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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Processing queries</title>
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<div class="chapter" lang="en">
<div class="titlepage"><div><div><h2 class="title">
<a name="processing-queries"></a>Processing queries</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="sect1"><a href="processing-queries.html#id446644">Executing sentences</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="processing-queries.html#building-commands">Building commands</a></span></dt>
<dt><span class="sect2"><a href="processing-queries.html#making-queries">Making <span class="emphasis"><em>non queries</em></span></a></span></dt>
<dt><span class="sect2"><a href="processing-queries.html#normal-queries">Making normal queries</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="data-model.html">Managing <span class="emphasis"><em>data models</em></span></a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="data-model.html#data-model-table-access">Example using direct cell access</a></span></dt>
<dt><span class="sect2"><a href="data-model.html#data-model-row-access">Example using row access</a></span></dt>
<dt><span class="sect2"><a href="data-model.html#data-model-free">Freeing data models</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="manage-gdavalue.html">Managing values</a></span></dt>
</dl></div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id446644"></a>Executing sentences</h2></div></div></div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="building-commands"></a>Building commands</h3></div></div></div>
<p>
Before invoking a query you have to build the structure containing the
command and you can do this with <a class="link" href="libgda-gda-command.html#gda-command-new" title="gda_command_new ()">
<span class="emphasis"><em>gda_command_new ()</em></span></a>.
</p>
<p>
The command type we most commonly use is <a class="link" href="libgda-gda-command.html#GdaCommandType" title="enum GdaCommandType">GDA_COMMAND_TYPE_SQL</a> because we will only
focus on <a href="http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=SQL"><span class="acronym">SQL</span></a> queries<sup>[<a name="id446679" href="#ftn.id446679" class="footnote">3</a>]</sup>
</p>
<div class="programlistingco">
<pre class="programlisting">
typedef enum {
GDA_COMMAND_OPTION_IGNORE_ERRORS = 1,
GDA_COMMAND_OPTION_STOP_ON_ERRORS = 1 << 1,
GDA_COMMAND_OPTION_BAD_OPTION = 1 << 2
} <a class="link" href="libgda-gda-command.html#GdaCommandOptions" title="enum GdaCommandOptions">GdaCommandOptions</a>;
</pre>
<div class="calloutlist"><table border="0" summary="Callout list">
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/1.png" alt="1" border="0"></p></td>
<td valign="top" align="left"><p>
Ignores all errors and executes all sentences returning data models.
For failed sentences, it returns an empty data model.
</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/2.png" alt="2" border="0"></p></td>
<td valign="top" align="left"><p>
Stops when finding and error and doesn't return data models.
</p></td>
</tr>
</table></div>
</div>
<p>
Here you see an example of creating a command:
</p>
<div class="programlistingco">
<pre class="programlisting">
gint
execute_sql_non_query (GdaConnection *connection, const gchar * buffer)
{
GdaCommand *command;
gint number;
command = gda_command_new (buffer, GDA_COMMAND_TYPE_SQL, GDA_COMMAND_OPTION_STOP_ON_ERRORS);
number = gda_connection_execute_non_query (connection, command, NULL);
gda_command_free (command);
return (number);
}
</pre>
<div class="calloutlist"><table border="0" summary="Callout list">
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/1.png" alt="1" border="0"></p></td>
<td valign="top" align="left"><p>
Our function. You can give it several comma-separated sentences.
</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/2.png" alt="2" border="0"></p></td>
<td valign="top" align="left"><p>
We will see it <a class="link" href="processing-queries.html#making-queries" title="Making non queries">later</a>.
</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/3.png" alt="3" border="0"></p></td>
<td valign="top" align="left"><p>
It is a good practice to free the commands.
</p></td>
</tr>
</table></div>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="making-queries"></a>Making <span class="emphasis"><em>non queries</em></span>
</h3></div></div></div>
<p>
<span class="emphasis"><em>Non queries</em></span> are queries that does not return data, only the
number of rows affected, as a DELETE or an UPDATE. We use <a class="link" href="libgda-GdaConnection.html#gda-connection-execute-non-query" title="gda_connection_execute_non_query ()"><span class="emphasis"><em>
gda_connection_execute_non_query()</em></span></a>
</p>
<pre class="programlisting">
gint
execute_sql_non_query (GdaConnection *connection, const gchar * buffer)
{
GdaCommand *command;
gint number;
command = gda_command_new (buffer, GDA_COMMAND_TYPE_SQL, GDA_COMMAND_OPTION_STOP_ON_ERRORS);
number = gda_connection_execute_non_query (connection, command, NULL);
gda_command_free (command);
return (number);
}
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="normal-queries"></a>Making normal queries</h3></div></div></div>
<p>
Normal queries are queries that return data (<a class="link" href="data-model.html" title="Managing data models">data models</a>). You have two ways to do this:
</p>
<div class="itemizedlist"><ul type="disc">
<li><p>
<a class="link" href="libgda-GdaConnection.html#gda-connection-execute-single-command" title="gda_connection_execute_single_command ()">
gda_data_model_execute_single_command()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaConnection.html#gda-connection-execute-command" title="gda_connection_execute_command ()">
gda_data_model_execute_command()</a></p></li>
</ul></div>
<p>
You can use the first way when you want to invoke only a single command.
Second way is used to execute several comma-separated sentences. It is recommended
to use <a class="link" href="libgda-GdaConnection.html#gda-connection-execute-single-command" title="gda_connection_execute_single_command ()">
gda_connection_execute_single_command ()</a>. Here you see an
example:
</p>
<div class="programlistingco">
<pre class="programlisting">
gboolean
execute_sql_command (GdaConnection *connection, const gchar * buffer)
{
GdaCommand *command;
GList *list;
GList *node;
gboolean errors=FALSE;
GdaDataModel *dm;
command = gda_command_new (buffer, GDA_COMMAND_TYPE_SQL, GDA_COMMAND_OPTION_STOP_ON_ERRORS);
list = gda_connection_execute_command (connection, command, NULL);
if (list!=NULL)
for (node=g_list_first(list); node != NULL; node=g_list_next(node))
{
dm=(GdaDataModel *) node->data;
if (dm == NULL)
{
errors=TRUE;
}
else
{
show_table (dm);
g_object_unref(dm);
}
}
else
{
errors=TRUE;
}
gda_command_free (command);
return (errors);
}
</pre>
<div class="calloutlist"><table border="0" summary="Callout list">
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/1.png" alt="1" border="0"></p></td>
<td valign="top" align="left"><p>
Executes the query and obtains a list of <a class="link" href="data-model.html" title="Managing data models">data models</a>
</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left"><p><img src="images/callouts/2.png" alt="2" border="0"></p></td>
<td valign="top" align="left"><p>
Loop for moving through the list of data models. If you use <a class="link" href="libgda-GdaConnection.html#gda-connection-execute-single-command" title="gda_connection_execute_single_command ()">
gda_connection_execute_single_command()</a>, you should not need to use a loop,
because this function would return a <a class="link" href="data-model.html" title="Managing data models">data model</a>.
</p></td>
</tr>
</table></div>
</div>
</div>
</div>
<div class="footnotes">
<br><hr width="100" align="left">
<div class="footnote"><p><sup>[<a name="ftn.id446679" href="#id446679" class="para">3</a>] </sup>There are other command types, as <a href="http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=XML"><span class="acronym">XML</span></a> and so on.</p></div>
</div>
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