RE: [xsl] Avoiding multiple "apply-templates" by creating one variable for the clauses. Is it possible?

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Hi,

Another approach altogether is to "push" the logic through templates:

<xsl:templates select="//blog"/>

... and then ...

<xsl:template match="blog[$AuthorId][not(author_id=$AuthorId)]" 
priority="2.1"/>

<xsl:template match="blog[$CategoryId][not(category_id=$CategoryId)]" 
priority="2.2"/>

<xsl:template match="blog">... process any blogs that fall through 
...</xsl:template>

Note:

1. I've used the long logic here (not Ken's more succinct version), 
since in the world I work in, articles can have multiple authors and 
categories. (Dunno about your blogs.)

2. The explicit priority settings are to guard against multiple 
templates matching.

3. The approach only works if $AuthorId and $CategoryId are globally 
scoped. (And in 2.0 where you can use them in matches.)

4. In general, opinions vary on whether this is more or less legible 
and maintainable.

Cheers,
Wendell

At 01:18 PM 8/20/2009, Mike wrote:
> > >
> > >       <xsl:apply-templates select="//blog
> > >                            [not($AuthorId) or (author_id = $AuthorId)]
> > >                            [not($CategoryId) or (category_id =
> $CategoryId)]
> > >                            "/>
> >
> > I guess I'll finally drop in and add another suggestion since
> > I've been waiting for one of my XSLT students to bring it up
> > but I don't see any of them doing so.
> >
> > If you are looking for compactness, I believe the above
> > expression can be reduced to the following in both XSLT 1.0
> > and XSLT 2.0:
> >
> >        <xsl:apply-templates select="//blog
> >                             [not($AuthorId != author_id)]
> >                             [not($CategoryId != $CategoryId)]
> >                             "/>
> >
>
> I'm not convinced about this equivalence. If $AuthorId is "Mike", and
> author_id is an empty sequence, then
>
>  (a)  not($AuthorId) or (author_id = $AuthorId)  ==>  false
>
>  (b)  not($AuthorId != author_id)  ==>  true
>
> So if the optimizer does this conversion for you, it's wrong!
>
> But it's probably safe if author_id will always be a singleton node-set.





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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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