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<< XQuery .NET and XML >>

By	Dimitre Novatchev
First Posted	01/04/2003
Times viewed	977

The Magic of xsl:key

Summary Demonstrates the power of using xsl:key and the key() function in the sort of two lists of objects (containers and items-contained) connected with a many-to-many relationship.

From microsoft.public.xsl: "I have a sorting problem. If I have this XML (two lists of items, with entries denoting a many-to-many relationship between them)". The source xml document is in the xml-code section below. "And I want to see it as (Container, sorted alphabetically, with the related items as child elements, sorted alphabetically - but NOT a direct copy of either Containers or Items)" The wanted result is in the xml-code section. The solution is in the XSLT-code section. It demonstrates the power of using xsl:key and the key() function in the sort of two lists of objects (containers and items-contained) connected with a many-to-many relationship. Firstly, the "contents" elements are grouped by the "cid" attribute -- the ID of the container they point to. This is an implementation of the Muenchian method for grouping. Then they are sorted by the container name, again obtained as value of the key() function using the @cid attribute's value. With each such sorted element, a "container element is created that has a text node -- the value of the "containername" child of the corresponding "container" element (using again the key() function) and with "item" elements as children -- the items contained in this container, as specified in the (possibly many) "contents" elements. This is done in a double application of the key() function: key('kItem', key('kContents',@cid)/@iid) Here one of the most powerful features of the key() function is used, that its second argument can be a node-set and in this case the corresponding matching nodes for every node in the node-set argument are generated. Do enjoy, Dimitre Novatchev.

Additional information
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output omit-xml-declaration="yes" indent="yes"/> <xsl:key name="kContainerName" match="containername" use="../@cid"/> <xsl:key name="kContents" match="contents" use="@cid"/> <xsl:key name="kItem" match="itemname" use="../@iid"/> <xsl:template match="/"> <xsl:for-each select="*/contents[generate-id() = generate-id(key('kContents', @cid )[1~ ) ~"> <xsl:sort select="key('kContainerName', @cid)"/> <container> <xsl:value-of select="key('kContainerName', @cid)"/> <xsl:for-each select="key('kItem', key('kContents',@cid)/@iid )"> <xsl:sort/> <item><xsl:value-of select="."/></item> </xsl:for-each> </container> </xsl:for-each> </xsl:template> </xsl:stylesheet>

Further additional information
 <root> <container cid="1"> <containername>A</containername> </container> <container cid="2"> <containername>C</containername> </container> <container cid="3"> <containername>B</containername> </container> <item iid="1"> <itemname>c</itemname > </item> <item iid="2"> <itemname>a</itemname > </item> <item iid="3"> <itemname>b</itemname > </item> <contents cid="1" iid="1"/> <contents cid="1" iid="3"/> <contents cid="2" iid="1"/> <contents cid="2" iid="3"/> <contents cid="2" iid="2"/> <contents cid="3" iid="3"/> <contents cid="3" iid="2"/> <contents cid="3" iid="1"/> </root>  <Container>A <item>b</item> <item>c</item> </container> <Container>b <item>a</item> <item>b</item> <item>c</item> </container> <Container>c <item>a</item> <item>b</item> <item>c</item> </container>

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