Bug in Xsl Transformation (unable to return nodelist using choose/where/otherwise in variable)

[Anders Borum]

Hello!

I've come across a strange error that occurs, when you try to return a
nodelist from a variable with a choose/where/otherwise statement.

I'm not quite sure whether it's a bug or simply lack of W3C support. All I
know is, that this Xsl document works with the current implementation of
MSXML V4.0 SP2 if transformed using e.g. VB6. I'm told by the compiler at
runtime, that "the expression should evaluate to a nodeset" (the
choose/where/otherwise part).

What this Xsl document basically does is to look for the parameter
"ImageID". If the ImageID is empty, the first image in the Xml file is
selected. Alternately, the Image matching the parameter "ImageID" is
selected.

The strange part is, that the processor is perfectly capably of computing a
string value in a variable using a choose/where/otherwise part, but not a
nodelist (obviously). I've included the part that fails, as well as the
complete Xsl/Xml listing.

The error is generated only if you reference the beforementioned variable in
the Xsl (e.g. trying to reference an attribute)

This works:
<xsl:variable name="oImage" select="$oImage List[@ImageID = $ImageID]"/>

But this doesn't:
<xsl:variable name="oImage">
<xsl:choose>
<xsl:when test="$ImageID = ''">
<xsl:value-of select="$oImage List[position() = 1]"/>
</xsl:when>
<xsl:otherwis e>
<xsl:value-of select="$oImage List[@ImageID = $ImageID]"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>

-- o --

ImageList.xsl (complete):

<?xml version="1.0" ?>
<xsl:styleshe et
version="1.0"
xmlns:xsl="http ://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" indent="no"/>

<xsl:param name="ImageID"/>

<xsl:variable name="oImageLis t" select="/ImageList/Image"/>
<xsl:variable name="oImage">
<xsl:choose>
<xsl:when test="$ImageID = ''">
<xsl:value-of select="$oImage List[position() = 1]"/>
</xsl:when>
<xsl:otherwis e>
<xsl:value-of select="$oImage List[@ImageID = $ImageID]"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>

<xsl:template match="/">
ImageID is: <xsl:value-of select="$oImage/@ImageID"/>
</xsl:template>
</xsl:stylesheet>
ImageList.xml (short excempt - some elements removed):

<ImageList>
<Image ImageID="1"/>
<Image ImageID="2"/>
<Image ImageID="3"/>
<Image ImageID="4"/>
<Image ImageID="5"/>
</ImageList>

Thanks in advance!

--
venlig hilsen / with regards
anders borum
--

[Oleg Tkachenko]

Anders Borum wrote:

I've come across a strange error that occurs, when you try to return a
nodelist from a variable with a choose/where/otherwise statement. According to your code you are returning not nodelist, but string value.
But this doesn't:
<xsl:variable name="oImage">
<xsl:choose>
<xsl:when test="$ImageID = ''">
<xsl:value-of select="$oImage List[position() = 1]"/> Should be
<xsl:copy-of select="$oImage List[1]"/> </xsl:when>
<xsl:otherwis e>
<xsl:value-of select="$oImage List[@ImageID = $ImageID]"/>

Should be
<xsl:copy-of select="$oImage List[@ImageID = $ImageID]"/>

And once you have a variable that holds result tree fragment (xsl:variable
with content instead of select attribute) you cannot query it by XPath unless
you convert its value to nodeset using msxml:node-set() function.
So try this trick as a workaround:

<xsl:variable name="oImage"
select="$oImage List[1][$ImageID=''] | $oImageList[@ImageID = $ImageID]"/>

--
Oleg Tkachenko
http://www.tkachenko.com/blog
Multiconn Technologies, Israel

[Anders Borum]

Hello Oleg!

Thanks for the quick reply. I'll give it a try at home later. However,
regarding your comments I don't quite agree that I'm returning a string
(rather than a nodelist as requested). Are you sure the <xsl:copy-of/>
approach works compared to <xsl:value-of/>?

And my secondary concern is why this works with e.g. MSXML 4.0 SP2. I'm only
encountering this issue with the .NET framework.

If the <xsl:copy-of/> approach works, it'll be a no-brainer. I'd just like
to know why Microsoft didn't provide the same behaviour in the .NET
framework.

<xsl:variable name="oImage"
select="$oImage List[1][$ImageID=''] | $oImageList[@ImageID =
$ImageID]"/>

Which unfortunately is not what I had in mind (although it probably works).

--
venlig hilsen / with regards
anders borum
--

[Anders Borum]

Hello Oleg!

I'll check into it later and get back to you!

Again thanks for the discussion so far

--
venlig hilsen / with regards
anders borum
--