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<h1>22. Virtuoso Functions Guide - xpf_extension</h1>
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<div id="text">
<h2>xpf_extension</h2>
<div class="refpurpose">declare an XPath extension function </div>
<div class="funcsynopsis">
<span class="funcdef">void <span class="function">xpf_extension</span>
</span>
(<span class="paramdef">in <span class="parameter">fname</span> varchar</span>,
<span class="paramdef">in <span class="parameter">procedure_name</span> varchar</span>);
</div>
<div class="refsect1">
<div class="refsect1title">Description</div>
<p>
This function is used to declare a new XPath extension function or
redefine an existing function. It can be used in XPath queries and
XSLT stylesheets. You should use QNames for extension functions.
Note that the standard XPath functions cannot be redefined.</p>
<p>
<span class="computeroutput">xpf_extension()</span> stores the functions into
the SYS_XPF_EXTENSIONS system table.
</p>
<div>
<pre class="programlisting">
CREATE TABLE
DB.DBA.SYS_XPF_EXTENSIONS (
XPE_NAME VARCHAR PRIMARY KEY,
XPE_PNAME VARCHAR
)
</pre>
</div>
<p>
The input parameters will be retrieved as a strings and then will be converted to the datatype of
the corresponding argument of the stored procedure.
</p>
</div>
<div class="refsect1">
<div class="refsect1title">Parameters</div>
<div class="refsect2">
<span class="refsect2title">fname – </span>
The name of the extension function, which must be the expanded QName
of the extension function</div>
<div class="refsect2">
<span class="refsect2title">procedure_name – </span>
The fully qualified name of the PL procedure which acts as
the extension function. The procedure in question must be granted to PUBLIC,
otherwise it will not be registered and error will be signalled.
</div>
</div>
<div class="refsect1">
<div class="refsect1title">Return Types</div>
<p>None (void).</p>
</div>
<div class="refsect1title">Errors</div>
<table class="data">
<tr>
<th class="data">SQLState</th>
<th class="data">Error Code</th>
<th class="data">Error Text</th>
<th class="data">Description</th>
</tr>
<tr>
<td class="data">
<a name="err42001" />
<span class="errorcode">42001</span>
</td>
<td class="data">
<a name="errXPE01" />
<span class="errorcode">XPE01</span>
</td>
<td class="data">
<span class="errorname">The function <procedure_name> does not exists</span>
</td>
<td class="data">if procedure to define as a XPATH extension function is not existing one.</td>
</tr>
<tr>
<td class="data">
<a name="err42001" />
<span class="errorcode">42001</span>
</td>
<td class="data">
<a name="errXPE02" />
<span class="errorcode">XPE02</span>
</td>
<td class="data">
<span class="errorname">The <built-in XPATH|XQUERY> function "<func name>" cannot be re-defined</span>
</td>
<td class="data">if XPATH or XQUERY function to be registered is a core function.</td>
</tr>
</table>
<br />
<p />
<div class="refsect1">
<div class="refsect1title">Examples</div>
<a name="ex_xpf_extension" />
<div class="example">
<div class="exampletitle">Declaring a New XSLT Function</div>
<p>First define a PL procedure, then declare an XPath extension
function and to represent it.</p>
<div>
<pre class="programlisting">
SQL> create procedure DB.DBA.str_concat (in a varchar, in b varchar)
{
return concat (a, ':', b);
};
SQL> xpf_extension ('http://www.openlinksw.com/virtuoso/xslt:concat_strings', 'DB.DBA.str_concat');
</pre>
</div>
<p> The source of the ([http_root]/ext.xsl) XSLT stylesheet </p>
<div>
<pre class="programlisting">
<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"
xmlns:virt="http://www.openlinksw.com/virtuoso/xslt">
<xsl:template match="/doc">
<HTML>
<BODY>
<xsl:if test="function-available('virt:concat_strings')">
<xsl:value-of select="virt:concat_strings ('foo', 'bar')"/>
</xsl:if>
</BODY>
</HTML>
</xsl:template>
</xsl:stylesheet>
</pre>
</div>
<p>The source of the
<span class="computeroutput">([http_root]/ext.vsp)</span> VSP page:
</p>
<div>
<pre class="programlisting">
<?vsp
http_xslt ('file:/ext.xsl');
?>
<doc>
<a/>
</doc>
</pre>
</div>
<p>
This will produce the following HTML page:
</p>
<div>
<pre class="programlisting">
<HTML><BODY>foo:bar</BODY></HTML>
</pre>
</div>
<p>Using the definition of the XPath extension function, we can
include it in XPath expressions.</p>
<div>
<pre class="programlisting">
SQL> select p from ws..sys_dav_res
where xpath_contains (RES_CONTENT,
'[xmlns:virt=''http://www.openlinksw.com/virtuoso/xslt'']
virt:concat_strings (''Title '', string(/chapter/title))', p);
</pre>
</div>
<p>This will return the contents of any '/chapter/title' nodes, prefixed
with constant string 'Title'.</p>
</div>
</div>
<div class="refsect1">
<div class="refsect1title">See Also</div>
<p>
<a href="fn_xpf_extension_remove.html">xpf_extension_remove</a>
</p>
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