how to select from key which field not empty

StackOverflow https://stackoverflow.com/questions/12337130

  •  01-07-2021
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Question

i have xml file and xslt transformation below:

    <?xml version="1.0" encoding="utf-8" ?>
    <?xml-stylesheet version="1.0" type="text/xml" href="pets.xsl" ?>
    <pets>
        <pet name="Jace" type="dog" />
        <pet name="Babson" type="" />
        <pet name="Oakley" type="cat" />
        <pet name="Tabby" type="dog" />
    </pets>

<?xml version="1.0" encoding="utf-8" ?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
    <xsl:key name="pets-key" match="pet" use="type" />
    <xsl:template match="/" >
        <html>
            <head><title></title></head>
            <body>
                <xsl:for-each select="key('pets-key', '' )" >
                    <xsl:value-of select="@name" />
                </xsl:for-each>
            </body>
        </html>
    </xsl:template>
</xsl:stylesheet>

How can i select all pets which types not empty using key function?

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Solution

Two points to note:

  1. There is an error in your key definition. You need to use use="@type", not use="type"

  2. You need a set difference to select all pets whose type is non-empty, and still use the key() function. The general recipe for set difference in XPATH 1.0 is...

    $node-set1[count(. | $node-set2) != count($node-set2)]

Putting it altogether, a correct but inefficent XSLT 1.0 style-sheet to use the key() and list all pets with not empty type is...

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
<xsl:output method="html" indent="yes" />
<xsl:strip-space elements="*" />

<xsl:key name="kPets" match="pet" use="@type" />

<xsl:template match="/" >
  <html>
    <head><title>Pets with a type</title></head>
    <body>   
      <ul>
        <xsl:for-each select="*/pet[count(. | key('kPets', '' )) != count(key('kPets', '' ))]" >
          <li><xsl:value-of select="@name" /></li>
        </xsl:for-each>
      </ul>
    </body>
   </html>
</xsl:template>

</xsl:stylesheet>

This yields output...

<html>
  <head>
    <META http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>Pets with a type</title>
  </head>
  <body>
    <ul>
      <li>Jace</li>
      <li>Oakley</li>
      <li>Tabby</li>
    </ul>
  </body>
</html>

Having said that, the question does not really fit as a good excersize in using keys. In real life, if you wanted to achieve this outcome, a better, more efficient XSLT 1.0 solution would be ...

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
<xsl:output method="html" indent="yes" />
<xsl:strip-space elements="*" />

<xsl:key name="kPets" match="pet" use="@type" />

<xsl:template match="/*" >
  <html>
    <head><title>Pets with a type</title></head>
    <body>   
      <ul>
        <xsl:apply-templates />
      </ul>
    </body>
   </html>
</xsl:template>

<xsl:template match="pet[@type != .]">
  <li><xsl:value-of select="@name" /></li>
</xsl:template>  

</xsl:stylesheet>
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