On 9/27/2008, "Dimitre Novatchev" <dnovatchev(_at_)gmail(_dot_)com> wrote:
On Fri, Sep 26, 2008 at 6:30 PM, David Frey <dpfrey(_at_)shaw(_dot_)ca> wrote:
I have an XSLT 1 question.
Say I have:
<xsl:variable name="foo">
<xsl:choose>
<xsl:when test="$aVar='someFlag'">
<xsl:value-of select="/path/to/some/element"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="/path/to/another/element"/>
</xsl:otherwise>
</xsl:variable>
<xsl:choose>
<xsl:when test="$foo">
<xsl:value-of select="$foo"/>
</xsl:when>
<xsl:otherwise>--</xsl:otherwise>
</xsl:choose>
Currently, I never get "--" as my output even if $aVar is set to
'someFlag' and the element at "/path/to/some/element" does not exist.
Can someone explain where I went wrong?
The variable $foo is of type RTF (Result Tree Fragment).
The XSLT 1.0 spec says:
"A result tree fragment represents a fragment of the result tree. A
result tree fragment is treated equivalently to a node-set that
contains just a single root node" ...
and a few lines later:
"When a permitted operation is performed on a result tree fragment, it
is performed exactly as it would be on the equivalent node-set."
http://www.w3.org/TR/xslt#section-Result-Tree-Fragments
The <xsl:when/> is evaluated as per spec:
"When an xsl:choose element is processed, each of the xsl:when
elements is tested in turn, by evaluating the expression and
converting the resulting object to a boolean as if by a call to the
boolean function."
http://www.w3.org/TR/xslt#section-Conditional-Processing-with-xsl:choose
this means that the value of
boolean($foo)
is determined and it is the same as when boolean() is applied on the
equivalent node-set of the RTF $foo.
Because the equivalent node-set of an RTF always consists of just one
node (a root node), and the rules for boolean() say:
"a node-set is true if and only if it is non-empty"
http://www.w3.org/TR/xpath#section-Boolean-Functions
this means that boolean($foo) is always true().
This is why, the first <xsl:when> in the code in question is always chosen:
<xsl:choose>
<xsl:when test="$foo">
<xsl:value-of select="$foo"/>
</xsl:when>
<xsl:otherwise>--</xsl:otherwise>
</xsl:choose>
and the <xsl:otherwise> above is never chosen.
Thanks for the detailed explanation. It sounds like the approach I was
using will not work. Is there another way that I can write this
template?
Basically, I want a template that will output the text of a node for an
arbitrary XPath if that node exists. If the node doesn't exist, I want
it to produce "--".
Thanks,
David
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