird/
</pre>
<h5 class="serviceManagerMethodName">Connection.getSecurityDatabasePath</h5>
<p class="textParagraphTight">
The <code>getSecurityDatabasePath</code> method returns the location of
the server's core security database, which contains user definitions and
such.
Interbase® and Firebird 1.0 named this database <code>isc4.gdb</code>,
while in Firebird 1.5 and later it's renamed to <code>security.fdb</code>:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getSecurityDatabasePath</FONT>()
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Windows 2000 installation):
</p>
<pre class="programOutputBlockTight">
C:\dev\db\firebird150\security.fdb
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Linux installation):
</p>
<pre class="programOutputBlockTight">
/opt/firebird/security.fdb
</pre>
<h5 class="serviceManagerMethodName">Connection.getLockFileDir</h5>
<p class="textParagraphTight">
The database engine
<a href="http://www.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_locking">uses a lock file</a>
to coordinate interprocess communication;
<code>getLockFileDir</code> returns the directory in which that file resides:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getLockFileDir</FONT>()
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Windows 2000 installation):
</p>
<pre class="programOutputBlockTight">
C:\dev\db\firebird150\
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Linux installation):
</p>
<pre class="programOutputBlockTight">
/opt/firebird/
</pre>
<h5 class="serviceManagerMethodName">Connection.getCapabilityMask</h5>
<p class="textParagraphTight">
The Services API offers "a bitmask representing the capabilities currently
enabled on the server", but the only available
<a href="#ref_ib6_docs">documentation</a>
for this bitmask suggests that it is "reserved for future implementation".
kinterbasdb exposes this bitmask as a Python <code>int</code> returned from
the <code>getCapabilityMask</code> method.
</p>
<h5 class="serviceManagerMethodName">Connection.getMessageFileDir</h5>
<p class="textParagraphTight">
To support internationalized error messages/prompts, the database engine stores
its messages in a file named <code>interbase.msg</code> (Interbase®
and Firebird 1.0) or <code>firebird.msg</code> (Firebird 1.5 and later).
The directory in which this file resides can be determined with the
<code>getMessageFileDir</code> method.
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getMessageFileDir</FONT>()
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Windows 2000 installation):
</p>
<pre class="programOutputBlockTight">
C:\dev\db\firebird150\
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Linux installation):
</p>
<pre class="programOutputBlockTight">
/opt/firebird/
</pre>
<h5 class="serviceManagerMethodName">Connection.getConnectionCount</h5>
<p class="textParagraph">
<code>getConnectionCount</code> returns the number of active connections to
databases managed by the server.
This count only includes <em>database</em>
connections (such as open instances of <code>kinterbasdb.Connection</code>),
not <em>services manager</em> connections
(such as open instances of <code>kinterbasdb.services.Connection</code>).
</p>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb, kinterbasdb.services
svcCon <FONT COLOR="#7d0000">=</FONT> kinterbasdb.services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'A:'</FONT>, svcCon.<FONT COLOR="#000066">getConnectionCount</FONT>()
con1 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'B:'</FONT>, svcCon.<FONT COLOR="#000066">getConnectionCount</FONT>()
con2 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'C:'</FONT>, svcCon.<FONT COLOR="#000066">getConnectionCount</FONT>()
con1.<FONT COLOR="#000066">close</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'D:'</FONT>, svcCon.<FONT COLOR="#000066">getConnectionCount</FONT>()
con2.<FONT COLOR="#000066">close</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'E:'</FONT>, svcCon.<FONT COLOR="#000066">getConnectionCount</FONT>()
</pre>
<p class="textParagraphTight">
On an otherwise inactive server, the example program generates the following
output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
A: 0
B: 1
C: 2
D: 1
E: 0
</pre>
<h5 class="serviceManagerMethodName">Connection.getAttachedDatabaseNames</h5>
<p class="textParagraphTight">
<code>getAttachedDatabaseNames</code> returns a list of the names of all
databases to which the server is maintaining at least one connection.
The database names are not guaranteed to be in any particular order.
</p>
<pre class="codeBlock">
<FONT COLOR="#0000ff">import</FONT> kinterbasdb, kinterbasdb.services
svcCon <FONT COLOR="#7d0000">=</FONT> kinterbasdb.services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'A:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con1 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'B:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con2 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test2.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'C:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con3 <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:C:/temp/test2.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'D:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con1.<FONT COLOR="#000066">close</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'E:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con2.<FONT COLOR="#000066">close</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'F:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
con3.<FONT COLOR="#000066">close</FONT>()
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'G:'</FONT>, svcCon.<FONT COLOR="#000066">getAttachedDatabaseNames</FONT>()
</pre>
<p class="textParagraphTight">
On an otherwise inactive server, the example program generates the following
output:
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
A: []
B: ['C:\\TEMP\\TEST.DB']
C: ['C:\\TEMP\\TEST2.DB', 'C:\\TEMP\\TEST.DB']
D: ['C:\\TEMP\\TEST2.DB', 'C:\\TEMP\\TEST.DB']
E: ['C:\\TEMP\\TEST2.DB']
F: ['C:\\TEMP\\TEST2.DB']
G: []
</pre>
<h5 class="serviceManagerMethodName">Connection.getLog</h5>
<p class="textParagraphTight">
The <code>getLog</code> method returns the contents of the server's log file
(named <code>interbase.log</code> by Interbase® and Firebird 1.0;
<code>firebird.log</code> by Firebird 1.5 and later):
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(host<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getLog</FONT>()
</pre>
<p class="textParagraphTight">
Output (on a particular Firebird 1.5.0/Windows 2000 installation):
</p>
<pre class="programOutputBlock" style="margin-top: 0px;">
STALIN (Client) Thu Jun 03 12:01:35 2004
INET/inet_error: send errno = 10054
STALIN (Client) Sun Jun 06 19:21:17 2004
INET/inet_error: connect errno = 10061
</pre>
<a name="adv_prog_maint_servapi_database_stats">
<h4>Querying Database Statistics</h4>
</a>
<h5 class="serviceManagerMethodName">Connection.getStatistics</h5>
<p class="textParagraphTight">
The <code>getStatistics</code> method returns a string containing a printout
in the same format as the output of the <code>gstat</code> command-line
utility. This method has one required parameter, the location of the database
on which to compute statistics, and five optional boolean parameters for
controlling the domain of the statistics.
</p>
<p class="textParagraph">
The section of the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a>
entitled "gstat command-line tool" (page 181)
documents <code>gstat</code>'s command-line options.
Rather than attempting to duplicate that documentation here,
we present a table of equivalence:
</p>
<table border="1" cellpadding="5">
<thead>
<tr style="background-color: #DEDEDE;">
<td><code>gstat</code> command-line option</td>
<td><code>kinterbasdb.services.Connection.getStatistics</code> boolean parameter</td>
</tr>
</thead>
<tr>
<td><code>-header</code></td>
<td><code>showOnlyDatabaseHeaderPages</code></td>
</tr>
<tr>
<td><code>-log</code></td>
<td><code>showOnlyDatabaseLogPages</code></td>
</tr>
<tr>
<td><code>-data</code></td>
<td><code>showUserDataPages</code></td>
</tr>
<tr>
<td><code>-index</code></td>
<td><code>showUserIndexPages</code></td>
</tr>
<tr>
<td><code>-system</code></td>
<td><code>showSystemTablesAndIndexes</code></td>
</tr>
</table>
<p class="textParagraph">
The following example program presents several <code>getStatistics</code>
calls and their <code>gstat</code>-command-line equivalents. In this
context, output is considered "equivalent" even if their are some whitespace
differences. When collecting textual output from the Services API,
kinterbasdb terminates lines with <code>\n</code> regardless of the platform's
convention; <code>gstat</code> is platform-sensitive.
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#32a532"># Equivalent to 'gstat -u sysdba -p masterkey C:/temp/test.db':</FONT>
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getStatistics</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>)
<FONT COLOR="#32a532"># Equivalent to 'gstat -u sysdba -p masterkey -header C:/temp/test.db':</FONT>
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getStatistics</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>, showOnlyDatabaseHeaderPages<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>)
<FONT COLOR="#32a532"># Equivalent to 'gstat -u sysdba -p masterkey -log C:/temp/test.db':</FONT>
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getStatistics</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>, showOnlyDatabaseLogPages<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>)
<FONT COLOR="#32a532"># Equivalent to 'gstat -u sysdba -p masterkey -data -index -system C:/temp/test.db':</FONT>
<FONT COLOR="#0000ff">print</FONT> con.<FONT COLOR="#000066">getStatistics</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>,
showUserDataPages<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>,
showUserIndexPages<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>,
showSystemTablesAndIndexes<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>
)
</pre>
<p class="textParagraphTight">
The output of the example program is not shown here because it is quite long.
</p>
<a name="adv_prog_maint_servapi_backup_restore">
<h4>Backup and Restoration</h4>
</a>
<p class="textParagraph">
KInterbasDB offers convenient programmatic control over database backup and
restoration via the <code>backup</code> and <code>restore</code> methods.
</p>
<p class="textParagraph">
At the time of this writing, released versions of Firebird/Interbase® do
not implement incremental backup, so we can simplistically define
<em>backup</em> as the process of generating and storing an archived replica
of a live database, and <em>restoration</em> as the inverse.
The backup/restoration process exposes numerous parameters, which are properly
documented in
Chapter 7 ("Database Backup and Restore") of the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a>.
The KInterbasDB API to these parameters is presented with minimal
documentation in the sample code below.
</p>
<a name="adv_prog_maint_servapi_backup_restore__backup">
<h5 class="serviceManagerMethodName">Connection.backup</h5>
</a>
<h5 class="serviceManagerMethod_Form">Simplest Form</h5>
<p class="textParagraphTight">
The simplest form of <code>backup</code> creates a single backup file
that contains everything in the database. Although the extension
<code>'.gbk'</code> is conventional, it is not required.
</p>
<pre class="codeBlockNoTop" style="margin-bottom: 0px;">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
backupLog <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">backup</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/test_backup.gbk'</FONT>)
<FONT COLOR="#0000ff">print</FONT> backupLog
</pre>
<p class="textParagraphTight" style="margin-bottom: 1em;">
In the example, <code>backupLog</code> is a string containing a
<code>gbak</code>-style log of the backup process. It is too long to
reproduce here.
</p>
<p class="textParagraph">
Although the return value of the <code>backup</code> method is a freeform
log string, <code>backup</code> will raise an exception if there is an error.
For example:
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
<FONT COLOR="#32a532"># Pass an invalid backup path to the engine:</FONT>
backupLog <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">backup</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>, <FONT COLOR="#8f8c47">'BOGUS/PATH/test_backup.gbk'</FONT>)
<FONT COLOR="#0000ff">print</FONT> backupLog
</pre>
<pre class="programOutputBlock" style="margin-top: 0px;">
Traceback (most recent call last):
File "adv_services_backup_simplest_witherror.py", line 5, in ?
backupLog = con.backup('C:/temp/test.db', 'BOGUS/PATH/test_backup.gbk')
File "C:\code\projects\kinterbasdb\Kinterbasdb-3.0\build\lib.win32-2.3\kinterbasdb\services.py", line 269, in backup
return self._actAndReturnTextualResults(request)
File "C:\code\projects\kinterbasdb\Kinterbasdb-3.0\build\lib.win32-2.3\kinterbasdb\services.py", line 613, in _actAndReturnTextualResults
self._act(requestBuffer)
File "C:\code\projects\kinterbasdb\Kinterbasdb-3.0\build\lib.win32-2.3\kinterbasdb\services.py", line 610, in _act
return _ksrv.action_thin(self._C_conn, requestBuffer.render())
kinterbasdb.OperationalError: (-902, '_kiservices could not perform the action: cannot open backup file BOGUS/PATH/test_backup.gbk. ')
</pre>
<h5 class="serviceManagerMethod_Form">Multifile Form</h5>
<p class="textParagraphTight">
The database engine has built-in support for splitting the backup into multiple
files, which is useful for circumventing operating system file size limits
or spreading the backup across multiple discs.
</p>
<p class="textParagraph">
KInterbasDB exposes this facility via the <code>Connection.backup</code>
parameters <code>destFilenames</code> and <code>destFileSizes</code>.
<code>destFilenames</code> (the second positional parameter of
<code>Connection.backup</code>) can be either a string (as in the example
above, when creating the backup as a single file) or a sequence of strings
naming each constituent file of the backup.
If <code>destFilenames</code> is a string-sequence with length <code>N</code>,
<code>destFileSizes</code> must be a sequence of integer file sizes
(in bytes) with length <code>N-1</code>. The database engine will constrain
the size of each backup constituent file named in
<code>destFilenames[:-1]</code> to the corresponding size specified in
<code>destFileSizes</code>; any remaining backup data will be placed in the
file name by <code>destFilenames[-1]</code>.
</p>
<p class="textParagraph">
Unfortunately, the database engine does not appear to expose any convenient
means of calculating the total size of a database backup before its creation.
The page size of the database and the number of pages in the database are
available via
<code>kinterbasdb.Connection.database_info(kinterbasdb.isc_info_page_size, 'i')</code>
and
<code>kinterbasdb.Connection.database_info(kinterbasdb.isc_info_db_size_in_pages, 'i')</code>,
respectively, but the size of the backup file is usually smaller than the size
of the database.
</p>
<p class="textParagraph">
There <em>should</em> be no harm in submitting too many constituent specifications; the
engine will write an empty header record into the excess constituents.
However, at the time of this writing, released versions of the database engine
hang the backup task if more than 11 constituents are specified (that is,
if <code>len(destFilenames) > 11</code>).
KInterbasDB does not prevent the programmer from submitting more than 11
constituents, but it does issue a warning.
</p>
<p class="textParagraph">
The following example program directs the engine to split the backup
of the database at <code>'C:/temp/test.db'</code> into
<code>'C:/temp/back01.gbk'</code>, a file 4096 bytes in size,
<code>'C:/temp/back02.gbk'</code>, a file 16384 bytes in size,
and <code>'C:/temp/back03.gbk'</code>, a file containing the remainder
of the backup data.
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
con.<FONT COLOR="#000066">backup</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test.db'</FONT>,
(<FONT COLOR="#8f8c47">'C:/temp/back01.gbk'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/back02.gbk'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/back03.gbk'</FONT>),
destFileSizes<FONT COLOR="#7d0000">=</FONT>(<FONT COLOR="#666600">4096</FONT>, <FONT COLOR="#666600">16384</FONT>)
)
</pre>
<h5 class="serviceManagerMethod_Form">Extended Options</h5>
<p class="textParagraphTight">
In addition to the three parameters documented previously
(positional <code>sourceDatabase</code>,
positional <code>destFilenames</code>,
and keyword <code>destFileSizes</code>),
the <code>Connection.backup</code> method accepts six boolean parameters
that control aspects of the backup process and the backup file output format.
These options are well documented beginning on page 149 of the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a>, so in this
document we present only a table of equivalence between the section caption in
the Interbase® 6 Operations Guide and the name of the boolean keyword
parameter:
</p>
<table border="1" style="margin-left: 1em;">
<thead>
<tr style="background-color: #DEDEDE;">
<td>IB6 Op. Guide Caption</td>
<td><code>Connection.backup</code><br>Parameter Name</td>
<td><code>Connection.backup</code><br>Parameter Default Value</td>
</tr>
</thead>
<tr>
<td>Format</td>
<td><code>transportable</code></td>
<td><code>True</code></td>
</tr>
<tr>
<td>Metadata Only</td>
<td><code>metadataOnly</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Garbage Collection</td>
<td><code>garbageCollect</code></td>
<td><code>True</code></td>
</tr>
<tr>
<td>Transactions in Limbo </td>
<td><code>ignoreLimboTransactions</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Checksums</td>
<td><code>ignoreChecksums</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Convert to Tables</td>
<td><code>convertExternalTablesToInternalTables </code></td>
<td><code>True</code></td>
</tr>
</table>
<a name="adv_prog_maint_servapi_backup_restore__restore">
<h5 class="serviceManagerMethodName" style="margin-top: 1.5em;">Connection.restore</h5>
</a>
<h5 class="serviceManagerMethod_Form">Simplest Form</h5>
<p class="textParagraphTight">
The simplest form of <code>restore</code> creates a single-file database,
regardless of whether the backup data were split across multiple files.
</p>
<pre class="codeBlockNoTop" style="margin-bottom: 0px;">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
restoreLog <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">restore</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test_backup.gbk'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/test_restored.db'</FONT>)
<FONT COLOR="#0000ff">print</FONT> restoreLog
</pre>
<p class="textParagraphTight" style="margin-bottom: 1em;">
In the example, <code>restoreLog</code> is a string containing a
<code>gbak</code>-style log of the restoration process. It is too long to
reproduce here.
</p>
<h5 class="serviceManagerMethod_Form">Multifile Form</h5>
<p class="textParagraphTight">
The database engine has built-in support for splitting the restored database
into multiple files, which is useful for circumventing operating system file
size limits or spreading the database across multiple discs.
</p>
<p class="textParagraph">
KInterbasDB exposes this facility via the <code>Connection.restore</code>
parameters <code>destFilenames</code> and <code>destFilePages</code>.
<code>destFilenames</code> (the second positional argument of
<code>Connection.restore</code>) can be either a string (as in the example
above, when restoring to a single database file) or a sequence of strings
naming each constituent file of the restored database.
If <code>destFilenames</code> is a string-sequence with length <code>N</code>,
<code>destFilePages</code> must be a sequence of integers with length
<code>N-1</code>. The database engine will constrain the size of each
database constituent file named in <code>destFilenames[:-1]</code> to the
corresponding page count specified in <code>destFilePages</code>; any
remaining database pages will be placed in the file name by
<code>destFilenames[-1]</code>.
</p>
<p class="textParagraph">
The following example program directs the engine to restore the backup file at
<code>'C:/temp/test_backup.gbk'</code> into a database with three constituent
files:
<code>'C:/temp/test_restored01.db'</code>,
<code>'C:/temp/test_restored02.db'</code>,
and
<code>'C:/temp/test_restored03.db'</code>.
The engine is instructed to place fifty user data pages in the first file,
seventy in the second, and the remainder in the third file. In practice, the
first database constituent file will be larger than
<code>pageSize*destFilePages[0]</code>, because metadata pages must also be
stored in the first constituent of a multifile database.
</p>
<pre class="codeBlockNoTop">
<FONT COLOR="#0000ff">from</FONT> kinterbasdb <FONT COLOR="#0000ff">import</FONT> services
con <FONT COLOR="#7d0000">=</FONT> services.<FONT COLOR="#000066">connect</FONT>(user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'masterkey'</FONT>)
con.<FONT COLOR="#000066">restore</FONT>(<FONT COLOR="#8f8c47">'C:/temp/test_backup.gbk'</FONT>,
(<FONT COLOR="#8f8c47">'C:/temp/test_restored01.db'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/test_restored02.db'</FONT>, <FONT COLOR="#8f8c47">'C:/temp/test_restored03.db'</FONT>),
destFilePages<FONT COLOR="#7d0000">=</FONT>(<FONT COLOR="#666600">50</FONT>, <FONT COLOR="#666600">70</FONT>),
pageSize<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#666600">1024</FONT>,
replace<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#0066a0">True</FONT>
)
</pre>
<h5 class="serviceManagerMethod_Form">Extended Options</h5>
<p class="textParagraphTight">
These options are well documented beginning on page 155 of the
<a href="#ref_ib6_docs">Interbase® 6 Operations Guide</a>, so in this
document we present only a table of equivalence between the section caption in
the Interbase® 6 Operations Guide and the name of the keyword
parameter to <code>Connection.restore</code>:
</p>
<table border="1" style="margin-left: 1em;">
<thead>
<tr style="background-color: #DEDEDE;">
<td>IB6 Op. Guide Caption</td>
<td><code>Connection.restore</code><br>Parameter Name</td>
<td><code>Connection.restore</code><br>Parameter Default Value</td>
</tr>
</thead>
<tr>
<td>Page Size</td>
<td><code>pageSize</code></td>
<td><code>[use server default]</code></td>
</tr>
<tr>
<td>Overwrite</td>
<td><code>replace</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Commit After Each Table</td>
<td><code>commitAfterEachTable</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Create Shadow Files</td>
<td><code>doNotRestoreShadows</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Deactivate Indexes</td>
<td><code>deactivateIndexes</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Validity Conditions</td>
<td><code>doNotEnforceConstraints</code></td>
<td><code>False</code></td>
</tr>
<tr>
<td>Use All Space</td>
<td><code>useAllPageSpace</code></td>
<td><code>False</code></td>
</tr>
</table>
<p class="textParagraph">
Two additional boolean parameters are not covered by the table above:
<code>cacheBuffers</code> and <code>accessModeReadOnly</code>.
<code>cacheBuffers</code> specifies the default number of cache pages for
the restored database. If left unspecified, <code>cacheBuffers</code> uses
the server default.
<code>accessModeReadOnly</code> (default <code>False</code>) specifies whether
the restored database is read-only (<code>True</code>) or
writable (<code>False</code>).
</p>
<a name="adv_prog_maint_servapi_database_maint">
<h4 style="margin-top: 3em;">Controlling Database Operating Modes, Sweeps, and Repair</h4>
</a>
<p class="textParagraph">
<span class="XXX_ADDRESS_THIS">(XXX: not yet documented)</span>
</p>
<a name="adv_prog_maint_servapi_users">
<h4>User Maintenance</h4>
</a>
<p class="textParagraph">
<span class="XXX_ADDRESS_THIS">(XXX: not yet documented)</span>
</p>
<br><br>
<a name="adv_prog_maint_database_info">
<h3>The <code>database_info</code> Method</h3>
</a>
<table border="1" class="memberDocFrame">
<tr>
<td class="memberDocHeader">
<code class="memberDocName">database_info</code>
<span class="memberDocNameCaption">(method; member of <code>kinterbasdb.Connection</code>)</span>
</td>
</tr>
<tr>
<td>
<p>
Wraps the Interbase® C API function <code>isc_database_info</code> .
For extensive documentation, see the
<a href="#ref_ib6_docs">Interbase® 6 API Guide</a>
section
entitled "Requesting information about an attachment" (page 51).
</p>
<p>
Note that this method is a <em>very thin</em> wrapper around
function <code>isc_database_info</code> .
This method does <em>not</em> attempt to interpret
its results except with regard to whether they are a string or an
integer.
</p>
<p>
For example, requesting <code>isc_info_user_names</code> with the
call<br>
<pre class="codeBlockInMemberDoc" style="margin-bottom: 0px;">con.<FONT COLOR="#000066">database_info</FONT>(kinterbasdb.isc_info_user_names, <FONT COLOR="#8f8c47">'s'</FONT>)</pre>
will return a binary string
containing a <em>raw</em> succession of length-name pairs. A thicker wrapper
might interpret those raw results and return a Python tuple, but it
would need to handle a multitude of special cases in order to cover
all possible <code>isc_info_*</code> items.
</p>
<p class="argHeader">Arguments:</p>
<ul class="argList">
<li>
<code>request</code> -
one of the <code>kinterbasdb.isc_info_*</code> constants.<br>
</li>
<li>
<code>result_type</code> -
must be either
<code>'s'</code> if you expect a string result, or
<code>'i'</code> if you expect an integer result.
</li>
</ul>
</td>
</tr>
</table>
<a name="adv_prog_maint_database_info_example">
<h4>Example Program</h4>
</a>
<pre class="codeBlock"><FONT COLOR="#0000ff">import</FONT> kinterbasdb
con <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">connect</FONT>(dsn<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'localhost:/temp/test.db'</FONT>, user<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'sysdba'</FONT>, password<FONT COLOR="#7d0000">=</FONT><FONT COLOR="#8f8c47">'pass'</FONT>)
<FONT COLOR="#32a532"># Retrieving an integer info item is quite simple.</FONT>
bytesInUse <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">database_info</FONT>(kinterbasdb.isc_info_current_memory, <FONT COLOR="#8f8c47">'i'</FONT>)
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'The server is currently using %d bytes of memory.'</FONT> <FONT COLOR="#7d0000">%</FONT> bytesInUse
<FONT COLOR="#32a532"># Retrieving a string info item is somewhat more involved, because the</FONT>
<FONT COLOR="#32a532"># information is returned in a raw binary buffer that must be parsed</FONT>
<FONT COLOR="#32a532"># according to the rules defined in the Interbase® 6 API Guide section</FONT>
<FONT COLOR="#32a532"># entitled "Requesting buffer items and result buffer values" (page 51).</FONT>
<FONT COLOR="#32a532">#</FONT>
<FONT COLOR="#32a532"># Often, the buffer contains a succession of length-string pairs</FONT>
<FONT COLOR="#32a532"># (one byte telling the length of s, followed by s itself).</FONT>
<FONT COLOR="#32a532"># Function kinterbasdb.raw_byte_to_int is provided to convert a raw</FONT>
<FONT COLOR="#32a532"># byte to a Python integer (see examples below).</FONT>
buf <FONT COLOR="#7d0000">=</FONT> con.<FONT COLOR="#000066">database_info</FONT>(kinterbasdb.isc_info_db_id, <FONT COLOR="#8f8c47">'s'</FONT>)
<FONT COLOR="#32a532"># Parse the filename from the buffer.</FONT>
beginningOfFilename <FONT COLOR="#7d0000">=</FONT> <FONT COLOR="#666600">2</FONT>
<FONT COLOR="#32a532"># The second byte in the buffer contains the size of the database filename</FONT>
<FONT COLOR="#32a532"># in bytes.</FONT>
lengthOfFilename <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">raw_byte_to_int</FONT>(buf[<FONT COLOR="#666600">1</FONT>])
filename <FONT COLOR="#7d0000">=</FONT> buf[beginningOfFilename:beginningOfFilename <FONT COLOR="#7d0000">+</FONT> lengthOfFilename]
<FONT COLOR="#32a532"># Parse the host name from the buffer.</FONT>
beginningOfHostName <FONT COLOR="#7d0000">=</FONT> (beginningOfFilename <FONT COLOR="#7d0000">+</FONT> lengthOfFilename) <FONT COLOR="#7d0000">+</FONT> <FONT COLOR="#666600">1</FONT>
<FONT COLOR="#32a532"># The first byte after the end of the database filename contains the size</FONT>
<FONT COLOR="#32a532"># of the host name in bytes.</FONT>
lengthOfHostName <FONT COLOR="#7d0000">=</FONT> kinterbasdb.<FONT COLOR="#000066">raw_byte_to_int</FONT>(buf[beginningOfHostName <FONT COLOR="#7d0000">-</FONT> <FONT COLOR="#666600">1</FONT>])
host <FONT COLOR="#7d0000">=</FONT> buf[beginningOfHostName:beginningOfHostName <FONT COLOR="#7d0000">+</FONT> lengthOfHostName]
<FONT COLOR="#0000ff">print</FONT> <FONT COLOR="#8f8c47">'We are connected to the database at %s on host %s.'</FONT> <FONT COLOR="#7d0000">%</FONT> (filename, host)
</pre>
<p class="textParagraph">
Sample output:
</p>
<pre class="programOutputBlock">
The server is currently using 8931328 bytes of memory.
We are connected to the database at C:\TEMP\TEST.DB on host STALIN.
</pre>
<p class="textParagraph">
As you can see, extracting data with the <code>database_info</code> function
is rather clumsy. The Services API (accessible to Python programmers via the
<a href="#adv_prog_maint_servapi"><code>kinterbasdb.services</code></a>
module) provides much higher-level
support for querying many database statistics, as well as numerous other
maintenance tasks.
</p>
<br>
<hr>
<br>
<a name="faq_fep">
<h2>Frequently Asked Questions and Frequently Encountered Pitfalls</h2>
</a>
<a name="faq_fep_result_set_fields_by_name">
<h3>Refer to Result Row Fields by Name Rather than Index</h3>
</a>
<p class="textParagraph">
Use the
<a href="#db_api_extensions_and_caveats_cursor_fetchonemap"><code>Cursor.fetch*map</code></a>
series of methods for traditional <code>fetch</code>es, or the
<code>Cursor.itermap</code> method to iterate over mappings rather than
sequences.
Example code appears in the Tutorial section entitled
<a href="#tutorial_execute_sql">"Executing SQL Statements"</a>.
</p>
<br><br>
<a name="faq_fep_fixed_point_precise">
<h3>Precise Fixed Point (<code>NUMERIC</code>/<code>DECIMAL</code>) Handling</h3>
</a>
<p class="textParagraph">
KInterbasDB's
<a href="#adv_param_conv_dynamic_type_translation">dynamic type translation</a>
allows database fixed point types to be handled both precisely and
conveniently, when combined with a full-featured fixed point data type
such as that implemented by the
<a href="#ref_fixedpoint"><code>fixedpoint</code></a>
module.
</p>
<p class="textParagraph">
An official implementation of dynamic type translators for the
<code>fixedpoint</code> module is distributed with KInterbasDB in the
<code>kinterbasdb.typeconv_fixed_fixedpoint</code> module; it can be
loaded conveniently using the features discussed in
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading">this section</a>.
Example programs appear
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading_example">here</a>
and
<a href="#adv_param_conv_dynamic_type_translation_example_fixed">here</a>.
</p>
<br><br>
<a name="faq_fep_datetime">
<h3>Dates and Times: egenix <code>mx.DateTime</code> vs. Python 2.3+ standard library <code>datetime</code></h3>
</a>
<p class="textParagraph">
KInterbasDB's
<a href="#adv_param_conv_dynamic_type_translation">dynamic type translation</a>
allows either of these date/time modules to be used with nearly equal convenience.
Example programs appear
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading_example">here</a>
and
<a href="#adv_param_conv_dynamic_type_translation_example">here</a>.
</p>
<p class="textParagraph">
Additionally, see
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading">this section</a>
for a discussion of how to conveniently load alternatives to
<code>mx.DateTime</code>.
</p>
<br><br>
<a name="faq_fep_unicode">
<h3>Unicode Fields and KInterbasDB</h3>
</a>
<p class="textParagraph">
By default, KInterbasDB handles Unicode input and output naively, leaving
responsibility for encoding and decoding to the client programmer.
</p>
<p class="textParagraph">
In version <code>3.1_pre7</code>, a dynamic type translation slot named
<code>'TEXT_UNICODE'</code> was introduced.
The <code>'TEXT_UNICODE'</code> translators are invoked for all
<code>CHAR</code> or <code>VARCHAR</code> fields except those with character
sets <code>NONE</code>, <code>OCTETS</code>, or <code>ASCII</code>.
</p>
<p class="textParagraph">
The most convenient way to handle Unicode with KInterbasDB is to combine
the <code>'TEXT_UNICODE'</code> slot with the official translator
implementation in the <code>kinterbasdb.typeconv_text_unicode</code> module.
This can be accomplished either manually, via
<code>[Connection|Cursor].set_type_trans_[in|out]</code>,
or by loading a predefined translator set with
<code>kinterbasdb.init</code>. At present, predefined set <code>100</code>
(as in <code>kinterbasdb.init(type_conv=100)</code>) is the only predefined
set that enables automagic Unicode handling.
</p>
<p class="textParagraph">
For more information, see the
<a href="#adv_param_conv_dynamic_type_translation_tbl_signatures">translator signature table</a>
and this
<a href="#adv_param_conv_dynamic_type_translation_deferred_loading_example">example program</a>.
</p>
<br><br>
<a name="faq_fep_embedded_using_with">
<h3>Using KInterbasDB with Embedded Firebird (Windows Only)</h3>
</a>
<p class="textParagraph">
The Firebird 1.5 Release Notes (<em>ReleaseNotes.pdf</em>, included with RC5
and later) describe Embedded Firebird as "a DLL that merges a single client
attachment with a Firebird Superserver for building very quick and efficient
stand-alone and briefcase applications."
Practically speaking, Embedded Firebird allows an application to use the
database engine without managing an external server process. This is ideal for
applications that will be distributed to end users, or that must be deployed
on operating systems that support background services poorly, such as Win9x.
</p>
<p class="textParagraph">
The KInterbasDB distribution linked against the Firebird 1.5 client library
fbclient.dll
(kinterbasdb-<em>V.V</em>.win32-FB1.5-py<em>V.V</em>)
works fine with Embedded Firebird. Only local-protocol connections
are supported, of course, and some of the standalone-server-oriented features
of the Services API are not supported.
</p>
<p class="textParagraph">
For generic Embedded Firebird configuration instructions, refer to the section
of the Firebird 1.5 Release Notes entitled
"Installing Embedded server from a zip kit"
(page 51 of the <em>ReleaseNotes.pdf</em> accompanying Firebird 1.5.0).
</p>
<p class="textParagraph">
Below are specific instructions for installing Embedded Firebird 1.5.0 for use
with Python 2.3 and KInterbasDB 3.1. These instructions assume that there
are no existing installations of Firebird or KInterbasDB on your system.
</p>
<ol>
<li>
<p class="textParagraph">
Extract the file
<em>kinterbasdb-V.V-win32-all-binaries-manual-pack.zip</em>
to a temporary directory. Copy the <em>kinterbasdb</em> directory
from <em>kinterbasdb-V.V-win32-all-binaries-pack\firebird-1.5\lib.win32-2.3</em>
to a directory on the PYTHONPATH of the python.exe you intend to use
Embedded Firebird with (e.g., <em>the-directory-of-python.exe\Lib\site-packages</em>).
</p>
</li>
<li>
<p class="textParagraph">
Embedded Firebird is determined to use the directory of the application's
executable as its root directory. For Python applications, this
is the directory in which python.exe (or pythonw.exe) resides. It is
supposedly possible to manually override the Embedded Firebird root
directory setting, but that option doesn't work consistently if esoteric
engine features are used.
</p>
<p class="textParagraph">
Extract <em>Firebird-1.5.0.4290_embed_win32.zip</em> to a temporary
directory. Copy the files
<em>fbembed.dll</em>,
<em>firebird.msg</em>,
and <em>ib_util.dll</em>
to the directory in which python.exe resides.
If you intend to use character sets other than ASCII, also copy
the <em>intl</em> subdirectory, which contains <em>fbintl.dll</em>.
</p>
</li>
<li>
<p class="textParagraph">
Rename <em>fbembed.dll</em> to <em>fbclient.dll</em>.
</p>
<p class="textParagraph">
You should now
have the following file structure:
<pre class="codeBlock" style="margin-top: 0px;">
the-directory-of-python.exe\
[python.exe, and other Python-related files]
fbclient.dll
firebird.msg
ib_util.dll
intl\ <--only necessary if using character sets other than ASCII
fbintl.dll <--^
</pre>
</p>
</li>
<li>
<p class="textParagraph">
Run your KInterbasDB-based Python application. The database engine is
"embedded" within the same process as your application; no external server
process is necessary, and no code changes are required.
</p>
</li>
</ol>
<br><br>
<a name="faq_fep_services_api_classic_embedded">
<h3>Services API with the Classic and Embedded Server Architectures</h3>
</a>
<p class="textParagraph">
Firebird's Classic architecture provides only crippled support for the Services
API; the Embedded architecture provides none at all.
Of course KInterbasDB's Services API support is subject to the constraints of
the server architecture to which it connects.
</p>
<br><br>
<a name="faq_fep_zope_using_with">
<h3>Using KInterbasDB with Zope</h3>
</a>
<p class="textParagraph">
There exist at least two Zope adapters based on KInterbasDB; see the
<a href="links.html#zope">links page</a>.
</p>
<br><br>
<br>
<hr>
<br>
<a name="references">
<h2>References (External Links)</h2>
</a>
<ul>
<li>
<a name="ref_fb_docs_directory" href="http://www.firebirdsql.org/index.php?op=doc">Firebird Documentation</a>
(directory of links)
</li>
<li>
<a name="ref_ib6_docs" href="http://www.firebirdsql.org/index.php?op=doc&id=userdoc">Interbase® 6 Documentation</a>
(including the SQL Language Reference, the Data Definition Guide
and the API Guide).
Although this documentation was written for Interbase® 6, it also
applies to Firebird.
</li>
<li><a name="ref_fixedpoint"><a href="http://fixedpoint.sourceforge.net">fixedpoint module</a>
Precise, convenient representation of fixed point values such as those
stored in <code>DECIMAL</code>/<code>NUMERIC</code> fields in Firebird.
</li>
<li>
<a name="ref_kidb_links" href="links.html">KInterbasDB links page</a> A directory of links
to software and documentation useful in conjunction with KInterbasDB.
</li>
</ul>
<br>
<hr>
<br>
<a name="feedback">
<h2>Feedback</h2>
</a>
<p class="textParagraph">
Send feedback about this documentation or the KInterbasDB code to the author
of the current versions of both,
<a href="mailto:woodsplitter@rocketmail.com">David Rushby</a>.
</p>
<br>
<hr>
<br>
<a href="index.html">Overall Table of Contents</a>
<a href="#toc">Usage Guide Table of Contents</a>
<a href="#top">Top of This Page</a>
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