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

From: John Boyer <boyerj@ca.ibm.com>
Date: Fri, 18 Jun 2010 07:18:37 -0700
To: "Leigh L. Klotz, Jr." <Leigh.Klotz@Xerox.com>
Cc: public-forms@w3.org
Message-ID: <OFB1640BA1.DD0E2FC0-ON88257746.004C6EED-88257746.004E9BCF@ca.ibm.com>
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

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
Blog RSS feed: 
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
[2] http://www.formsplayer.com/node/200

Leigh.
Received on Friday, 18 June 2010 14:19:11 UTC

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