xslt to add default value where element doesn't exist - xslt

Question

I'm struggling with trying to test to see if an element exists. If it doesn't, I'd like to add in a default value. Here's my XML
<records>
<record>
<InstanceData>
<instance>
<FirstName>Johhny</FirstName>
<LastName>Jenkins</LastName>
<AlbumCount>3</AlbumCount>
</instance>
</InstanceData>
</record>
<record>
<InstanceData>
<instance>
<FirstName>Art</FirstName>
<LastName>Tatum</LastName>
<AlbumCount>7</AlbumCount>
</instance>
</InstanceData>
</record>
<record>
<InstanceData>
<instance>
<FirstName>Count</FirstName>
<LastName>Basie</LastName>
</instance>
</InstanceData>
</record>
</records>
I'd like to be able to copy over existing values and set any record without the Album Count element to <AlbumCount>0</AlbumCount>. This is the xslt I've been working with but I think I'm some way off the mark.
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:template match="Records">
<xsl:for-each select="node()">
<xsl:choose>
<xsl:when test="name()='AlbumCount'">
<xsl:element name="AlbumCount">
<xsl:choose>
<xsl:when test="name()='AlbumCount'">
<xsl:copy-of select=".">
</xsl:copy-of>
</xsl:when>
<xsl:otherwise>
<AlbumCount>0</AlbumCount>
</xsl:otherwise>
</xsl:choose>
</xsl:element>
</xsl:when>
<xsl:otherwise>
<xsl:copy-of select=".">
</xsl:copy-of>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
Thanks for looking.

Answer 1

Try this:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes" omit-xml-declaration="no"/>
<!-- identity template -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="instance[not(AlbumCount)]">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
<AlbumCount>0</AlbumCount>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
Start with the identity transformation, then just handle the exception differently.

Answer 2

You test for the existance of an element simply with the elements name, for example:
<xsl:if test="not(AlbumCount)">
<AlbumCount>0</AlbumCount>
</xsl:if>
The simpler way to do what you want is to use the standard copy template combined with a special rule for places where AlbumCount elements need adding:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl">
<xsl:output method="xml" indent="yes"/>
<!-- Standard copy template -->
<xsl:template match="#* | node()">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
</xsl:copy>
</xsl:template>
<!-- Special template to add AlbumCount elements where required -->
<xsl:template match="records/record/InstanceData/instance">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
<xsl:if test="not(AlbumCount)">
<AlbumCount>0</AlbumCount>
</xsl:if>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>