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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Blobs</title>
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<tr><td colspan="5" class="shortcuts">
<a href="#GdaBlobOp.synopsis" class="shortcut">Top</a>
                   | 
                  <a href="#GdaBlobOp.description" class="shortcut">Description</a>
                   | 
                  <a href="#GdaBlobOp.object-hierarchy" class="shortcut">Object Hierarchy</a>
</td></tr>
</table>
<div class="refentry">
<a name="GdaBlobOp"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="GdaBlobOp.top_of_page"></a>Blobs</span></h2>
<p>Blobs — Binary data and BLOBs handling</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<a name="GdaBlobOp.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include &lt;libgda/gda-blob-op.h&gt;

                    <a class="link" href="GdaBlobOp.html#GdaBlobOp-struct" title="GdaBlobOp">GdaBlobOp</a>;
<a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               <a class="link" href="GdaBlobOp.html#gda-blob-op-get-length" title="gda_blob_op_get_length ()">gda_blob_op_get_length</a>              (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>);
<a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               <a class="link" href="GdaBlobOp.html#gda-blob-op-read" title="gda_blob_op_read ()">gda_blob_op_read</a>                    (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> size</code></em>);
<a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="GdaBlobOp.html#gda-blob-op-read-all" title="gda_blob_op_read_all ()">gda_blob_op_read_all</a>                (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);
<a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               <a class="link" href="GdaBlobOp.html#gda-blob-op-write" title="gda_blob_op_write ()">gda_blob_op_write</a>                   (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>);
<a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="GdaBlobOp.html#gda-blob-op-write-all" title="gda_blob_op_write_all ()">gda_blob_op_write_all</a>               (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);
</pre>
</div>
<div class="refsect1">
<a name="GdaBlobOp.object-hierarchy"></a><h2>Object Hierarchy</h2>
<pre class="synopsis">
  <a href="http://library.gnome.org/devel/gobject/unstable/gobject-The-Base-Object-Type.html#GObject">GObject</a>
   +----GdaBlobOp
</pre>
</div>
<div class="refsect1">
<a name="GdaBlobOp.description"></a><h2>Description</h2>
<p>
This object is a base class for individual database providers which support BLOB types. It supports
operations to read and write data in a BLOB value (of type GDA_BLOB_TYPE).
</p>
<p>
Libgda offers two methods to manipulate binary values as two containers: <a class="link" href="libgda-4.0-Gda-Value.html#GdaBinary">GdaBinary</a>
and <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob">GdaBlob</a>:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>When reading from a data model returned by <span class="application">Libgda</span> binary data will often be in a GdaBlob object, and the
      associated <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object can be used to manipulate the binary object (in a
      database for example)</p></li>
<li class="listitem"><p>When the binary value is created by the user, then there is no point in using a GdaBlob as
      there can not be any <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object, so the GdaBinary container is
      enough.</p></li>
</ul></div>
<p>
</p>
<p>
  Note that a <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob">GdaBlob</a> value (the "data" attribute) will often not contain any data
  (or only some part of the actual BLOB)
  and that it's up to the user to use the associated <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object to
  "load" the data into the container (into the actual process heap).
</p>
<p>
  For example to load the 1st 40 bytes of a blob:
  </p>
<pre class="programlisting">
GValue *blob_value = ...
GdaBlob *blob;
blob = (GdaBlob*) gda_value_get_blob (blob_value);
gda_blob_op_read (blob-&gt;op, blob, 0, 40);
  </pre>
<p>
</p>
<p>
  Another example is to write the contents of a blob to a file on disk, using a special
  <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object (internal to <span class="application">Libgda</span> which interfaces
  with a file in a filesystem):
  </p>
<pre class="programlisting">
GValue *blob_value; /* value to copy from */
GValue *tmp_value;
GdaBlob *file_blob;
GValue *blob_value = ...
tmp_value = gda_value_new_blob_from_file ("MyFile.bin");
file_blob = (GdaBlob*) gda_value_get_blob (tmp_value);
if (! gda_blob_op_write_all (file_blob-&gt;op, gda_value_get_blob (blob_value))) {
       /* error */
}
else {
       gsize size;
       size = gda_blob_op_get_length (file_blob-&gt;op);
       g_print ("Wrote %s, size = %d\n", filename, size);
}
gda_value_free (tmp_value);
  </pre>
<p>
</p>
<p>
  For further information, see:
  </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>the section about <a class="link" href="gen_blobs.html" title="Binary large objects (BLOBs)">Binary large objects (BLOBs)</a>'s
	abstraction</p></li>
<li class="listitem"><p><a class="link" href="libgda-provider-blobop.html" title="Virtual methods for Blob operations">Virtual methods for Blob operations</a>
	section for more information
	about how to implement the virtual methods when creating a database provider</p></li>
</ul></div>
<p>
</p>
</div>
<div class="refsect1">
<a name="GdaBlobOp.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="GdaBlobOp-struct"></a><h3>GdaBlobOp</h3>
<pre class="programlisting">typedef struct _GdaBlobOp GdaBlobOp;</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-get-length"></a><h3>gda_blob_op_get_length ()</h3>
<pre class="programlisting"><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               gda_blob_op_get_length              (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>);</pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>op</code></em> :</span></p></td>
<td>an existing <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the length of the blob in bytes. In case of error, -1 is returned and the
provider should have added an error (a <a class="link" href="GdaConnectionEvent.html" title="GdaConnectionEvent"><span class="type">GdaConnectionEvent</span></a>) to the connection.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-read"></a><h3>gda_blob_op_read ()</h3>
<pre class="programlisting"><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               gda_blob_op_read                    (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> size</code></em>);</pre>
<p>
Reads a chunk of bytes from the BLOB accessible through <em class="parameter"><code>op</code></em> into <em class="parameter"><code>blob</code></em>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>op</code></em> :</span></p></td>
<td>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>blob</code></em> :</span></p></td>
<td>a <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> to read data to</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>offset</code></em> :</span></p></td>
<td>offset to read from the start of the blob (starts at 0)</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>size</code></em> :</span></p></td>
<td>maximum number of bytes to read.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the number of bytes actually read. In case of error, -1 is returned and the
provider should have added an error to the connection.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-read-all"></a><h3>gda_blob_op_read_all ()</h3>
<pre class="programlisting"><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gda_blob_op_read_all                (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);</pre>
<p>
Reads the whole contents of the blob manipulated by <em class="parameter"><code>op</code></em> into <em class="parameter"><code>blob</code></em>
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>op</code></em> :</span></p></td>
<td>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>blob</code></em> :</span></p></td>
<td>a <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> to read data to</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>TRUE if <em class="parameter"><code>blob-&gt;data</code></em> contains the whole BLOB manipulated by <em class="parameter"><code>op</code></em>
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-write"></a><h3>gda_blob_op_write ()</h3>
<pre class="programlisting"><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>               gda_blob_op_write                   (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                                                         <em class="parameter"><code><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>);</pre>
<p>
Writes a chunk of bytes from a <em class="parameter"><code>blob</code></em> to the BLOB accessible through <em class="parameter"><code>op</code></em>, <em class="parameter"><code>blob</code></em> is unchanged after
this call.
</p>
<p>
If <em class="parameter"><code>blob</code></em> has an associated <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> (ie. if <em class="parameter"><code>blob-&gt;op</code></em> is not <a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>) then the data to be written
using <em class="parameter"><code>op</code></em> is the data fetched using <em class="parameter"><code>blob-&gt;op</code></em>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>op</code></em> :</span></p></td>
<td>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>blob</code></em> :</span></p></td>
<td>a <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> which contains the data to write</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>offset</code></em> :</span></p></td>
<td>offset to write from the start of the blob (starts at 0)</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the number of bytes written. In case of error, -1 is returned and the
provider should have added an error to the connection.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-write-all"></a><h3>gda_blob_op_write_all ()</h3>
<pre class="programlisting"><a href="http://library.gnome.org/devel/glib/unstable/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gda_blob_op_write_all               (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                                                         <em class="parameter"><code><a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);</pre>
<p>
Writes the whole contents of <em class="parameter"><code>blob</code></em> into the blob manipulated by <em class="parameter"><code>op</code></em>. If necessary the resulting
blob is truncated from its previous length.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>op</code></em> :</span></p></td>
<td>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>blob</code></em> :</span></p></td>
<td>a <a class="link" href="libgda-4.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> which contains the data to write</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>TRUE on success</td>
</tr>
</tbody>
</table></div>
</div>
</div>
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