Question

I am developing a skin that INCLUDEs another topic as the sidebar. I would like it to first check the current web to see if the topic exists, and then check the TWiki web to see if it exists there. Doing this will allow individual web authors to overload the left bar. Is this possible?

I looked into how the PatternSkin does this, and it seems to just include the topic from the current web. It ensures that the topic exists in the current web by automatically creating the topic with a default layout when a new web is created. If this is the route I have to take, how can I achieve this?

Environment

-- KevinCraft - 31 Mar 2006

Answer

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looking at the docco for INCLUDE I think you should be able to do

%INCLUDE{"TheMaybeTopic" warn="%INCLUDE{\"TWiki.TheDefaultTopic\"}%"}%

though my testing suggests that the warning has a limited length - so you might need to play with it a bit

-- SvenDowideit - 07 Apr 2006

You can also use the SpreadSheetPlugin to check for the existence of a topic, and based on this include one or the other topic. Untested example:

%CALC{"$IF($EXISTS(TopicOne), $NOP(%)INCLUDE{TopicOne}$NOP(%), $NOP(%)INCLUDE{TopicTwo}$NOP(%))"}%

-- PeterThoeny - 07 Apr 2006

EXIST should be EXISTS (-:

• Fixed above example. -- PeterThoeny

I was attempting to use %IF{...}% in conjunction with %CALC($EXISTS(...)}%. An interesting thing happened with the following:

• Set AVAR = %CALC{$EXIST(%WEB%.LocalIncludes)}%

Evaluating the result in %AVAR% the statement:

%IF{" $ AVAR='1'" then="dostuff"}%

-- or --

%IF{" $ AVAR='0'" then="dostuff"}%

-- fail, while --

%IF{"defined AVAR" then="dostuff"}%

works. Apparently, the %CALC{..}% is a numeric value(?).. I dunno - I tried to coerce it by prefixing with alpha (e.g., Set AVAR = A%CALC{$EXIST(%WEB%.LocalIncludes)}%), but no go.

The solution above by Peter is very doable.. Thanks!

I gotta register! (dave mansfield)

-- TWikiGuest - 02 Nov 2006

In SVN there is a plugin called FallBackPlugin that does exactly what you're asking for. I know because I proposed the use case and MeredithLesly implemented it but never published it on TWiki.org. I have tested it and it works as advertized.

-- LynnwoodBrown - 03 Nov 2006

I'm having similar problems with DynamicDoubleBracketLink

-- KeithHelfrich - 15 Jul 2007

The SpreadSheetPlugin as a bug where you need to specify a full web.topic qualifier in the $EXISTS() function. Specify the web. prefix, or upgrade to the latest SpreadSheetPlugin.

-- PeterThoeny - 15 Jul 2007