View source for Issue:Conditional clause in output?

{{Issue
 |Type        = Change Request
 |Extension   = DPL
 |Version     = 1.8.6
 |Description = 
 |Status      = open
}}

== Problem ==
Hi, I want to use an conditional clause in the output. The output should be different if there is no result, one result or multiple results. Example:

This calls images in [[:Category:Test Images]]. It can later be used on category pages using category = PAGENAME. E.g. I Have disabled the Media section on Category pages cos the navigation sucks.<br>
Atm it returns a gallery where the image links to its desc page and a list of links to the pages that use that image.
*Cookie.jpg is only used on one article only.
*Bob Ross.gif is used two articles.
*Placeholder.png is not used on any page.

{{User:Subfader/Examples/Images used}}


How it works:
<pre>
{{#dpl:
|category=Test Images
|namespace=Image
|ordermethod=firstedit
|order=descending
|count=10
|resultsheader=There are %TOTALPAGES% images in this category.
|format=«gallery»\n,\n%PAGE%¦²{User:Subfader/Examples/Images used/Template¦%PAGE%}²,,\n«/gallery»
}}
</pre>
[[User:Subfader/Examples/Images used/Template|The template]] to generate the article links = 
<pre>
{{#dpl:
|debug=0
|namespace=
|imageused={{{1}}}
|count=2
|format=,[[%PAGE%]]<br>,,
}}
</pre>


'''Now the plan is:'''
*If the image is only used on page: Gallery text = Link to the page that uses the image (standard case for my usage)
*If the image is used on more than one page: Gallery text = <code><nowiki>[[:File:%PAGE%#filelinks|X pages link to this image]]</nowiki></code> (if counting the page links is expensive then "Multiple" is ok too)
*If the image is unused: Gallery text = "This image is unused."


== Reply ==
Found a solution myself :) 

{{#dpl:
|category=Test Images
|namespace=Image
|ordermethod=firstedit
|order=descending
|count=10
|resultsheader=There are %TOTALPAGES% images in this category.
|format=«gallery»\n,\n%PAGE%¦²{#ifexpr:²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² < 1
¦(This image is not used on articles.)
¦²{#ifexpr:²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² = 1
¦²{User:Subfader/Examples/Images used/Template¦%PAGE%}²
¦([[:%PAGE%#filelinks|²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² pages use this image.]])
}²}²,,\n«/gallery»
}}
It uses another template to return the number of pagelinks. So now it works like this:

[[User:Subfader/Examples/Images_used|Images used]]:
<pre>
{{#dpl:
|category=Test Images
|namespace=Image
|ordermethod=firstedit
|order=descending
|count=10
|resultsheader=There are %TOTALPAGES% images in this category.
|format=«gallery»\n,\n%PAGE%¦²{#ifexpr:²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² < 1
¦(This image is not used on articles.)
¦²{#ifexpr:²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² = 1
¦²{User:Subfader/Examples/Images used/Template¦%PAGE%}²
¦([[:%PAGE%#filelinks|²{User:Subfader/Examples/Images used/Template/Res¦%PAGE%}² pages use this image.]])
}²}²,,\n«/gallery»
}}
</pre>

which uses [[User:Subfader/Examples/Images_used/Template|Images used/Template]]:
<pre>
{{#dpl:
|debug=0
|namespace=
|imageused={{{1}}}
|count=2
|format=,[[%PAGE%]]<br>,,
}}
</pre>

which uses [[User:Subfader/Examples/Images_used/Template/Res|Images_used/Template/Res]]:
<pre>
{{#dpl:
|debug=0
|namespace=
|imageused={{{1}}}
|noresultsheader=0
|resultsheader=%TOTALPAGES%
|format=,,,
}}
</pre>

'''Could you check if this correct? Maybe there's an easier way with including only one template.'''
<br>Feel free to close this bug and add this as new example :)

== Reply ==

I understand that in yopur case the output formatting shall depend on the amount of results found. This is not covered by the "oneresultheader etc ..". So, I think, your solution is a good way to do it.

Under performance aspects one would wish to use %PAGES% within an #ifexpr in the format statement. But at the moment the %PAGES% and the %TOTALPAGES% variables are only available within header and footer. The reason is that in some rare cases a regular expression could reduce the number of result lines delivered by the SQL statement. But in most cases %PAGES% is internally known before the formatting process is started.

So one could try to make an improvement here. If you know how to make small modifications to the php source in DPLMain.php you could change this (look near line 2600 and see function "substTagParm in DPL.php near line 175 )
If we offered %PAGES% within the format statemenmt the subquery would not be needed I think ...
 
Do you want to try and let me know?

[[User:Gero|Gero]] 22:00, 5 July 2009 (UTC)