XSLT match based on concatenating two node values - xslt

Question

If I have xml that looks like this
<Msg>
<Payload role="s">
<row>
<venue>XDM</venue>
<account>60190</account>
</row>
</Payload>
<Payload role="c" id="atom1">
<ResultSet>
<Row>
<U_LegAcc>XDM60190</U_LegAcc>
<U_AccCod>SYS00000000508</U_AccCod>
</Row>
</ResultSet>
</Payload>
</Msg>
I need to get the U_AccCod node value based on the U_LegAcc which is matched to the concatenated value of venue (XDM) & account (61090) i.e. XDM61090
How can I get xml that looks like this.
<Msg>
<Payload>
<row>
<venue>XDM</venue>
<account>60190</account>
<U_AccCod>SYS00000000508</U_AccCod>
</row>
</Payload>
</Msg>
I have tried simplifying it and removing the concatenation just to get a start but I can't even get that to work, i.e. <account> and <U_AccCod> are the same. I have tried using a key but I am not getting any output
<xsl:key name="sapaccount" match="ResultSet" use="U_LegAcc" />
<xsl:template match="Row" mode="name">
<xsl:value-of select="U_AccCod" />
</xsl:template>
<xsl:template match="row/account">
<xsl:apply-templates select="key('sapaccount', .)" mode="name" />
</xsl:template>

Answer 1

There is actually no reason why you can't continue to use the key here. They are generally more efficient to use to look up elements. The problem with your current key is that is not quite correct. You are currently looking for ResultSet elements by means of the U_LegAcc value, but U_LegAcc is not a direct child of ResultSet, but of Row, so you probably want to define your key like so:
<xsl:key name="sapaccount" match="ResultSet/Row" use="U_LegAcc" />
Or maybe just this, if Row elements can only occur in one place
<xsl:key name="sapaccount" match="Row" use="U_LegAcc" />
Then, to look up the value, if positioned on a account element, you would do this:
<xsl:apply-templates select="key('sapaccount', concat(preceding-sibling::venue, .))" />
Or better still, have a template to match the row element, and then you can do this
<xsl:apply-templates select="key('sapaccount', concat(venue, account))" />
Try this XSLT
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:key name="sapaccount" match="Row" use="U_LegAcc"/>
<xsl:template match="Payload[#role='s']">
<Payload>
<xsl:apply-templates/>
</Payload>
</xsl:template>
<xsl:template match="Payload[#role='c']"/>
<xsl:template match="row">
<row>
<xsl:apply-templates/>
<xsl:apply-templates select="key('sapaccount', concat(venue, account))/U_AccCod"/>
</row>
</xsl:template>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
When applied to your XML, the following is output
<Msg>
<Payload>
<row>
<venue>XDM</venue>
<account>60190</account>
<U_AccCod>SYS00000000508</U_AccCod>
</row>
</Payload>
</Msg>

Answer 2

In the part of your XSL which is emitting the row element from the same element in the input:
<xsl:template match="row">
<row>
<xsl:copy-of select="venue"/>
<xsl:copy-of select="account"/>
<U_AccCod>
<xsl:variable name="this" select="."/>
<xsl:value-of select="/Msg/Payload/ResultSet/Row/U_AccCod[../U_LegAcc=concat($this/venue,$this/account)]"/>
</U_AccCod>
</row>
</xsl:template>
Untested, may need tweaking.