xslt - xsl:variable as xpath value for other xsl tag

Question

I'm having issues with xsl:variable. I want to create a variable with a value that depends on the value of another XML node attribute. This working good. But when I try to create a variable with a string value that represents XPath, it just doesn't work when I try to use it as XPath in a later XSL tag.

<xsl:variable name="test">  
  <xsl:choose>
    <xsl:when test="node/@attribute=0">string/represent/xpath/1</xsl:when>
    <xsl:otherwise>string/represent/xpath/2</xsl:otherwise>
  </xsl:choose>       
</xsl:variable>                 
<xsl:for-each select="$test">
  [...]
</xsl:for-each>

I tried: How to use xsl variable in xsl if and trouble with xsl:for-each selection using xsl:variable. But with no results.

Answer 1

Dynamic evaluation of an XPath expression is generally not supported in XSLT (both 1.0 and 2.0), however:

We can implement a rather general dynamic XPath evaluator if we only restrict each location path to be an element name:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output method="text"/>

 <xsl:param name="inputId" select="'param/yyy/value'"/>

 <xsl:variable name="vXpathExpression"
  select="concat('root/meta/url_params/', $inputId)"/>

 <xsl:template match="/">
  <xsl:value-of select="$vXpathExpression"/>: <xsl:text/>

  <xsl:call-template name="getNodeValue">
    <xsl:with-param name="pExpression"
         select="$vXpathExpression"/>
  </xsl:call-template>
 </xsl:template>

 <xsl:template name="getNodeValue">
   <xsl:param name="pExpression"/>
   <xsl:param name="pCurrentNode" select="."/>

   <xsl:choose>
    <xsl:when test="not(contains($pExpression, '/'))">
      <xsl:value-of select="$pCurrentNode/*[name()=$pExpression]"/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:call-template name="getNodeValue">
        <xsl:with-param name="pExpression"
          select="substring-after($pExpression, '/')"/>
        <xsl:with-param name="pCurrentNode" select=
        "$pCurrentNode/*[name()=substring-before($pExpression, '/')]"/>
      </xsl:call-template>
    </xsl:otherwise>
   </xsl:choose>
 </xsl:template>
</xsl:stylesheet>

when this transformation is applied on this XML document:

<root>
  <meta>
    <url_params>
      <param>
        <xxx>
          <value>5</value>
        </xxx>
      </param>
      <param>
        <yyy>
          <value>8</value>
        </yyy>
      </param>
    </url_params>
  </meta>
</root>

the wanted, correct result is produced:

root/meta/url_params/param/yyy/value: 8