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Re: xslt trouble with xsl:if

 
 
Peter Flynn
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      04-20-2008
z1 wrote:
> hi-
>
> i am fooling around with soap and weather templates.
> for some reason either this if or select is failing.
> i am very new to xml and found this code at another site.
> i can show you the xml and then the xslt sample code that is not matching.
> please look and if it jumps right off the page give me a tip on why it didnt
> select the data.
> i think for most xslt people this will be easy. i want the if to work if it
> is null because
> the weather service may return null for an attribute.
>
> from the government weather service:
> <weather time-layout="k-p24h-n5-1">
> <name>Weather Type, Coverage, and Intensity</name>
> <weather-conditions weather-summary="Increasing Clouds"/>
> <weather-conditions weather-summary="Partly Cloudy"/>
> <weather-conditions weather-summary="Partly Cloudy"/>
> <weather-conditions weather-summary="Mostly Sunny"/>
> <weather-conditions weather-summary="Chance Rain Showers">
> <value coverage="chance" intensity="light" weather-type="rain
> showers" qualifier="none"/>
> </weather-conditions>
> </weather>
>
>
> from a sample template i found:
> <xsl:template name="weather">
> <xslaram name="position" />
> <xsl:if
> test="/dwml/data/parameters/weather/weather-conditions[position()=$position]/@weather-summary
> !=''">


Depending on how the incoming data is handled (parsed as well-formed
only, or validated), position() may evaluate to one of two things:

a) what you intuitively expect (if you're used to normal text document
markup (HTML, DocBook, TEI, etc): the numeric position of the
weather-conditions *element node* among its siblings (eg for
@weather-summary='Partly Cloudy' this would be "2" and "3");

b) what you don't expect (unless you came to XML via the "data-only"
route): the numeric position of the matching node among *all* types of
siblings, including the "name" element and the (otherwise irrelevant)
white-space between the weather-conditions elements (eg for
@weather-summary='Partly Cloudy' this would be "6" and "8").

I'm unclear why it would want to identify the weather-conditions element
by position anyway.

The reliable way of matching location-among-siblings is to use
[count(preceding-sibling::weather-conditions)+1=$position]

> <xsl:value-of
> select="/dwml/data/parameters/weather/weather-conditions[position()=$position]/@weather-summary"/>
> </xsl:if>
> </xsl:template>
>
> other parts of the templates are generating output (not formatted yet
> though)
> assuming that the path is correct and it looks like it is, why wont this
> match?


Use xsl-message and xsl:value-of to output the actual value of $position
to the console during execution so you can debug it.

> @weather-summary is the attribute that has a value associated with it that
> is not null.
> the path from the root looks ok....


You haven't shown us the whole document, so we'll take it on trust that
there is a containing structure reflecting /dwml/data/parameters

> i want to get into learning a little bit more about xml and xslt.
> i have a book on it and am currently studing a css book too.
> i like the fact that when i combine all the templates with html i can have
> it output
> the results formatted. i need to get better at the xslt processing.


Dave Pawson's excellent XSL FAQ (http://www.dpawson.co.uk/xsl/), and
Mulberry's XSL-LIST mailing list
(http://www.mulberrytech.com/xsl/xsl-list/index.html) are your friends.

///Peter
--
XML FAQ: http://xml.silmaril.ie/
 
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