XSLT xsl:for-each conditional selection

Question

I have a piece of xml that looks like this:

<root>
  <tag1>tractor</tag1>
  <tag2>
    <subtag1 att="apple" />
    <subtag2>
      <subsubtag1>red</subsubtag1>        
      <subsubtag2>lunch</subsubtag2>
    </subtag2>
  </tag2>      
  <tag1>forklift</tag1>
  <tag2>
    <subtag1 att="pear" />
    <subtag2>
      <subsubtag1>green</subsubtag1>        
      <subsubtag2>breakfast</subsubtag2>
    </subtag2>
  </tag2>      
  <tag2>
    <subtag1 att="apple" />
    <subtag2>
      <subsubtag1>green</subsubtag1>        
      <subsubtag2>dinner</subsubtag2>
    </subtag2>
  </tag2>   
  <tag1>combine harvester</tag1>
</root>

What I need to get transform it so that I get subtags 2 and 3 from each tag2 node, but only the tag2 nodes where subtag1 is apple. I also need a sequence number for each.

My current code looks something like this:

<xsl:for-each select="//tag2">
  <apple>
    <seq_num><xsl:value-of select="position()" /></seq_num>
    <colour><xsl:value_of select="subtag2" /></colour>  
    <meal><xsl:value_of select="subtag3" /></meal>  
  </apple>
</xsl:for-each>

This would be fine, except that I need the for-each only to return the tag2 which are apples (i.e. subtag1 = apple). I can't use an xsl:if or an xsl:when because then the sequence number would be inaccurate for the second apple.

Any ideas?

Thanks, Rik

Answer 1

To stay with your code, should be as simple as:

<xsl:for-each select="//tag2[subtag1/@att='apple']">
  <apple>
    <seq_num><xsl:value-of select="position()" /></seq_num>
    <colour><xsl:value-of select="subtag2/subsubtag1" /></colour>  
    <meal><xsl:value-of select="subtag2/subsubtag2" /></meal>  
  </apple>
</xsl:for-each>

As per the comments below, as suggested, it's better avoid //. You should be able when in the correct context. For instance:

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

    <xsl:output method="xml" indent="yes"/>
    <xsl:strip-space elements="*"/>

    <xsl:template match="/root">
        <xsl:for-each select="tag2[subtag1/@att='apple']">
            <apple>
                <seq_num><xsl:value-of select="position()" /></seq_num>
                <colour><xsl:value-of select="subtag2/subsubtag1" /></colour>  
                <meal><xsl:value-of select="subtag2/subsubtag2" /></meal>  
            </apple>
        </xsl:for-each>
    </xsl:template>

</xsl:stylesheet>

Apllied on your input, produces the same result. Or still better, avoid the xsl:for-each as well:

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

    <xsl:output method="xml" indent="yes"/>
    <xsl:strip-space elements="*"/>

    <xsl:template match="/root">
        <xsl:apply-templates select="tag2[subtag1/@att='apple']"/>
    </xsl:template>

    <xsl:template match="tag2">
        <apple>
            <seq_num><xsl:value-of select="position()" /></seq_num>
            <colour><xsl:value-of select="subtag2/subsubtag1" /></colour>  
            <meal><xsl:value-of select="subtag2/subsubtag2" /></meal>  
        </apple>
    </xsl:template>

</xsl:stylesheet>