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<title>GDA_TYPE_NULL: GNOME Data Access 5 manual</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id-1.2.10.3"></a>GDA_TYPE_NULL</h2></div></div></div>
<p>
Previous versions of <span class="application">Libgda</span> represented SQL NULL values as a <a href="/usr/share/gtk-doc/html/gobject/gobject-Generic-values.html#GValue">GValue</a> completely filled
with zeros (i.e. of type G_TYPE_INVALID), and GDA_TYPE_NULL was thus equivalent to G_TYPE_INVALID.
</p>
<p>
This new version introduces a new specific type for the same GDA_TYPE_NULL (which means
GDA_TYPE_NULL no longer equals G_TYPE_INVALID). The most common sources of errors brought by this
change are:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>if you used <a href="/usr/share/gtk-doc/html/gobject/gobject-Generic-values.html#g-value-init">g_value_init()</a> on a
value of type GDA_TYPE_NULL, then you'll have to eight clear the value first, or replace
that call with a call to <a class="link" href="libgda-5.0-Gda-Value.html#gda-value-reset-with-type" title="gda_value_reset_with_type ()">gda_value_reset_with_type()</a></p></li>
<li class="listitem"><p>the <a class="link" href="libgda-5.0-Utility-functions.html#gda-g-type-from-string" title="gda_g_type_from_string ()">gda_g_type_from_string()</a> function
now returns G_TYPE_INVALID if it does not know how to interpret the argument, so testing the return
value now also involves testing for the G_TYPE_INVALID value.</p></li>
<li class="listitem"><p>creating a GValue using <a href="/usr/share/gtk-doc/html/glib/glib-Memory-Allocation.html#g-new0">g_new0()</a> resulted
in a GDA_TYPE_NULL value, which is not longer the case; the value needs to be initialized
with a call to <a href="/usr/share/gtk-doc/html/gobject/gobject-Generic-values.html#g-value-init">g_value_init()</a></p></li>
<li class="listitem"><p>testing for NULL values using G_IS_VALUE does not work anymore, you'll have to
replace them with <a class="link" href="libgda-5.0-Gda-Value.html#GDA-VALUE-HOLDS-NULL:CAPS" title="GDA_VALUE_HOLDS_NULL()">GDA_VALUE_HOLDS_NULL()</a></p></li>
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