Question

Given this XML

<Xml>
    <Thing id="1"  >
        <Foo id="11" parentId="12"/>
        <Foo id="12"/>
    </Thing>
    <Thing id="2" parentId="1" />
    <Thing id="3" parentId="2" />
    <Thing id="4">
        <Foo id="11" parentId="15"/>
        <Foo id="12" parentId="14"/>
        <Foo id="13" parentId="11"/>
        <Foo id="14" parentId="15"/>
        <Foo id="15"/>      
    </Thing>
</Xml>

I want to grab every collection of siblings, and assemble them into their own hierarchy.

Every “Thing” node with a parentId value, should nest under the corresponding Thing node.
Every “Foo” node with a parentId value, should nest under the corresponding Foo node — but only within its siblings. The example has two sets of Foo siblings.

I’m trying to create this:

<Xml>
    <Thing id="1" >
        <Foo id="12">
            <Foo id="11" parentId="12"/>
        </Foo>        
        <Thing id="2" parentId="1" >
            <Thing id="3" parentId="2" />
        </Thing>
    </Thing>            
    <Thing id="4" >
        <Foo id="14" parentId="12">
            <Foo id="12" parentId="14"/>
        </Foo>
        <Foo id="15">
            <Foo id="11" parentId="15">
                <Foo id="13" parentId="11"/>
            </Foo>
        </Foo>
    </Thing>
</Xml>

This example comes close:
How can I use XSLT 1.0 to add structure to a non-heirarchal XML file?

I’ve used the identity template to retain all nodes and attributes. Then I want an overriding template to match on all nodes that have a sibling (following or preceding) such that the sibling’s @parentId value equals my @id value. The closest I could come was hard coding an id/parentId value to match on.

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

    <xsl:output indent="yes"/>

    <!-- override identity rule with template to match on
        a node who has siblings, where sibling/@parentId == ./@id
    -->
    <xsl:template match="node()[@id='1' and (preceding-sibling::*[@parentId = 1] or following-sibling::*[@parentId = 1])]">
       <captured>
        <xsl:copy>
            <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>
       </captured>
    </xsl:template>  


    <!-- identity rule -->
    <xsl:template match="@*|node()">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>
    </xsl:template>


</xsl:stylesheet>

I can’t see how to grab the current nodes @id value to use in the predicate of the Xpath matching siblings based on parentId value.

And then I want to nest the current nodes siblings underneath it, where the siblings @ParentId equals my @id.

Answer 1

First of all do notice an error in the provided XML document:

    <Foo id="12" parentId="14"/>
    <Foo id="13" parentId="11"/>
    <Foo id="14" parentId="12"/>

There is a circular relation between Foo with id 12 and Foo with 14. This makes a cycle and isn’t “hierarchy”. Also, these two Foo elements are unreachable from the top of the hierarchy! Please, correct.

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:key name="kElemById" match="*"
   use="concat(generate-id(..), '+', @id)"/>
 <xsl:key match="*" name="kDescendants"
  use="concat(generate-id(key('kElemById', 
                              concat(generate-id(..), '+',@parentId))),
             '+', @parentId)"/>

 <xsl:template match="node()|@*">
     <xsl:copy>
       <xsl:apply-templates select="node()|@*"/>
     </xsl:copy>
 </xsl:template>

 <xsl:template match="/*">
  <Xml>
   <xsl:apply-templates select="*[not(@parentId)]"/>
  </Xml>
 </xsl:template>

 <xsl:template match="*/*">
   <xsl:copy>
    <xsl:apply-templates select="@*"/>

    <xsl:apply-templates select="*[not(@parentId)]"/>

    <xsl:apply-templates select=
       "key('kDescendants', concat(generate-id(), '+',  @id))"/>
  </xsl:copy>
 </xsl:template>
</xsl:stylesheet>

when applied on the provided XML document:

<Xml>
    <Thing id="1"  >
        <Foo id="11" parentId="12"/>
        <Foo id="12"/>
    </Thing>
    <Thing id="2" parentId="1" />
    <Thing id="3" parentId="2" />
    <Thing id="4">
        <Foo id="11" parentId="15"/>
        <Foo id="12" parentId="14"/>
        <Foo id="13" parentId="11"/>
        <Foo id="14" parentId="12"/>
        <Foo id="15"/>
    </Thing>
</Xml>

produces correct result, excluding any unreachable elements:

<Xml>
   <Thing id="1">
      <Foo id="12">
         <Foo id="11" parentId="12"/>
      </Foo>
      <Thing id="2" parentId="1">
         <Thing id="3" parentId="2"/>
      </Thing>
   </Thing>
   <Thing id="4">
      <Foo id="15">
         <Foo id="11" parentId="15">
            <Foo id="13" parentId="11"/>
         </Foo>
      </Foo>
   </Thing>
</Xml>