XMLT : replace values with values found in another xml - xslt

Question

I have a file called ori.xml:
<?xml version="1.0" encoding="UTF-8"?>
<root>
<container>
<elA>
<el1>value1</el1>
<el2>value2</el2>
</elA>
<elB>
<el3>value3</el3>
<el4>value4</el4>
<el5>value5</el5>
</elB>
<elC>
<el6>value5</el6>
</elC>
</container>
</root>
and another one called modifs.xml:
<?xml version="1.0" encoding="UTF-8"?>
<els>
<el2>newvalue2</el2>
<el5>newvalue5</el5>
</els>
and I would like to obtain result.xml:
<?xml version="1.0" encoding="UTF-8"?>
<root>
<container>
<elA>
<el1>value1</el1>
<el2>newvalue2</el2>
</elA>
<elB>
<el3>value3</el3>
<el4>value4</el4>
<el5>newvalue5</el5>
</elB>
<elC>
<el6>value5</el6>
</elC>
</container>
</root>
I'm a beginner in XSLT.
So I started to write a stylesheet with which I'm able to change value2 into newvalue2:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:param name="fileName" select="'modifs.xml'" />
<xsl:param name="modifs" select="document($fileName)" />
<xsl:param name="updateEl" >
<xsl:value-of select="$modifs/els/el2" />
</xsl:param>
<xsl:template match="#* | node()">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="//elA/el2">
<xsl:copy>
<xsl:apply-templates select="$updateEl" />
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
But now I have to modify this stylesheet to be able to know which elements are in modifs.xml and find them in ori.xml. I don't know how to do that. Could you help please ?

Answer 1

I would use a key:
<xsl:key name="ref-change" match="els/*" use="local-name()"/>
<xsl:template match="*[key('ref-change', local-name(), $modifs)]">
<xsl:copy-of select="key('ref-change', local-name(), $modifs)"/>
</xsl:template>
However, using the third argument for the key function is only supported in XSLT 2 and later thus if you use an XSLT 1 processor you need to move the logic into the template, that requires using for-each to "switch" the context document
<xsl:template match="*">
<xsl:variable name="this" select="."/>
<xsl:for-each select="$modifs">
<xsl:choose>
<xsl:when test="key('ref-change', local-name($this))">
<xsl:copy-of select="key('ref-change', local-name($this))"/>
</xsl:when>
<xsl:otherwise>
<xsl:for-each select="$this">
<xsl:call-template name="identity"/>
</xsl:for-each>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
</xsl:template>
Put name="identity" on your identity transformation template.