Question

My XML Code (containing pubs and people):

<document>
    <pubs>
        <pub id="pub1">
            <open>true</open>
        </pub>
        <pub id="pub2">
            <open>false</open>
        </pub>
    </pubs>
    <people>
        <person>
            <name>John</name>
            <pubId>pub1</pubId>
        </person>
        <person>
            <name>Paul</name>
            <pubId>pub2</pubId>
        </person>
    </people>
</document>

uses a reference from <person> to <pub> (person/pubId references pub[@id]). Pubs themselves have a boolean <open> (stating whether the pub is opened or closed).

Using XSLT, I want to be able to count() the number of people that can go to the pub. In order to go to a pub, the pub must have an <open> value of true.

Two possible solutions that I can’t quite code up:

1. Iterate through the people and keep track of the number:

   <xsl:for-each select="person">
       <xsl:variable name="pId" select="pubId" />
   
       <xsl:if test="root()/document/pubs/pub[@pubId=$pId]/open = 'true'" >
           <!-- any way to keep track of this number? -->
       </xsl:if>
   </xsl:for-each>
   

2. Use the count() function directly:

   <count>
       <xsl:value-of select="count(//person[root()/document/pubs/pub[@id = pubId]/open = 'true'])" />
   </count>
   

The second option seems more concise and correct, but I can’t get it to work.

Any ideas?

Answer 1

Use this XPath 1.0 one-liner:

count(/*/people/person[pubId = /*/pubs/pub[open = 'true']/@id])

This returns the count of person elements in this document that have at least one pubId child such that there is a pub element whose id attribute’s string value equals that pubId and whose open child’s string value is the string "true".

Here is an XSLT-based verification:

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

 <xsl:template match="/">
  <xsl:copy-of select=
      "count(/*/people/person[pubId = /*/pubs/pub[open = 'true']/@id])"/>
 </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the provided XML document:

<document>
    <pubs>
        <pub id="pub1">
            <open>true</open>
        </pub>
        <pub id="pub2">
            <open>false</open>
        </pub>
    </pubs>
    <people>
        <person>
            <name>John</name>
            <pubId>pub1</pubId>
        </person>
        <person>
            <name>Paul</name>
            <pubId>pub2</pubId>
        </person>
    </people>
</document>

the Xpath expression is evaluated and the result of this evaluation is copied to the output:

1