XSLT 1.0 sort elements

Question

I have the following XML document:

<?xml version="1.0" encoding="UTF-8"?>
<objects>
    <object>Clutch</object>
    <object>Gearbox</object>
    <object>Cylinder head</object>
    <object>Starter</object>
    <object>Airbox</object>
    <object>Inlet manifold</object>
</objects>

And the following XSLT document:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="xml" indent="yes"/>

    <xsl:template match="objects">
        <parts>
            <xsl:apply-templates>
                <xsl:sort select="object"/>
            </xsl:apply-templates>
        </parts>
    </xsl:template>

    <xsl:template match="object">
        <part>
            <xsl:apply-templates/>
        </part>
    </xsl:template>

</xsl:stylesheet>

When applied I am getting the following output as expected, but it is not being sorted:

<?xml version="1.0" encoding="UTF-8"?>
<parts>
    <part>Clutch</part>
    <part>Gearbox</part>
    <part>Cylinder head</part>
    <part>Starter</part>
    <part>Airbox</part>
    <part>Inlet manifold</part>
</parts>

Why is the <xsl:sort select="object"/> not being applied ?

Answer 1

The reason is here:

  <parts> <xsl:apply-templates> <xsl:sort select="object"/> </xsl:apply-templates> </parts> 

This applies templates to the children ( object ) of the current node ( objects ) and sorts them by the string value of their first object child.

However in the provided XML document an object doesn't have any object children -- so they all have the same sort-key -- the empty string -- and their original order isn't changed by the sort operation.

Solution :

        <parts>
            <xsl:apply-templates>
                <xsl:sort select="."/>
            </xsl:apply-templates>
        </parts>

The complete transformation becomes :

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

 <xsl:template match="objects">
    <parts>
     <xsl:apply-templates>
        <xsl:sort select="."/>
     </xsl:apply-templates>
    </parts>
 </xsl:template>

 <xsl:template match="object">
  <part>
     <xsl:apply-templates/>
  </part>
 </xsl:template>
</xsl:stylesheet>

and when it is applied to the provided XML document:

<objects>
    <object>Clutch</object>
    <object>Gearbox</object>
    <object>Cylinder head</object>
    <object>Starter</object>
    <object>Airbox</object>
    <object>Inlet manifold</object>
</objects>

the wanted, correct result is produced:

<parts>
   <part>Airbox</part>
   <part>Clutch</part>
   <part>Cylinder head</part>
   <part>Gearbox</part>
   <part>Inlet manifold</part>
   <part>Starter</part>
</parts>