Name

xpf_extension — declare an XPath extension function

Synopsis

void xpf_extension ( in fname varchar ,
  in procedure_name varchar );
 

Description

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.

xpf_extension() stores the functions into the SYS_XPF_EXTENSIONS system table.

      CREATE TABLE
        DB.DBA.SYS_XPF_EXTENSIONS (
            XPE_NAME VARCHAR PRIMARY KEY,
            XPE_PNAME VARCHAR
            )
    

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.

Parameters

fname

The name of the extension function, which must be the expanded QName of the extension function

procedure_name

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.

Return Types

None (void).

Errors

Table 24.136. Errors signalled by

SQLState Error Code Error Text Description
42001 XPE01 The function <procedure_name> does not exists if procedure to define as a XPATH extension function is not existing one.
42001 XPE02 The <built-in XPATH|XQUERY> function " <func name>" cannot be re-defined if XPATH or XQUERY function to be registered is a core function.

Examples

Example 24.531. Declaring a New XSLT Function

First define a PL procedure, then declare an XPath extension function and to represent it.

SQL> create procedure DB.DBA.str_concat (in a varchar, in b varchar)
     {
       return concat (a, ':', b);
     };

SQL> xpf_extension ('http://example.com/virtuoso/xslt:concat_strings', 'DB.DBA.str_concat');

The source of the ([http_root]/ext.xsl) XSLT stylesheet

<?xml version='1.0'?>

<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/TR/WD-xsl"
  xmlns:virt="http://example.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>

The source of the

([http_root]/ext.vsp)

VSP page:

<?vsp
  http_xslt ('file:/ext.xsl');
?>
<doc>
<a/>
</doc>

This will produce the following HTML page:

<HTML><BODY>foo:bar</BODY></HTML>

Using the definition of the XPath extension function, we can include it in XPath expressions.

SQL> select p from ws..sys_dav_res
where xpath_contains (RES_CONTENT,
'[xmlns:virt=''http://example.com/virtuoso/xslt'']
virt:concat_strings (''Title '', string(/chapter/title))', p);

This will return the contents of any '/chapter/title' nodes, prefixed with constant string 'Title'.