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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>GNOME Data Access 5 manual: Methods - DML queries</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id-1.9.7.11"></a>Methods - DML queries</h2></div></div></div>
<p>
      This group of virtual methods is related to executing SQL queries of any kind. <span class="application">Libgda</span> imposes that SQL
      statements be converted to one or more <a class="link" href="GdaStatement.html" title="GdaStatement">GdaStatement</a> object(s), each
      GdaStatement object containing exactly one SQL statement (usually terminated
      by a semi colon). Each GdaStatement can then be prepared and/or executed individually.
    </p>
<p>
      Creating a <a class="link" href="GdaStatement.html" title="GdaStatement">GdaStatement</a> object from some SQL is the job of a
      <a class="link" href="GdaSqlParser.html" title="GdaSqlParser">GdaSqlParser</a> object.
    </p>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.9.7.11.4"></a>create_parser()</h3></div></div></div>
<p>
	This method instantiates a <a class="link" href="GdaSqlParser.html" title="GdaSqlParser">GdaSqlParser</a> object which is
	adapted to the database's specific SQL dialect. If the provider does not implement its own parser,
	then this method should not be implemented.
      </p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.9.7.11.5"></a>statement_to_sql()</h3></div></div></div>
<p>
	This method converts a <a class="link" href="GdaStatement.html" title="GdaStatement">GdaStatement</a> object to its SQL representation. It should be
	implemented only if the default rendering is incorrect (to support some SQL specific dialect). The rendering process
	is decomposed into several rendering methods, and it is possible to override only some of the methods (see the
	PostgreSQL's implementation as an example).
      </p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.9.7.11.6"></a>statement_prepare()</h3></div></div></div>
<p>
	This method requests that a <a class="link" href="GdaStatement.html" title="GdaStatement">GdaStatement</a> object be prepared for a future execution.
	It is called when <a class="link" href="GdaConnection.html#gda-connection-statement-prepare" title="gda_connection_statement_prepare ()">gda_connection_statement_prepare()</a> is called.
      </p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.9.7.11.7"></a>statement_execute() - mandatory</h3></div></div></div>
<p>
	This method actually executes a query represented by a <a class="link" href="GdaStatement.html" title="GdaStatement">GdaStatement</a> object. See
	<a class="link" href="GdaConnection.html#gda-connection-statement-execute" title="gda_connection_statement_execute ()">gda_connection_statement_execute()</a> for more information, note that
	this method is also always the one called when any of the gda_connection_statement_execute*() methods are called.
      </p>
<p>
	A non NULL <em class="parameter"><code>exec_cb</code></em> parameter specifies that the user requests an asynchronous execution: the
	function has to return the NULL value immediately (it must not be blocking), and the <em class="parameter"><code>task_id</code></em>
	parameter must be set to contain a provider specific task ID.
	The <em class="parameter"><code>exec_cb</code></em> parameter points to a callback function (specified by the
	<a class="link" href="GdaConnection.html" title="GdaConnection">GdaConnection</a>) which the provider has to call once the statement has been
	executed, using the same task ID which was defined when the statement_execute() function was called, and
	the <em class="parameter"><code>cb_data</code></em> specified when the statement_execute() function was called.
      </p>
<p>
	Note that if an asynchronous execution is requested, then the <em class="parameter"><code>stmt</code></em>, <em class="parameter"><code>params</code></em>,
	<em class="parameter"><code>col_types</code></em>, <em class="parameter"><code>last_inserted_row</code></em>, and <em class="parameter"><code>cb_data</code></em>
	parameters are supposed to exist and not be altered during the time the statement is executed (the
	<a class="link" href="GdaConnection.html" title="GdaConnection">GdaConnection</a> ensures this) which means it's not necessary to make copies
	of them during the execution.
      </p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.9.7.11.8"></a>handle_async()</h3></div></div></div>
<p>
        This method is called by <a class="link" href="GdaConnection.html#gda-connection-async-fetch-result" title="gda_connection_async_fetch_result ()">gda_connection_async_fetch_result().</a>
      </p>
<p>
	This method, if implemented, is called to give the database provider a chance to execute some code in case an
	asynchronous statement's execution has been requested. Often providers will send some data over the network to the
	database server when the statement_execute() is called, and implement this virtual function as a way to get
	some data from the database server to see if the execution is terminated.
      </p>
<p>
        This function must return FALSE in case an error occurs, and TRUE if no error occurred (even if nothing was to be done).
      </p>
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