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RE: @context everywhere; applies to ref and value separately, or applies before ref, then ref applies to value?

From: Klotz, Leigh <Leigh.Klotz@xerox.com>
Date: Fri, 18 Jun 2010 11:21:57 -0700
Message-ID: <E254B0A7E0268949ABFE5EA97B7D0CF40AFA7D3F@USA7061MS01.na.xerox.net>
To: "John Boyer" <boyerj@ca.ibm.com>
Cc: <public-forms@w3.org>
Thank you, John.  That's great news.  I had gotten confused and thought context was an XForms 1.2 feature; so @context everywhere is, but context() isn't.
I'll note this in the wikipage on @context everywhere.
 
I have another question about context(), though, and it would have applied equally to my misunderstood @context:
 
#fn-context says that it applies to "context node of the nearest ancestor element".  So, that means it isn't useful for child elemements which allow evaluation of xpath expressions for what would otherwise be static attribute values.
For example, output/mediatype/@value cannot use context().
 
Leigh.
 
   
________________________________

From: John Boyer [mailto:boyerj@ca.ibm.com] 
Sent: Friday, June 18, 2010 7:19 AM
To: Klotz, Leigh
Cc: public-forms@w3.org
Subject: Re: @context everywhere; applies to ref and value separately, or applies before ref, then ref applies to value?



Hi Leigh, 

First, to clarify, you're trying to get the value attr in setvalue to evaluate "name" as the name of the hotel that is both good and cheap, i.e. the value expression evaluates relative to the repeat item node rather than the result of the ref in setvalue. 

While the ref sets the starting node of the value, the repeat item node happens to be the "inscope evaluation context node" of the setvalue action, which sets the starting node of the ref. 

Therefore, no, the context attribute will not help you with resetting the evaluation node for the value attr.  The context attribute allows override of the inscope evaluation context of the element containing the context attribute, so it would only help you to set a context for the ref of the setvalue. 

Unfortunately, Mark's blog post is also incorrect, and you are correct, that using the current() function does not work.  Later in Mark's post, he does acknowledge that. 

The actual fix to the problem is the context() function [1], and you're hitting on the exact reason it was added. 

[1] http://www.w3.org/TR/xforms11/#fn-context <http://www.w3.org/TR/xforms11/#fn-context>  

In your markup, use this: 
<setvalue ev:event="DOMActivate"  
ref="instance('home')/hang/your/hat" value="context()/name" />

If Mark's post contained context() where it currently contains current(), then his blog post would work without having to resort to the index() function: 

<xf:setvalue bind="testBind" value="context()/VO_ID" /> 

Finally, note that context() is one of the harder functions to implement, so you may have to file an issue with your flavourite XForms implementer if the above doesn't work.  And meanwhile, could you explain further what breaks when you use the alternative method of the index() function to solve this problem in an inner repeat?  Offhand, the only reason I can think of why it wouldn't work is that the harder part of implementing the index() function has not been done properly, which would mean another issue for your flavourite XForms implementer. 

Cheers, 
John M. Boyer, Ph.D.
IBM Distinguished Engineer, Interactive Web Applications and Documents 
IBM Lotus Forms Architect
Workplace, Portal and Collaboration Software
IBM Canada Software Lab, Victoria
E-Mail: boyerj@ca.ibm.com  

Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer <http://www.ibm.com/developerworks/blogs/page/JohnBoyer> 
Blog RSS feed: http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw <http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw> 





From: 	"Leigh L. Klotz, Jr." <Leigh.Klotz@Xerox.com> 
To: 	public-forms@w3.org 
Date: 	06/17/2010 11:37 PM 
Subject: 	@context everywhere; applies to ref and value separately, or applies  before ref, then ref applies to value?

________________________________




When we add @context to actions [1], would this work to deal with the 
lost repeat context in setvalue problem?

<repeat nodeset="instance('directory')/hotels/hotel[@good='yes' and 
@cheap='yes']">
<trigger>
<label>Book <output ref="name" /></label>
<setvalue ev:event="DOMActivate" context="." 
ref="instance('home')/hang/your/hat" value="name" />
</trigger>
</repeat>

(You can work around this loss of context with index(), but not in the 
case of nested repeats.)

Interestingly, Mark Birbeck suggests [2] that current() solves this 
problem, but my understanding was that
<setvalue ref="instance('home')/hang/your/hat" value="current()/name" />
was the same as
<setvalue ref="instance('home')/hang/your/hat" value="./name" />
and current() would be useful only inside predicates.

Am I wrong on this count?

[1] http://www.w3.org/MarkUp/Forms/wiki/@context_everywhere <http://www.w3.org/MarkUp/Forms/wiki/@context_everywhere> 
[2] http://www.formsplayer.com/node/200 <http://www.formsplayer.com/node/200> 

Leigh.
Received on Friday, 18 June 2010 18:22:43 UTC

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