XSL evaluate dynamic XPATH from another document - xslt

Question

I have two sample documents defined below. In module_meta.xml only the effect nodes on xpath /mdata/effectivity are relevant. As seen below, they contain a path attribute and a effrg attribute. The goal is now to evaluate the xpath (which is defined in the module_meta.xml as the path attribute) on the module.xml and append the effrg to it. See desired_output.xml for the desired result. The xsl transformation is applied on module.xml. I know that I have to use the document() function to "include" module_meta.xml, but so far I am at a loss.
module.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE proc>
<procbody>
<info>
<action lid="a">
</action>
<action lid="b">
</action>
<action lid="c">
</action>
</info>
</procbody>
module_meta.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mdata>
<mdata>
<metadata>
<metadata-item name="n1" value="v1" />
<metadata-item name="n2" value="v2" />
<metadata-item name="n3" value="v3" />
</metadata>
<effectivity>
<effect path="//*[#lid='a']" effrg="0074 0080 0087" />
<effect path="//*[#lid='b']" effrg="0136 0146 0174" />
</effectivity>
</mdata>
desired_output.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE proc>
<procbody>
<info>
<action lid="a" effrg="0074 0080 0087">
</action>
<action lid="b" effrg="0136 0146 0174">
</action>
<action lid="c">
</action>
</info>
</procbody>

Answer 1

In XSLT 3 with xsl:evaluate support:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="3.0"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="#all"
xmlns:mf="http://example.com/mf"
expand-text="yes">
<xsl:function name="mf:evaluate" as="element(action)?">
<xsl:param name="effect" as="element(effect)"/>
<xsl:evaluate xpath="$effect/#path" context-item="$main-doc"/>
</xsl:function>
<xsl:variable name="main-doc" select="/"/>
<xsl:mode on-no-match="shallow-copy"/>
<xsl:template match="info/action">
<xsl:copy>
<xsl:apply-templates select="#*, $meta//effect[current() is mf:evaluate(.)]/#effrg"/>
</xsl:copy>
</xsl:template>
<xsl:param name="meta">
<mdata>
<metadata>
<metadata-item name="n1" value="v1" />
<metadata-item name="n2" value="v2" />
<metadata-item name="n3" value="v3" />
</metadata>
<effectivity>
<effect path="//*[#lid='a']" effrg="0074 0080 0087" />
<effect path="//*[#lid='b']" effrg="0136 0146 0174" />
</effectivity>
</mdata>
</xsl:param>
</xsl:stylesheet>
For self-containedness of the example the second document is inline as a parameter but you can of course use <xsl:param name="meta" select="doc('module_meta.xml')"/> instead.
It might be much more efficient to use the xsl:evaluate only once for each effect element, for instance, by declaring a key doing that, and store the generated-id if there is one:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="3.0"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="#all"
xmlns:mf="http://example.com/mf"
expand-text="yes">
<xsl:key name="ref" match="mdata/effectivity/effect">
<xsl:variable name="referenced-node" as="node()?">
<xsl:evaluate xpath="#path" context-item="$main-doc" as="node()?"/>
</xsl:variable>
<xsl:sequence select="generate-id($referenced-node)"/>
</xsl:key>
<xsl:variable name="main-doc" select="/"/>
<xsl:mode on-no-match="shallow-copy"/>
<xsl:template match="info/action">
<xsl:copy>
<xsl:apply-templates select="#*, key('ref', generate-id(), $meta)/#effrg"/>
</xsl:copy>
</xsl:template>
<xsl:param name="meta">
<mdata>
<metadata>
<metadata-item name="n1" value="v1" />
<metadata-item name="n2" value="v2" />
<metadata-item name="n3" value="v3" />
</metadata>
<effectivity>
<effect path="//*[#lid='a']" effrg="0074 0080 0087" />
<effect path="//*[#lid='b']" effrg="0136 0146 0174" />
</effectivity>
</mdata>
</xsl:param>
</xsl:stylesheet>
If you want to match any element referenced in the other document and copy any attribute but the path one you could change the template having match="info/action" to
<xsl:template match="*[key('ref', generate-id(), $meta)]">
<xsl:copy>
<xsl:apply-templates select="#*, key('ref', generate-id(), $meta)/(#* except #path), node()"/>
</xsl:copy>
</xsl:template>