============================
``pymssql`` module reference
============================

.. module:: pymssql

Complete documentation of ``pymssql`` module classes, methods and properties.

Module-level symbols
====================

.. data:: __version__

   pymssql version as an Unicode constant. E.g. ``u"2.1.1"``, ``u"2.2.0"``

.. data:: VERSION

   pymssql version in tuple form which is more easily handled (parse, compare)
   programmatically. E.g. ``(2, 1, 1)``, ``(2, 2, 0)``

   .. versionadded:: 2.2.0

.. data:: __full_version__

   pymssql version as an Unicode constant but including any (:pep:`440`)
   suffixes.  E.g. ``u"2.1.0.dev2"``, ``u"2.2.0.dev"``

Constants, required by the DB-API 2.0 specification:

.. data:: apilevel

   ``'2.0'`` -- ``pymssql`` strives for compliance with DB-API 2.0.

.. data:: paramstyle

   ``'pyformat'`` -- ``pymssql`` uses extended python format codes.

.. data:: threadsafety

   ``1`` -- Module may be shared, but not connections.

Functions
=========

.. function:: connect(server='.', user=None, password=None, database='', \
                      timeout=0, login_timeout=60, charset='UTF-8', \
                      as_dict=False, host='', appname=None, port='1433',\
                      conn_properties=None, autocommit=False, tds_version=None)

   Constructor for creating a connection to the database. Returns a
   :class:`Connection` object. Note that in most cases you will want to
   use keyword arguments, instead of positional arguments.

   :param str server: database host
   :param str user: database user to connect as
   :param str password: user's password
   :param str database: The database to initialize the connection with. By
                        default *SQL Server* selects the database which is set as
                        default for specific user
   :param int timeout: query timeout in seconds, default ``0`` (no timeout)
   :param int login_timeout: timeout for connection and login in seconds, default ``60``
   :param str charset: character set with which to connect to the database
   :param bool as_dict: Whether rows should be returned as dictionaries instead
                        of tuples. You can access columns by 0-based index or
                        by name. Please see :doc:`examples </pymssql_examples>`
   :param str host: Database host and instance you want to connect to. Valid
                    examples are:

                     * ``r'.\SQLEXPRESS'`` -- SQLEXPRESS instance on local machine (Windows only)
                     * ``r'(local)\SQLEXPRESS'`` -- same as above (Windows only)
                     * ``'SQLHOST'`` -- default instance at default port (Windows only)
                     * ``'SQLHOST'`` -- specific instance at specific port set up in freetds.conf (Linux/\*nix only)
                     * ``'SQLHOST,1433'`` -- specified TCP port at specified host
                     * ``'SQLHOST:1433'`` -- the same as above
                     * ``'SQLHOST,5000'`` -- if you have set up an instance to listen on port 5000
                     * ``'SQLHOST:5000'`` -- the same as above

                     ``'.'`` (the local host) is assumed if host is not provided.
   :keyword str appname: Set the application name to use for the connection
   :keyword str port: the TCP port to use to connect to the server
   :keyword conn_properties: SQL queries to send to the server upon connection
                             establishment. Can be a string or another kind of
                             iterable of strings.  Default value: See
                             :class:`_mssql.connect() <_mssql.MSSQLConnection>`
   :keyword bool autocommit: Whether to use default autocommiting mode or not
   :keyword str tds_version: TDS protocol version to use

   .. warning::
       Currently, setting *timeout* or *login_timeout* has a process-wide
       effect because the FreeTDS db-lib API functions used to implement such
       timeouts have a global effect.

   .. note::
       If you need to connect to Azure read the relevant :doc:`topic </azure>`.

   .. versionadded:: 2.1.1
       The ability to connect to Azure.

   .. versionadded:: 2.1.1
       The *conn_properties* parameter.

   .. versionadded:: 2.1.1
       The *autocommit* parameter.

   .. versionadded:: 2.1.2
       The *tds_version* parameter.

   .. versionchanged:: 2.2.0
       The default value of the *tds_version* parameter was changed to ``None``.
       In version 2.1.2 its default value was ``'7.1'``.

   .. warning::
     The *tds_version* parameter has a default value of ``None``. This means two
     things:

     #. You can't rely anymore in the old ``'7.1'`` default value and
     #. Now you'll need to either

       * Specify its value explicitly by passing a value for this parameter or
       * Configure it using facilities provided by FreeTDS (see `here
         <http://www.freetds.org/userguide/freetdsconf.htm#TAB.FREETDS.CONF>`_
         and `here <http://www.freetds.org/userguide/envvar.htm>`_)

     This might look cumbersome but at the same time means you can now fully
     configure the characteristics of a connection to SQL Server from Python
     code when using pymssql without using a stanza for the server in the
     ``freetds.conf`` file or even with no ``freetds.conf`` at all. Up to
     version 2.1.1 it simply wasn't possible to control the TDS protocol
     version, and in version 2.1.2 it was possible to set it but version 7.1 was
     used if not specified.

   .. warning::
     FreeTDS added sopport for TDS protocol version 7.3 in version 0.95. You
     need to be careful of not asking for TDS 7.3 if you know the undelying
     FreeTDS used by pymssql is version 0.91 as it won't raise any error nor
     keep you from passing such an invalid value.

   .. warning::
     FreeTDS added support for TDS protocol version 7.3 in version 0.95. You
     need to be careful of not asking for TDS 7.3 if you know the undelying
     FreeTDS used by pymssql is older as it won't raise any error nor keep you
     from passing such an invalid value.

.. function:: get_dbversion()

    Wrapper around DB-Library's ``dbversion()`` function which returns the
    version of FreeTDS (actually the version of DB-Lib) in string form. E.g.
    ``"freetds v0.95"``.

    Unfortunately 1) The value returned doesn't indicate minor revisions (e.g.
    ``v0.95.50``), 2) Its data type makes it harder to compare versions or
    handle it programmatically in other ways and 3) It hasn't been consistently
    updated through the FreeTDS release history.

    A pymssql extension to the DB-API 2.0.

.. function:: set_max_connections(number)

    Sets maximum number of simultaneous database connections allowed to be open
    at any given time. Default is 25.

    A pymssql extension to the DB-API 2.0.

.. function:: get_max_connections()

    Gets current maximum number of simultaneous database connections allowed to
    be open at any given time.

    A pymssql extension to the DB-API 2.0.

.. function:: set_wait_callback(wait_callback_callable)

    .. versionadded:: 2.1.0

    Allows pymssql to be used along cooperative multi-tasking systems and have
    it call a callback when it's waiting for a response from the server.

    The passed callback callable should receive one argument: The file
    descriptor/handle of the network socket connected to the server, so its
    signature must be::

        def wait_callback_callable(read_fileno):
            #...
            pass

    Its body should invoke the appropiate API of the multi-tasking framework you
    are using use that results in the current greenlet yielding the CPU to its
    siblings whilst there isn't incoming data in the socket.

    See the :doc:`pymssql examples document </pymssql_examples>` for a more
    concrete example.

    A pymssql extension to the DB-API 2.0.

``Connection`` class
====================

.. class:: Connection(user, password, host, database, timeout, \
                      login_timeout, charset, as_dict)

    This class represents an MS SQL database connection. You can create an
    instance of this class by calling constructor :func:`pymssql.connect()`.


Connection object properties
----------------------------

This class has no useful properties and data members.

Connection object methods
-------------------------

.. method:: Connection.autocommit(status)

   Where *status* is a boolean value. This method turns autocommit mode on or
   off.

   By default, autocommit mode is off, what means every transaction must
   be explicitly committed if changed data is to be persisted in the database.

   You can turn autocommit mode on, what means every single operation commits
   itself as soon as it succeeds.

   A pymssql extension to the DB-API 2.0.

.. method:: Connection.close()

   Close the connection.

.. method:: Connection.cursor()

   Return a cursor object, that can be used to make queries and fetch results
   from the database.

.. method:: Connection.commit()

   Commit current transaction. You must call this method to persist your data if
   you leave autocommit at its default value, which is ``False``.

   See also :doc:`pymssql examples </pymssql_examples>`.

.. method:: Connection.rollback()

   Roll back current transaction.

``Cursor`` class
================

.. class:: Cursor

This class represents a Cursor (in terms of Python DB-API specs) that is used to
make queries against the database and obtaining results. You create
``Cursor`` instances by calling :py:meth:`~Connection.cursor()` method on
an open :py:class:`Connection` connection object.

Cusor object properties
-----------------------

.. attribute:: Cursor.rowcount

   Returns number of rows affected by last operation. In case of ``SELECT``
   statements it returns meaningful information only after all rows have been
   fetched.

.. attribute:: Cursor.connection

   This is the extension of the DB-API specification. Returns a reference to the
   connection object on which the cursor was created.

.. attribute:: Cursor.lastrowid

   This is the extension of the DB-API specification. Returns identity value of
   last inserted row. If previous operation did not involve inserting a row into
   a table with identity column, ``None`` is returned.

.. attribute:: Cursor.rownumber

   This is the extension of the DB-API specification. Returns current 0-based
   index of the cursor in the result set.

Cusor object methods
--------------------

.. method:: Cursor.close()

   Close the cursor. The cursor is unusable from this point.

.. method:: Cursor.execute(operation)
            Cursor.execute(operation, params)

    *operation* is a string and *params*, if specified, is a simple value, a
    tuple, a dict, or ``None``.

    Performs the operation against the database, possibly replacing parameter
    placeholders with provided values. This should be preferred method of
    creating SQL commands, instead of concatenating strings manually, what makes
    a potential of `SQL Injection attacks`_. This method accepts formatting similar
    to Python's builtin :ref:`string interpolation operator
    <python:string-formatting>`. However, since formatting and type conversion is handled
    internally, only the ``%s`` and ``%d`` placeholders are supported. Both placeholders are
    functionally equivalent.

    Keyed placeholders are supported if you provide a dict for *params*.

    If you call ``execute()`` with one argument, the ``%`` sign loses its
    special meaning, so you can use it as usual in your query string, for
    example in ``LIKE`` operator. See the :doc:`examples </pymssql_examples>`.

    You must call :meth:`Connection.commit()` after ``execute()`` or your data
    will not be persisted in the database. You can also set
    ``connection.autocommit`` if you want it to be done automatically. This
    behaviour is required by DB-API, if you don't like it, just use the
    :mod:`_mssql` module instead.

.. method:: Cursor.executemany(operation, params_seq)

   *operation* is a string and *params_seq* is a sequence of tuples (e.g. a
   list). Execute a database operation repeatedly for each element in parameter
   sequence.

.. method:: Cursor.fetchone()

   Fetch the next row of a query result, returning a tuple, or a dictionary if
   as_dict was passed to ``pymssql.connect()``, or ``None`` if no more data is
   available. Raises ``OperationalError`` (:pep:`249#operationalerror`) if
   previous call to ``execute*()`` did not produce any result set or no call was
   issued yet.

.. method:: Cursor.fetchmany(size=None)

   Fetch the next batch of rows of a query result, returning a list of tuples,
   or a list of dictionaries if *as_dict* was passed to
   :func:`pymssql.connect()`, or an empty list if no more data is available. You
   can adjust the batch size using the *size* parameter, which is preserved
   across many calls to this method. Raises ``OperationalError``
   (:pep:`249#operationalerror`) if previous call to ``execute*()`` did not
   produce any result set or no call was issued yet.

.. method:: Cursor.fetchall()

   Fetch all remaining rows of a query result, returning a list of tuples, or a
   list of dictionaries if as_dict was passed to ``pymssql.connect()``, or an
   empty list if no more data is available. Raises ``OperationalError``
   (:pep:`249#operationalerror`) if previous call to ``execute*()`` did not
   produce any result set or no call was issued yet.

.. method:: Cursor.nextset()

   This method makes the cursor skip to the next available result set,
   discarding any remaining rows from the current set. Returns ``True`` value if
   next result is available, ``None`` if not.

.. method:: Cursor.__iter__()
            Cursor.next()

   These methods facilitate :ref:`Python iterator protocol <python:typeiter>`.
   You most likely will not call them directly, but indirectly by using
   iterators.

   A pymssql extension to the DB-API 2.0.

.. method:: Cursor.setinputsizes()
            Cursor.setoutputsize()

   These methods do nothing, as permitted by DB-API specs.

Exceptions
==========

.. exception:: StandardError

    Root of the exception hierarchy.

.. exception:: Warning

    Raised for important warnings like data truncations while inserting, etc. A
    subclass of :exc:`StandardError`.

.. exception:: Error

    Base class of all other error exceptions. You can use this to catch all
    errors with one single except statement. A subclass of :exc:`StandardError`.

.. exception:: InterfaceError

    Raised for errors that are related to the database interface rather than the
    database itself. A subclass of :exc:`Error`.

.. exception:: DatabaseError

    Raised for errors that are related to the database. A subclass of
    :exc:`Error`.

.. exception:: DataError

    Raised for errors that are due to problems with the processed data like
    division by zero, numeric value out of range, etc. A subclass of
    :exc:`DatabaseError`.

.. exception:: OperationalError

    Raised for errors that are related to the database's operation and not
    necessarily under the control of the programmer, e.g. an unexpected
    disconnect occurs, the data source name is not found, a transaction could
    not be processed, a memory allocation error occurred during processing, etc.
    A subclass of :exc:`DatabaseError`.

.. exception:: IntegrityError

    Raised when the relational integrity of the database is affected, e.g. a
    foreign key check fails. A subclass of :exc:`DatabaseError`.

.. exception:: InternalError

    Raised when the database encounters an internal error, e.g. the cursor is
    not valid anymore, the transaction is out of sync, etc. A subclass of
    :exc:`DatabaseError`.

.. exception:: ProgrammingError

    Raised for programming errors, e.g. table not found or already exists,
    syntax error in the SQL statement, wrong number of parameters specified,
    etc. A subclass of :exc:`DatabaseError`.

.. exception:: NotSupportedError

    Raised in case a method or database API was used which is not supported by
    the database, e.g. requesting a :meth:`~Connection.rollback()` on a
    connection that does not support transaction or has transactions turned off.
    A subclass of :exc:`DatabaseError`.

.. exception:: ColumnsWithoutNamesError

    Raised by :meth:`Cursor.execute` when ``as_dict=True`` has been specified
    to :func:`open <connect>` the :class:`connection <Connection>` and the
    query sent to the server doesn't involve columns names in its results.
    A subclass of :exc:`InterfaceError`.

    .. note::
        ``ColumnsWithoutNamesError`` isn't a PEP-249-mandated exception but
        rather a pymssql extension.

.. _SQL Injection attacks: http://en.wikipedia.org/wiki/SQL_injection