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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Managing data models</title>
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<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="data-model"></a>Managing <span class="emphasis"><em>data models</em></span>
</h2></div></div></div>
<p>
Each time we execute a normal query, we will obtain a <a class="link" href="libgda-GdaDataModel.html" title="GdaDataModel"><span class="emphasis"><em>GdaDataModel
</em></span></a> object, which is the way to see what the query returned. As
<a class="link" href="libgda-GdaDataModel.html" title="GdaDataModel">GdaDataModel</a> is an object, we can manage it with <a class="link" href="libgda-GdaDataModel.html" title="GdaDataModel">GdaDataModel</a> class.
</p>
<p>
Before continuing, we must say that it is possible to modify a data model, but as we
are accessing using <a href="http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=SQL"><span class="acronym">SQL</span></a>, it is not recommended to modify it, so modifications on the
database must be done using <a href="http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=SQL"><span class="acronym">SQL</span></a>.
</p>
<p>
Let's see the functions we need:
</p>
<div class="itemizedlist"><ul type="disc">
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-n-rows" title="gda_data_model_get_n_rows ()">gda_data_model_get_n_rows()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-n-columns" title="gda_data_model_get_n_columns ()">gda_data_model_get_n_columns()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-describe-column" title="gda_data_model_describe_column ()">gda_data_model_describe_column()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-column-title" title="gda_data_model_get_column_title ()">gda_data_model_get_column_title()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-column-position" title="gda_data_model_get_column_position ()">gda_data_model_get_column_position()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-row" title="gda_data_model_get_row ()">gda_data_model_get_row()</a></p></li>
<li><p>
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-value-at" title="gda_data_model_get_value_at ()">gda_data_model_get_value_at()</a></p></li>
<li><p>
<a class="link" href="libgda-gda-row.html#gda-row-get-value" title="gda_row_get_value ()">gda_row_get_value()</a></p></li>
</ul></div>
<p>
This functions are very easy to use, so let's see some clear
examples:
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="data-model-table-access"></a>Example using direct cell access</h3></div></div></div>
<p>
This function accesses the data model by directly accessing cells (using
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-value-at" title="gda_data_model_get_value_at ()">gda_data_model_get_value_at ()
</a>)
</p>
<div class="programlistingco">
<pre class="programlisting">
void
show_table (GdaDataModel * dm)
{
gint row_id;
gint column_id;
GdaValue *value;
for (column_id = 0; column_id < gda_data_model_get_n_columns (dm);
column_id++)
g_print("%s\t",gda_data_model_get_column_title (dm, column_id));
g_print("\n");
for (row_id = 0; row_id < gda_data_model_get_n_rows (dm); row_id++) {
for (column_id = 0; column_id < gda_data_model_get_n_columns (dm);
column_id++) {
char *str;
value = gda_data_model_get_value_at (dm, column_id, row_id);
str = gda_value_stringify (value);
g_print ("%s\t", str);
}
g_print("\n");
}
}
</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>
Loop for writing column names.
</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>
Double loop accessing values using
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-value-at" title="gda_data_model_get_value_at ()">gda_data_model_get_value_at ()
</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>
Data returned is a <a class="link" href="libgda-gda-value.html" title="gda-value">GdaValue</a> object.
</p></td>
</tr>
</table></div>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="data-model-row-access"></a>Example using row access</h3></div></div></div>
<p>
This function accesses the data model by accessing rows (using
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-row" title="gda_data_model_get_row ()">gda_data_model_get_row ()
</a> and
<a class="link" href="libgda-gda-row.html#gda-row-get-value" title="gda_row_get_value ()"> gda_row_get_value ()
</a>)
</p>
<div class="programlistingco">
<pre class="programlisting">
<a name="show_table2"></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>
Loop for writing column names.
</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>
Outer loop obtaining rows using
<a class="link" href="libgda-GdaDataModel.html#gda-data-model-get-row" title="gda_data_model_get_row ()">gda_data_model_get_row ()
</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>
Inner loop obtaining the value using
<a class="link" href="libgda-gda-row.html#gda-row-get-value" title="gda_row_get_value ()">gda_row_get_value ()
</a>. Notice that <a class="link" href="libgda-gda-row.html#gda-row-get-value" title="gda_row_get_value ()">gda_row_get_value ()</a>
returns a <span class="emphasis"><em>const <a class="link" href="libgda-gda-value.html" title="gda-value">GdaValue</a></em></span>, so we
do not have to free it.
</p></td>
</tr>
</table></div>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="data-model-free"></a>Freeing data models</h3></div></div></div>
<p>
When you finish using data models you must free it, but GdaDataModel class
does not have a function to do it, so you have to use <span class="emphasis"><em>g_object_unref
()</em></span>.
</p>
</div>
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