Two ways to set a variable to a temp result, why does one work and the other not?

mphare · March 4th, 2011, 03:04 PM

I am using Saxon 9 EE with Oxygen XML 12.1

I an trying to set a variable to a temporary result and I have a way that works, and a way that does not. When I dump the results, they look the same to me. I cannot figure out why one works and the other doesn't.

This way works:

Code:

<xsl:variable name="iterdef"
            select="nmirepo:findIteratorDef($myData/IteratorTagRef[1]/@Idref)"/>

This way does not:

Code:

<xsl:variable name="iterdefx">
   <xsl:sequence select="nmirepo:findIteratorDef($myData/IteratorTagRef[1]/@Idref)"></xsl:sequence>
</xsl:variable>

When I dump using:

Code:

<xsl:message>
   [iterdef]
   <xsl:sequence select="$iterdef"></xsl:sequence>
   [iterdefx]
   <xsl:sequence select="$iterdefx"></xsl:sequence>
   [-----]
</xsl:message>

I get:

Code:

                        [iterdef]
                        <IteratorDef xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><IteratorTag Id="BABEGAJE">allOCn</Iterat
orTag><IteratorList><IteratorChoice>3</IteratorChoice><IteratorChoice>12</IteratorChoice><IteratorChoice>48</IteratorChoice><Iterato
rChoice>192</IteratorChoice></IteratorList></IteratorDef>
                        [iterdefx]
                        <IteratorDef xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><IteratorTag Id="BABEGAJE">allOCn</Iterat
orTag><IteratorList><IteratorChoice>3</IteratorChoice><IteratorChoice>12</IteratorChoice><IteratorChoice>48</IteratorChoice><Iterato
rChoice>192</IteratorChoice></IteratorList></IteratorDef>
                        [-----]

Which looks identical to me (do you see any differences?)

I have not included the findIteratorDef() code, it basically dereferences the Idref tag and returns what it finds as the temporary result that you see in the output.

If I pass on the $iterdef content to the rest of my code it works the way I expected it to. If I pass $iterdefx content, it does not. It basically acts as though I passed nothing at all.

My question is, are the two ways I'm setting the variables equivalent?
(I'm guessing not since I do not get equivalent results)
So, besides what I see visually by using xsl:message to dump to my display, what else can be different with the two version of the variables that is unseen?

mhkay · March 4th, 2011, 07:46 PM

When you use the select attribute of xsl:variable, the variable contains references to the original nodes. When you use a contained child element (and no "as" attribute on the xsl:variable) a new temporary tree is created containing a copy of the selected nodes. The copy looks the same if serialized, but the variable doesn't contain the original nodes. The most obvious way of seeing the difference is by navigating upwards from the selected node: in the first case $var/ancestor::* will select all the ancestor elements in the node's original tree; in the second case $var/ancestor::* will find nothing, because the copied node has no ancestors.

You'll find all this explained in great detail in the xsl:variable section of my book.

mphare · March 5th, 2011, 12:27 AM

Thanks, Michael. I'll take a look at the xsl:variable section a little closer.
I'm still coming to terms regarding the difference between xsl:copy-of and xsl:sequence.. I thought using xsl:sequence solved the problem you are describing. But I will read the section in more detail.

Thanks again, and have a nice weekend!