Predicate question

pdamer · November 19th, 2003, 10:30 AM

My transform seems to be working but I want to make sure this does what I think it does.

I have a document with one or more "meeting_pattern" elements, some of which may have a "topic" child element. After displaying other information from each meeting pattern I want to display the "topic" from the first meeting pattern that has a "topic" child.

Should this do that?
<other stuff>
<xsl:apply-templates select="meeting_pattern[topic][position() = 1] mode ="topic"/>
<xsl:template match="meeting_pattern" mode="topic">
<xsl:value-of select="topic"/>
</xsl:template>

joefawcett · November 19th, 2003, 11:02 AM

Depends on the structure of your file. If all meeting_pattern elements are siblings it does not matter, if they are not it might. Example:

Code:

<meetings>
  <meeting>
   <meeting_pattern><topic>A</topic></meeting_pattern>
  </meeting>
  <meeting>
   <meeting_pattern></meeting_pattern>
  </meeting>
  <meeting>
   <meeting_pattern><topic>B</topic></meeting_pattern>
   <meeting_pattern><topic>C</topic></meeting_pattern>
  </meeting>
  <meeting>
   <meeting_pattern><topic>D</topic></meeting_pattern>
  </meeting>
  <meeting>
   <meeting_pattern></meeting_pattern>
  </meeting>
</meetings>

When you ask for "/meetings/meeting/meeting_pattern[topic][1]" you are asking for all meeting_pattern elements that have a topic child and are the first meeting_pattern in their block so you get Topics A, B and D. If you just want the first one with a topic over the whole document then use parentheses, "(/meetings/meeting/meeting_pattern[topic])[1]".
If your structure was simpler, like this:

Code:

<meetings>     <meeting_pattern><topic>A</topic></meeting_pattern>
<meeting_pattern></meeting_pattern>       <meeting_pattern><topic>B</topic></meeting_pattern>
<meeting_pattern><topic>C</topic></meeting_pattern>    <meeting_pattern><topic>D</topic></meeting_pattern>
<meeting_pattern></meeting_pattern>
</meetings>

then "/meetings/meeting_pattern[topic][1]" and "(/meetings/meeting_pattern[topic])[1]" would both give Topic A.
I have used the short form of "[1]" which equals "[position() = 1]" in all these examples.

Joe (MVP - xml)

armmarti · November 19th, 2003, 11:30 AM

It's ok, but in that case you'll be able to process only that "meeting_pattern" (which is the first "meeting_pattern" having a "topic" child in document order). So for generality, you'll need this (note that you missed quotation in <xsl:apply-templates select="meeting_pattern" mode ="topic"/>):

Code:

<other stuff>
<xsl:variable name="selected-pattern" select="(//meeting_pattern[topic])[1]"/>
<xsl:apply-templates select="meeting_pattern" mode ="topic"/>
<xsl:template match="meeting_pattern" mode="topic">



   <xsl:if test="generate-id() = generate-id($selected-pattern)">
      <xsl:value-of select="topic"/>
   </xsl:if> 
</xsl:template>

Regards,
Armen

pdamer · November 19th, 2003, 11:30 AM

My document is like your first example but that is actually the behavior that I need so one topic per <meeting> is perfect.

Very nice explanation, Thanks!
-Paul