XSLT Joins

chiefos · June 9th, 2008, 05:41 AM

Hi All,

I am VERY new to XSLT and I have hit a stumbling block. I have an xml file in the following format (simplified):

Code:

<listing>
  <venueList>
    <venue venueID="x100clu">

    </venue>
  </venueList>
  <titleList>
    <title titleID="ybrakes" titleName="Brakes">
      <category categoryName="mus" subCategory="rock"></category>

    </title>
   </titleList>
  <eventList>
    <event eventID="z4331565" titleID="ybrakes" venueID="x100clu" />
  <eventList>
</listing>

What I basically want to achieve is a transformed XML file that shows a list of venues that will with a 'description' node. These venues will not be distinct but a venue will be unique for each category i.e.

Code:

<venues>
  <venue id="venue1">
    <category>Cat1</category>
    <description>
     <!-- 
     all "titleList/title[@titleName] for events that are in this 
     venue AND this category 
     -->
    </description>
  </venue>
  <venue id="venue1">
    <category>Cat2</category>
    <description>
     <!-- 
     all "titleList/title[@titleName] for events that are in this 
     venue AND this category 
     -->
    </description>
  </venue>
  <venue id="venue2">
    <category>Cat2</category>
    <description>
     <!-- 
     all "titleList/title[@titleName] for events that are in this 
     venue AND this category 
     -->
    </description>
  </venue>
</venues>

Where do I begin?

mhkay · June 9th, 2008, 06:07 AM

I think this is a combination of joining and grouping. You basically want something like

<xsl:for-each select="listing/venueList/venue">
  <xsl:variable name="events" select="listing/eventList/event[@venueId=current()/@venueId]"/>
  <xsl:variable name="titles" select="/listing/titleList/title[@titleId=$events/@titleId"/>
<xsl:for-each-group select="$titles" group-by="category/categoryName">
  <venue id="@venueId">
    <category><xsl:value-of select="current-grouping-key()"/></category>
      <xsl:apply-templates select="current-group()"/>
    </category>
  </venue>

xsl:for-each-group is XSLT 2.0; if you have to use 1.0 the syntax is much clumsier, search for "Muenchian grouping".

Note also that the join can be speeded up using xsl:key if your data volumes are large.

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

chiefos · June 9th, 2008, 08:49 AM

I get that for-each-group cannot be a child of for-each?

Martin Honnen · June 9th, 2008, 08:53 AM

xsl:for-each-group is XSLT 2.0, if you get an error message using that instruction then it is likely because you use an XSLT 1.0 processor.
Saxon, Gestalt, and AltovaXML are the only XSLT 2.0 processors so far.

--
Martin Honnen
Microsoft MVP - XML

mhkay · June 9th, 2008, 10:34 AM

>I get that for-each-group cannot be a child of for-each?

That probably means you're using an XSLT 1.0 processor. As Martin said, there are a lot of them still around.

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