Global variable restrictions in the <xsl:key>

iceandrews · August 25th, 2008, 10:30 AM

I'm trying to use a Global variable in the <xsl:key> instruction. I read that in 2.0 the restrictions on this have been relaxed, but I can't seem to find any documentation on the rules. Obviously, I cannot make use of variants of <xsl:key name="KeyRef" match="$MappingFile/MessageMapping/List" use="@Src"/>

Below is what I'm trying to accomplish.

It should be noted that the "LUT.xsl" contains the global variable $MappingFile and the 'MappingFile.xml' is just a document with the $MappingFile variable as an XML document. But this gives a short example of what I mean.

I will probably have multiple lookup tables coming from multiple external documents. Is there a more elegant way to execute this using 2.0 now that the restrictions have been relaxed?

Code:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:include href="LUT.xsl"/>
    <xsl:variable name="LookupTable" select="document('MappingFile.xml')"/>

    <xsl:key name="KeyRef" match="MessageMapping/List" use="@Src"/>
    <xsl:key name="KeyRefItem" match="MessageMapping/List/Enum" use="@Src"/>

    <xsl:template match="/">
        <xsl:variable name="sKey" select="'Dummy_Enum'"/>
        <xsl:variable name="sList" select="'Dummy_List'"/>


        <Direct>
            <xsl:value-of select="$MappingFile/MessageMapping/List[@Src = $sList]/@Tgt"/>
            <xsl:copy-of select="$MappingFile/MessageMapping/List[@Src = $sList]/Enum[@Src = $sKey]"/>
        </Direct>


        <xsl:for-each select="$LookupTable">
            <Document>
                <xsl:value-of select="key('KeyRefItem',$sKey)[../@Src = $sList]/../@Tgt"/>
                <xsl:copy-of select="key('KeyRefItem',$sKey)"/>
            </Document>
        </xsl:for-each>
    </xsl:template>
</xsL:stylesheet>

mhkay · August 25th, 2008, 12:21 PM

You don't need the global variable here. Just define the xsl:key with match="MessageMapping/List". The document that is searched is defined by the context node at the time you call the key() expression, not by the xsl:key definition, and a typical implementation will only build an index for a document the first time you call key() to search that document.

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

iceandrews · August 25th, 2008, 01:16 PM

I see, that provides a little bit of clarity.

I did notice that I can simply put this and it still works properly. Thus eliminating the document() form the XSLT, since the variable is already in the included LUT.xsl

Code:

<xsl:for-each select="$MappingFile">
     <Document>
         <xsl:value-of select="key('KeyRefItem',$sKey)[../@Src = $sList]/../@Tgt"/>
         <xsl:copy-of select="key('KeyRefItem',$sKey)"/>
     </Document>
</xsl:for-each>

So I've been reading the changes of <xsl:key> between 1.0 and 2.0, but I still can't extract the eased restrictions on global variables in the 'match' and 'use' attributes.

In 1.0, using <xsl:for-each> was the only way to "change" the context node so the key() function could reference a LookupTable from an external source (document, included xslt, etc). So there is no way to "pre-build" various indexes, so a single key could be used to match against all of them. The <xsl:for-each> seems like a very "trick" method. It also is restricting the key to the single document tree/context node, rather then the pool of all possible global available trees. (Multiple included xsls, with mulitple LUTs)