Hi, all

I want to implement sorting of the following piece of xml.
Sorting key should be, depending on previously defined variable:
- policy/@name or
- policy/description or
- policy/@created or even
- rule[@id = policy/rule/@id]/@name (I didn't tested this expression for correctness, it's just to explain the idea)

So I need an expression that selects correct expression depending on variable/param value.
I tried this:

<xsl:param name="sorted-by-column" >1</xsl:param>
<xsl:variable name="sorting-expression">
  <xsl:choose>
    <xsl:when test="$sorted-by-column = 1">
      <xsl:value-of select="@name"/>
    </xsl:when>
    <xsl:when test="$sorted-by-column = 2">
      <xsl:value-of select="./description"/>
    </xsl:when>
    ...
  </xsl:choose>
</xsl:variable>
...
<xsl:for-each select="policy">
  <xsl:sort select="$sorting-expression" order="{$sorting-order}"/>
</xsl:for-each>

...and this:
<xsl:sort select="{$sorting-expression}" order="{$sorting-order}"/>

It gives me errors from 'Invalid XPath expression' to 'Node cannot be an expression'.


XML:
<rule id="22" name="Name1"/>
<rule id="19" name="Name2"/>
...
<policy id="1" name="AA" created="1133388000" modified="1141920863">
  <description>BBB</description>
    <rule1 id="19"/>
    <rule2 id="22"/>
    <rule3 id="25"/>
</policy>
<policy id="2" name="BB" created="1133388000" modified="1141920863">
...
</policy>

In XSLT 2.0 you can do

xsl:sort select="if ... then policy/@name
                 else if ... then policy/description
                 else ...

It's not so easy in 1.0. Some of the entries in Dave Pawson's FAQ relate to this problem:

http://www.dpawson.co.uk/xsl/sect2/N6461.html#d8741e455

If you've got a processor that offers xx:evaluate() (e.g. Saxon) then you can put the XPath expression into a string variable $sort-key and do xsl:sort select="saxon:evaluate($sort-key)".

Another technique is

<xsl:sort select="policy/@name[$condition=1]"/>
<xsl:sort select="policy/description[$condition=2]"/>
<xsl:sort select="policy/@created[$condition=3]"/>



Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Thanks, Michael! This is of greate help.