On 9/27/2008, "Dimitre Novatchev" <dnovatchev@xxxxxxxxx> wrote:

>On Fri, Sep 26, 2008 at 6:30 PM, David Frey <dpfrey@xxxxxxx> 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