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The problem is to merge and sort multiple XML files with XSL and output valid HTML, viewable with Firefox >=3.5 and if possible IE >=7. The answer should be as simple as possible (performance is not important).
File a.xml
<?xml version="1.0"?>
<root>
<tag>cc</tag>
<tag>aa</tag>
</root>
File b.xml
<?xml version="1.0"?>
<root>
<tag>xx</tag>
<tag>bb</tag>
</root>
File index.xml
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="merge.xslt"?>
<list>
<entry>a.xml</entry>
<entry>b.xml</entry>
</list>
File merge.xslt
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:ph="http://ananas.org/2003/tips/photo">
<xsl:output method="html"/>
<xsl:template match="list">
<html>
<body>
<xsl:apply-templates/>
</body>
</html>
</xsl:template>
<xsl:template match="entry">
<xsl:for-each select="document(.)/root/tag">
<!-- This will only sort the values of a single file -->
<xsl:sort select="." data-type="text" order="ascending" />
- <xsl:value-of select="."/> <br/>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
Current output:
aa
cc
bb
xx
Expected output:
aa
bb
cc
xx
882
The solution to this is a very short and easy transformation (absolutely no extension functions are required!):
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/*">
<html>
<ul>
<xsl:apply-templates
select="document(entry)/*/tag">
<xsl:sort/>
</xsl:apply-templates>
</ul>
</html>
</xsl:template>
<xsl:template match="tag">
<li><xsl:value-of select="."/></li>
</xsl:template>
</xsl:stylesheet>
when this transformation is applied on the provided index.xml file:
<list>
<entry>a.xml</entry>
<entry>b.xml</entry>
</list>
the wanted, correct result is produced:
<html>
<ul>
<li>aa</li>
<li>bb</li>
<li>cc</li>
<li>xx</li>
</ul>
</html>
and it is displayed in any browser as:
Explanation: This solution uses the power of the standard XSLT function document(). As defined in the W3C XSLT 1.0 Recommendation:
When the document function has exactly one argument and the argument is a node-set, then the result is the union, for each node in the argument node-set, of the result of calling the document function with the first argument being the string-value of the node
This explains the effect of this fragment from our code:
<xsl:apply-templates
select="document(entry)/*/tag">
<xsl:sort/>
</xsl:apply-templates>
What happens here is that the argument to the document() function is the node-set of all entry children of the top element of index.xml. The result is the union of all document nodes.
Therefore:
select="document(entry)/*/tag"
selects all tag elements in all documents referenced in index.xml. Then they are sorted (by xsl:sort) and each of the element of the already sorted nodelist is processed by the template matching tag.
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