How to evaluate parameter?

chobo · February 24th, 2008, 06:00 AM

Hi, I'm trying to use a passed parameter in the xsl:sort tag, but from what I have researched it treats it as a string when it should be evaluated as an xslt expression. How can I get the following to work? Thanks!

Code:

  <xsl:param name="order" />
  <xsl:param name="dataType" />
  <xsl:param name="sortExpression" />

  <xsl:template match="/">    
      <xsl:for-each select="//aws:Item">
        <xsl:sort select="$sortExpression" data-type="{$dataType}" order="{$order}" />
        <xsl:value-of select="$sortExpression" />

joefawcett · February 24th, 2008, 06:06 AM

You can't do this directly. Dynamic evaluation of XPath is not supported in XSLT. You might be able to modify the path or use other techniques but you need to show a sample of the XML and XSLT.

--

Joe (Microsoft MVP - XML)

mhkay · February 24th, 2008, 07:15 AM

If the string is just an element name you can use

select="*[name()=$param]"

Otherwise you will have to use an extension such as saxon:evaluate().

Another approach (which I use sometimes when running transformations in the browser) is to modify the stylesheet before compiling it, to include the text of the expression.

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

chobo · February 24th, 2008, 04:21 PM

The only reason I need to pass a select expression is to test whether or not to sort the content. The xsl:sort command is quite picky and from what I know, you can't use conditionals with it. Would you guys have any suggestions for choosing between two different sorting scenarios?

chobo · February 24th, 2008, 05:30 PM

I figured out a way to do a conditional sort :) For my case there were two different sort scenarios, one where I didn't want to sort and one where I did. What I did was create and pass a dummy parameter to the style sheet from my c# file, much like I did with my other parameters. In the xsl:sort statement I added a condition to the end of the select portion.

Here is some code snippets

Code:

<xsl:sort select="aws:OfferSummary/aws:LowestNewPrice/aws:Amount[number($dummyValue) >= 0]" data-type="{$dataType}" order="{$order}" />

If I want to sort, I set the $dummyValue to 0 in my c# code and pass it to the stylesheet, if I don't want to sort I pass -1. I also pass parameters for the datatype and order. Those parameters don't need any special attention like the select value one, so just pass and use those like I did above.

Hope this helps anyone out there trying to do conditional sorting!

samjudson · February 25th, 2008, 05:30 AM

Is my memory playing tricks on me or does the following not work:

Code:

<xsl:for-each ...>
  <xsl:if test="$dummy = 0">
    <xsl:sort select="..."/>
  </xsl:if>
  ...
</xsl:for-each>

/- Sam Judson : Wrox Technical Editor -/

joefawcett · February 25th, 2008, 06:11 AM

I think xsl:sort has to have apply-templates/for-each as an immediate parent.

--

Joe (Microsoft MVP - XML)

samjudson · February 25th, 2008, 06:32 AM

Yeah you're right, my mind was playing tricks on me.

Another option would be to take the contents of the xsl:for-each and put it in a template, then have two for-each statements inside a xsl:choose/xsl:when, one with a sort, the other without.

Or just use the method you've got above.

/- Sam Judson : Wrox Technical Editor -/

mhkay · February 25th, 2008, 07:05 AM

Personally, rather than incurring the potential expense of doing a sort in which all the sort keys are equal, I would do

<xsl:choose>
  <xsl:when test="$dummy = 0">
     <xsl:for-each select="xxx">
        <xsl:sort .../>
        <xsl:call-template name="body"/>
     </xsl:for-each>
  </xsl:when>
  <xsl:otherwise>
     <xsl:for-each select="xxx">

        <xsl:call-template name="body"/>
     </xsl:for-each>
  </xsl:otherwise>
</xsl:choose>

(or better, an equivalent using xsl:apply-templates)

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