Flat xml to hierarchical XML transformation using XSLT - xslt

Question

I am trying to create a transformation that will map a flat structure ( with parent/child ids) into a hierarchical structure. I have included a simple request and responses examples below. The actual data has over 500 elements. Any help would be really appreciated! Thanks!
Validation Rules:
Offer can be in top level
Offer can be under package
Offer can be under group
Request:
<!-- offer with no parents(group or package) if No package_id or group ID in ffer element-->
<offer>
<namevaluepair>
<name>type</name>
<value>offer</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>OFR1</value>
</namevaluepair>
</offer>
<!-- type package P1 & P2 representation-->
<offer>
<namevaluepair>
<name>type</name>
<value>package</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>P1</value>
</namevaluepair>
</offer>
<offer>
<namevaluepair>
<name>type</name>
<value>package</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>P2</value>
</namevaluepair>
</offer>
<!-- offer under package but not in group-->
<offer>
<namevaluepair>
<name>type</name>
<value>offer</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>OFRP1</value>
</namevaluepair>
<namevaluepair>
<name>package_id</name>
<value>P1</value>
</namevaluepair>
</offer>
<!-- offers under package but not in group-->
<offer>
<namevaluepair>
<name>type</name>
<value>offer</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>OFRP2</value>
</namevaluepair>
<namevaluepair>
<name>package_id</name>
<value>P2</value>
</namevaluepair>
</offer>
<!-- type groups G1P1 and G1P2 representations,
group G1P1 is part of package P1 and this group G1P2 is part of package P2-->
<offer>
<namevaluepair>
<name>type</name>
<value>group</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>G1P1</value>
</namevaluepair>
<namevaluepair>
<name>package_id</name>
<value>P1</value>
</namevaluepair>
</offer>
<offer>
<namevaluepair>
<name>type</name>
<value>group</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>G2P2</value>
</namevaluepair>
<namevaluepair>
<name>package_id</name>
<value>P2</value>
</namevaluepair>
</offer>
<!-- offer OFRG1P1 under group G1P1 as parent AND G1P1 is under P1 package-->
<offer>
<namevaluepair>
<name>type</name>
<value>offer</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>OFRG1P1</value>
</namevaluepair>
<namevaluepair>
<name>group_id</name>
<value>G1P1</value>
</namevaluepair>
</offer>
<!-- offer OFRG1P1 under group G2P2 as parent AND grp G2P2 is under P2 package-->
<offer>
<namevaluepair>
<name>type</name>
<value>offer</value>
</namevaluepair>
<namevaluepair>
<name>id</name>
<value>OFRG2P2</value>
</namevaluepair>
<namevaluepair>
<name>group_id</name>
<value>G2P2</value>
</namevaluepair>
</offer>
Output:
<offers>
<!-- offer with no parents(group or package)-->
<offer ID="OFR1"/>
<packages>
<package ID="P1">
<groups>
<group ID="G1P1">
<offer ID="OFRG1P1"/>
</group>
</groups>
<offer ID="OFR1P1"/>
</package>
<package ID="P2">
<groups>
<group ID="G2P2">
<offer ID="OFRG2P2"/>
</group>
</groups>
<offer ID="OFR1P2"/>
</package>
</packages>
</offers>

Answer 1

Here is a XSLT 1.0 solution, utilizing keys.
The stylesheet declares four keys for finding different objects:
top level objects by their type (package or offer),
groups by their package id,
offers belonging to a package by their package id, and
offers belonging to a group by their group id.
At the top level, the stylesheet processes the top-level offers and packages. At the package level, the stylesheet processes the groups and offers belonging to that package. At the group level, the system processes the offers belonging to that group.
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:key name="top-level-objects-by-type"
match="offer[not(namevaluepair[name='package_id'])]
[not(namevaluepair[name='group_id'])]"
use="namevaluepair[name='type']/value"/>
<xsl:key name="groups-by-package-id"
match="offer[namevaluepair[name='type' and value='group']]"
use="namevaluepair[name='package_id']/value"/>
<xsl:key name="offers-by-package-id"
match="offer[namevaluepair[name='type' and value='offer']]"
use="namevaluepair[name='package_id']/value"/>
<xsl:key name="offers-by-group-id"
match="offer[namevaluepair[name='type' and value='offer']]"
use="namevaluepair[name='group_id']/value"/>
<xsl:template match="/">
<offers>
<xsl:apply-templates select="key('top-level-objects-by-type', 'offer')"/>
<packages>
<xsl:apply-templates select="key('top-level-objects-by-type', 'package')"/>
</packages>
</offers>
</xsl:template>
<xsl:template match="offer[namevaluepair[name='type' and value='package']]">
<xsl:variable name="id" select="namevaluepair[name='id']/value"/>
<package ID="{$id}">
<groups>
<xsl:apply-templates select="key('groups-by-package-id', $id)"/>
</groups>
<xsl:apply-templates select="key('offers-by-package-id', $id)"/>
</package>
</xsl:template>
<xsl:template match="offer[namevaluepair[name='type' and value='group']]">
<xsl:variable name="id" select="namevaluepair[name='id']/value"/>
<group ID="{$id}">
<xsl:apply-templates select="key('offers-by-group-id', $id)"/>
</group>
</xsl:template>
<xsl:template match="offer[namevaluepair[name='type' and value='offer']]">
<offer ID="{namevaluepair[name='id']/value}"/>
</xsl:template>
</xsl:stylesheet>