Question

I have faced an issue when using a variable as a condition for XPath evaluation. I have the following template which works fine:

<xsl:template name="typeReasonDic">
    <xsl:variable name="dic" select="$schema//xs:simpleType[@name = 'type_reason_et']"/>
    <!-- do something with the variable -->
</xsl:template>

However, when I change it to look like this:

<xsl:template name="typeReasonDic">
    <xsl:param name="choose_dic" select="@name = 'type_reason_et'"/>

    <xsl:variable name="dic" select="$schema//xs:simpleType[$choose_dic]"/>
    <!-- do something with the variable -->
</xsl:template>

it fails to find the desired node.

What I wish to get is a template with a default value for $choose_dic which can be overriden where necessary.

What am I missing here?

UPD: there is this link I found with the description of what I’m trying to do, but it doesn’t seem to work for me.

Answer 1

You can’t do this directly in XSLT 1.0 or 2.0 without an extension function. The problem is that with

<xsl:template name="typeReasonDic">
    <xsl:param name="choose_dic" select="@name = 'type_reason_et'"/>

    <xsl:variable name="dic" select="$schema//xs:simpleType[$choose_dic]"/>
    <!-- do something with the variable -->
</xsl:template>

the <xsl:param> will evaluate its select expression a single time in the current context and store the true/false result of this evaluation in the $choose_dic variable. The <xsl:variable> will therefore select either all xs:simpleType elements under the $schema (if $choose_dic is true) or none of them (if $choose_dic) is false. This is very different from

<xsl:variable name="dic" select="$schema//xs:simpleType[@name = 'type_reason_et']"/>

which will evaluate @name = 'type_reason_et' repeatedly, in the context of each xsl:simpleType, and select those elements for which the expression evaluated to true.

If you store the XPath expression as a string you can use an extension function such as dyn:evaluate or the XSLT 3.0 xsl:evaluate element if you’re using Saxon.