RE: Newbie question regarding $!model and getParams()

From: Rogers, Bob [mailto:[email protected]] 
>
>Hi - After several days of playing around with Maverick and Velocity I've made some
>progress but still have a few unanswered newbie type questions I'm hoping someone
>could take the time to answer.

Hi!

>Question 1 - In general, where and how are the getParams() and setParam() used?
>If I code 'this.getCtx().setParam("age", "55")'  in the 'perform()' method, do I have
>access to this in the 'transform', and more specifically, how do I reference it in
>VLT?
> 
>Is it referenced by $model.getParams()  or  $model.getParams("age")  or
>$response.getParams() .... etc.  I've tried several permutations but just can't
>figure it out.

You would reference it by $age.  For document views and transforms, params are simply set into the request attributes.  The VelocityViewServlet searches this collection to evaluate expressions.  You could probably access it as $request.getAttribute("age"), but that's annoying :-)

Note that the current CVS version of Maverick (soon to be released as v2.2) splits up the params collection into three separate collections - controller params, view params, and transform params.  This is the result of a recent thread on this list regarding redirect views.

>Question 2 - I've seen in the opt-velocity friendbook example several references to
>"$!model.xxx".  What is the bang (ie '!')  for? and why is it used?
 
This is standard Velocity syntax for "quiet" evaluation.  Normally, if there is an error evaluating $foo.bar.blah (say, the foo object doesn't have a getBar() method, or the value of getBlah() is null) then Velocity puts the "schmoo" (Velocity lingo for an unresolved expression) as-is into the body of the document.  The ! means that nothing should be printed when the evaluation fails.

Friendbook-velocity uses this to report errors.  If there is no error, we don't want "$model.error" showing up in the html.  Instead of this syntax:

#if($model.error != null)
   $model.error
#end

It is much more convenient to just do:

$!model.error

Jeff Schnitzer
[email protected]


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