Understanding context node in templates

Birger · August 29th, 2004, 10:28 AM

Could someone please help me understanding the TEMPLATE MATCH. This puzzles me:

xml:

<r>
  <order>
    <item>First Item</item>
  </order>
  <neworder>
    <item>Second Item</item>
  </neworder>
</r>

-----------

Using this template:

<xsl:template match="/r/neworder">
  <xsl:value-of select="item"/>
</xsl:template>

..gives me both the order and neworder values, whereas this one:

<xsl:template match="/">
  <xsl:value-of select="r/neworder/item"/>
</xsl:template>

..gives me what I expected.

Setting the context node to r/neworder, I would expect the template to disregard the order node.

My Wrox book states: "..that whatever the template uses for its match attribute becomes the context node for that template. This means that all XPath expressions within the template are relative to that node."

So, where's my understanding failing?

joefawcett · August 30th, 2004, 10:57 AM

Your first template is not matching the other items. The default templates are being invoked and leading to the results you see. To prove this try adding an extra line and you'll see the position is only next to neworder/items:

Code:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/r/neworder">
    <xsl:value-of select="position()"/><xsl:value-of select="item"/>
  </xsl:template>
</xsl:stylesheet>

For an explanation of default template see Michael Kay's Wrox books on XSLT or follow http://www.dpawson.co.uk/xsl/sect2/defaultrule.html

--

Joe (Co-author Beginning XML, 3rd edition)

Birger · August 30th, 2004, 12:07 PM

Hi Joe! - and thanks. I understand the concept of default templates, or rather why they're invoked. It's just that I can't get into my head, what the difference is in the two match and select examples I wrote. Somehow they seem to be equal to me, only split up in two different ways. I guess thats what's bothering me a lot.

If I start off with a <xsl:template match="/"> and an <apply-template select="/r/neworder"/> I've no problem with the following <xsl:template match="r/neworder"> and then the .. select="item"> part.

It looks as if I can only invoke a 'template match' using an apply template statement. And I don't think that's the case!? I hope I'm making my self clear.

joefawcett · August 31st, 2004, 04:21 AM

Well in the first example the default templates cause the document root to be matched and processed which recursively calls apply-templates on all children and outputs text as it goes along. You can add the empty template

Code:

<xsl:template match="*"/>

if you want to supress unawanted output.
Another good way if to step through the transform in an XSLT debugger if you have one, XMLSpy has one, I think, as does VS.Net 2005.

--

Joe (Co-author Beginning XML, 3rd edition)