How do I get an XML node with xpath in a loop, based on an attribute with the same name as the attribute in the tree I'm searching? - xslt

Question

I cant really formulate that better, so I'll go with an example instead:
XML:
<root>
<foo>
<bar id="1">sdf</bar>
<bar id="2">sdooo</bar
</foo>
<feng>
<heppa id="4">hihi</heppa>
<heppa id="2">sseeapeea</heppa>
<heppa id="1">....</heppa>
</feng>
</root>
XSLT:
<xsl:for-each select="/root/foo/bar">
<p>
<xsl:value-of select="." />: <xsl:value-of select="/root/feng/heppa[#id = #id]" />
</p>
</xsl:for-each>
Desired output:
<p>sdf: ....</p>
<p>sdooo: sseeapeea</p>
Actual output:
<p>sdf: hihi</p>
<p>sdooo: hihi</p>

Answer 1

For selecting nodes with XPath 1.0 only, you need to do a node set comparison:
/root/feng/heppa[#id=/root/foo/bar/#id]
Of course, this has NxM complexity (as the others XSLT solutions)
With XSLT 1.0 you should use keys because there are cross references:
<xsl:key name="kBarById" select="bar" use="#id"/>
<xsl:template match="/root/feng/heppa[key('kBarById',#id)]">
<p>
<xsl:value-of select="concat(key('kBarById',#id),': ',.)"/>
</p>
</xsl:template>

Answer 2

I assume you mean /root/foo/bar since /root/foo elements don't have id.
You're comparing the #id with itself, so of course it's true for the first node examined. You can use current() to reference the current node in an expression:
<xsl:for-each select="/root/foo/bar">
<p>
<xsl:value-of select="." />: <xsl:value-of select="/root/feng/heppa[#id = current()/#id]" />
</p>
</xsl:for-each>

Answer 3

Another solution is to read the id attribute into a variable.
<xsl:for-each select="/root/foo/bar">
<xsl:variable name="id" select="#id"/>
<p>
<xsl:value-of select="." />: <xsl:value-of select="/root/feng/heppa[#id = $id]" />
</p>
</xsl:for-each>
This might be handier, if your real use case is more complicated and you need to use the value of the id multiple times in this for-each section.