Question

I have an input XML file which I need to copy 1:1 to the output, except for one subelement which contains subitems that need to be sorted.

<?xml version='1.0'?> <top>   <elementA />   <elementB />   <contents>       <contentitem>           <id>3</id>           <moretags1 />           <moretags2 />       </contentitem>       <contentitem>           <id>2</id>           <moretags1 />           <moretags2 />       </contentitem>       <contentitem>           <id>1</id>           <moretags1 />           <moretags2 />       </contentitem>   </contents> </top> 

I’d like an XSL Transformation that puts the ‘contentitem’ elements in order, sorted by their ‘id’ elements. All other tags, including nested ones, must be copied verbatim. I already tried with xsl:copy, but either I get double contents or something turns out missing.

Answer 1

Mark Gravell’s solution is almost correct — with a slight issue that creates two nested <contents> elements. Note to all who provide answers: Do test your solutions!

Here is a correct solution. This transformation:

<xsl:stylesheet version='1.0'   xmlns:xsl='http://www.w3.org/1999/XSL/Transform'>  <xsl:output omit-xml-declaration='yes' indent='yes'/> <!--                                                -->   <xsl:strip-space elements='*'/> <!--                                                -->    <xsl:template match='node()|@*'>     <xsl:copy>       <xsl:apply-templates select='node()|@*'/>     </xsl:copy>   </xsl:template> <!--                                                -->    <xsl:template match='contents'>     <xsl:copy>       <xsl:apply-templates select='@*'/>       <xsl:apply-templates select='contentitem'>         <xsl:sort select='id' data-type='number'/>       </xsl:apply-templates>     </xsl:copy>   </xsl:template> </xsl:stylesheet> 

when applied on the originally-provided XML document:

<top>     <elementA />     <elementB />     <contents>         <contentitem>             <id>3</id>             <moretags1 />             <moretags2 />         </contentitem>         <contentitem>             <id>2</id>             <moretags1 />             <moretags2 />         </contentitem>         <contentitem>             <id>1</id>             <moretags1 />             <moretags2 />         </contentitem>     </contents> </top> 

produces the wanted, correct result:

<top>    <elementA/>    <elementB/>    <contents>       <contentitem>          <id>1</id>          <moretags1/>          <moretags2/>       </contentitem>       <contentitem>          <id>2</id>          <moretags1/>          <moretags2/>       </contentitem>       <contentitem>          <id>3</id>          <moretags1/>          <moretags2/>       </contentitem>    </contents> </top> 

Do note the following:

1. The use of the identity rule to copy all nodes without change.

2. How the identity template is overriden with a specific template matching the contents element

3. The use of the <xsl:sort> instruction to present the results of applying a template in a specific order, possibly different from the document order of the nodes, selected for processing.