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I'm trying to use a user-defined function in XSLT that repeatedly calls the value of a certain string. That string is based on the outcome of an XPath expression that doesn't change within the span of a single function call. I thought it would be a good idea to assign it to a variable rather than look it up over and over again.

Unfortunately, at least in Saxon's implementation, you cannot use an XPath expression requiring a node inside a function, even one based on an absolute path, without first using a throw-away line to let the function know you are discussing the root document rather than some other one.

So, for example, the following code throws an error:

<xsl:function name="udf:LeafMatch">
<xsl:param name="sID"></xsl:param>
<xsl:variable name="myLeaf" select="/potato/stem[@sessionID=$sID][scc]/scc/@leafnumber"/>

Normally, the solution is just to first call any global variable to give context. For example, the following works inside of an udf ($root is a variable identified with the root node):

<xsl:for-each select="$root">
<xsl:value-of select="/potato/stem[@sessionID=$sID][scc]/scc/@leafnumber"/>
</xsl:for-each>

But this doesn't work when trying to use Xpath to fix the value of a variable because I'm not allowed to put the expression within a for-each.

I also tried using 

<xsl:choose><xsl:when select"$root"><xsl:value-of select="/potato/stem[@sessionID=$sID][scc]/scc/@leafnumber"/></xsl:when></xsl:choose>

to give it context, going on what I saw here:http://www.stylusstudio.com/xsllist/200504/post00240.html

That didn't work either.

FWIW, passing the variable into the function is problematic because the Xpath expression used to define "myleaf" depends on the context node, and I don't know how to get Xpath to call one path based on values in the current context node.

For example, in the code calling this function I have something like:

<xsl:for-each select="/potato/stem[eye]">
<leaf = "{udf:LeafMatch(@sessionID)}"/>
</xsl:for-each>

I'm working in the context of a /potato/stem[eye] node and using the udf to look for a /potato/stem[scc] node that has the same value of @sessionID. I don't know how to reference the value of @sessionID from the current context node in the predicate of an XPath searching for other nodes in a completely different part of the XML tree, so I was using a udf to do that. It was working fine until I decided to try to use a variable for the string rather than having the processor look it up each time.

I was trying to avoid going one level deeper (having my function itself call a named template or putting a named template inside my original for-each and having that named template call a function).

So my questions are:

A. For a user-defined function, how do I set a variable that depends on an XPath expression?

B. Is there a snazzy way in Xpath to use values drawn from the current content node in the predicates of the Xpath expression you are trying to test?

Brian Tompsett - 汤莱恩
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David R
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  • @_David R: Unfortunately it is difficult to understand the question. Could you, please, edit the question and provide a complete (but short) example, so that it can be reproduced? Also, please, tell us exactly what you want to achieve. Also, please, provide the corresponding (as short as possible) complete source XML document. In particular, what is the meaning of "trying to use Xpath to fix the value of a variable"? – Dimitre Novatchev Oct 28 '11 at 04:34
  • I have posted an example with the relevant XML on a different question focusing on just the question of how to use attributes related to the current node (say in an for-each clause) in an XPath expression searching out another one. That question is here [link](http://stackoverflow.com/questions/7926680/xslt2-how-to-reference-attributes-about-the-current-node-in-xpath2-predicates) – David R Oct 28 '11 at 08:12
  • @_David R: Thanks, I have answered the new question. – Dimitre Novatchev Oct 28 '11 at 12:35

1 Answers1

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So my questions are:

A. For a user-defined function, how do I set a variable that depends on an XPath expression?

B. Is there a snazzy way in Xpath to use values drawn from the current content node in the predicates of the Xpath expression you are trying to test?

Both questions are quite unclear.

A: I assume you actually mean:

"Inside an xsl:function how do I define a variable that depend on the context node?"

The answer: You can't. By definition there is no context node within an xsl:function. This is defined by the W3C XSLT 2.0 specification in the following way:

"Within the body of a stylesheet function, the focus is initially undefined; this means that any attempt to reference the context item, context position, or context size is a non-recoverable dynamic error. [XPDY0002]"

You can, however, pass as a parameter the intended context node (or just the document node that must be used as current). Or, alternatively, you may refer to a globally defined variable.

B: This question is completely not understandable:

  1. What is "snazzy"?

  2. What is "current content node"? Please, provide an example of a specific task to be accomplished in the wanted "snazzy" way.

Dimitre Novatchev
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  • Thanks for answering the first question. With regard to spelling out my request for the second, details are here: That question is here [link](http://stackoverflow.com/questions/7926680/xslt2-how-to-reference-attributes-about-the-current-node-in-xpath2-predicates) – David R Oct 28 '11 at 08:13