XSLT for replace attribute in XML element if it exists in another XML?

Question

I have 2 files

catalog.xml

Answer 1

The following transform, uses catalog.xml as input and loads vinyl.xml using document(). It performs the merge just by making a simple test.

---

[XSLT 1.0]

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output indent="yes"/>
    <xsl:variable name="vinyl" select="document('test_i2.xml')"/>

    <xsl:template match="node()|@*">
        <xsl:copy>
            <xsl:apply-templates select="node()|@*"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="@vinyl">
        <xsl:attribute name="vinyl">
            <xsl:variable name="test" select="
                 $vinyl/Vinyl/Album[Title=current()/../@Title]/Vinyl"/>
            <xsl:choose>
                <xsl:when test="$test">
                    <xsl:value-of select="$test"/>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:value-of select="."/>
                </xsl:otherwise>
            </xsl:choose>
        </xsl:attribute>
    </xsl:template>

</xsl:stylesheet>

---

This template for the attribute is less immediate, but it exploits pure XPath:

<xsl:template match="@vinyl">
    <xsl:attribute name="vinyl">
        <xsl:value-of select="
          $vinyl/Vinyl/Album[Title=current()/../@Title]/Vinyl
          |
          self::node()[count($vinyl/Vinyl/Album[Title=current()/../@Title])=0]"/>
    </xsl:attribute>
</xsl:template>