New "initId" attribute

[Sylvain Vieujot <sv...@apache.org>]

The new attribute

The id can't be initialized with an EL expression, and we can't allow it
if we want to keep all chances to pass the TCK tests.
But the possibility to initialize a component's id with a runtime
computed value is quite crucial (see bellow).

So I propose to add a new attribute for the x: components that allow the
id to be initialized with a VB expression like :
<x:myFacesComponent initId="CMP_#{rowVar.id}" .../>

This would set the component's id on creation. Once set, the id is never
changed.


Why we need it

In dataTables, you sometime need to set the component's ids.
But as the ids have to be unique, if you can use only constants, you
can't set the ids.

Here is an example where this is highly needed :
A webmail application displays the inbox with emails received (last
received first).
On each inbox's row displays the email subject and a checkbox to be able
to delete the email right from the inbox view.
At the bottom of the page is an update bottom to show the updated inbox,
and to delete checked for delete emails.
If you check the email on row 3 for deletion and if before you press the
update button, you receive a new email, then when your request is
submitted email #3 is former email #2.
As the checkbox id's are based on the row number, you end-up
unintentionally deleting the wrong email.
The best fix to this problem is to set the checkboxes' ids to a unique
string depending upon the email, like : 
<x:selectBooleanCheckbox initId="Delete_#{email.primaryKey}_CB"
value="#{inboxFace.removeEmailUnid[email.unid]}"/>
That way, application has no unexpected behavior.

Craig suggested an alternative approach to this particular problem,
involving a hidden field (see bellow).
I didn't find how to use this, and I'm not sure it's really feasible.
Anyway, even if it turns out it could work, it would be a tricky
solution to a commonly found problem.
Using this initId attribute would be a more elegant and general solution
for this kind of problems.

Any thought ?

Sylvain.

-------- Forwarded Message --------
From: Sylvain Vieujot <sv...@apache.org>
Reply-To: MyFaces Discussion <us...@myfaces.apache.org>
To: craigmcc@apache.org
Cc: martin@marinschek.com, MyFaces Discussion <us...@myfaces.apache.org>
Subject: Re: ForcedID is not working
Date: Mon, 13 Jun 2005 17:51:20 -0400

Hello Craig,

I understand your concern about the TCK tests.
But I don't see how to use the hidden field you suggest.

In the table, I have a checkbox for each email, and each email whose
check box is checked should be deleted.
I had a similar problem with a list of images whose titles could be
edited directly in the table.
I don't see how with a hidden field (or hidden fields) you can fix the
problem.

Could you give me a clue ?

Thanks,

Sylvain.

On Mon, 2005-06-13 at 09:45 -0700, Craig McClanahan wrote: 

> On 6/13/05, Sylvain Vieujot <sv...@apache.org> wrote:
> >  I'm just getting in a problem because the id doesn't support EL right now.
> >  
> >  I have a table that displays a webmail inbox.
> >  On each row, I have a delete this email checkbox.
> >  
> >  It works fine except that it you receive a new email before you submit your
> > form, the wrong email is deleted, as the checkbox's name is based on the row
> > number, and the emails have all been shifted one row down.
> >  
> >  The only solution I've found to this (and other similar) problem(s) is to
> > use the email's id in the checkbox's id :
> >  <x:selectBooleanCheckbox id="Delete_#{email.unid}_CB"
> > value="#{inboxFace.removeEmailUnid[email.unid]}"/>
> >  
> >  This doesn't work right now, but I think the only solution to this problem
> > IS TO ALLOW EL in id attributes.
> >  
> >  The 1.1 & 1.2PR Spec. section 3.1.4 says that "all properties other than id
> > and parent, are value binding enabled".
> >  But we could partialy enable it. I mean use the value binding the first
> > time the component's id is used, and then freeze this value.
> >  
> >  Any thoughts ?
> > 
> 
> If the TCK inludes tests to verify that "id" is *not* value binding
> enabled (which wouldn't surprise me since it is a stated spec
> requirement), then this solution would just have to be undone again in
> order to pass the tests.
> 
> An alternative appropach would be to include a hidden field in one of
> the columns that contains the information you need to identify the
> correct model data (the message identifier for a mailbox screen, for
> example).  As decoding occurs and events are fired, the value of this
> hidden field (along with all the others on the current row) will have
> been restored to what it was, so that if the checkbox is checked you
> can go find the relevant message to update or delete.
> 
> Craig
> 
> >  
> >  On Tue, 2005-06-07 at 22:01 +0200, Martin Marinschek wrote: 
> >  rational explanation:
> > 
> > a value in a value-binding can change
> > 
> > - the unique id must stay the same over the whole lifetime of a view,
> > if not, where will you post the value of an input to if its id has
> > changed?
> > 
> > regards,
> > 
> > Martin
> > 
> > On 6/7/05, Mike Burati <mb...@bowstreet.com> wrote:
> > > 
> > > > The #{}-expression isn't evaluated in the id-attribute, why not???
> > > 
> > > The #{} expression support for Value Binding is a runtime/request-time
> > > facility.
> > > 
> > > The id attributes are used as component identifiers, by JSF, to build up
> > > a component tree with unique identifiers per naming container.
> > > 
> > > See Section 3.1 of the JSF1.1 specification for more information on
> > > component identifiers and value binding. Per the spec, the id and
> > > parent are the only attributes of the UI components not enabled for
> > > value binding...
> > > 
> > > 
> > > **********************************
> > > Michael Burati
> > > Senior Software Engineer
> > > Bowstreet
> > > 200 Ames Pond Drive
> > > Tewksbury, MA 01876
> > > T 978-863-1512
> > > F 978-863-1555
> > > www.bowstreet.com
> > > 
> > > Get the latest information on Bowstreet's events and web seminars.
> > > 
> > > 
> > > 
> > > -----Original Message-----
> > > From: hendrik-neumann@web.de [mailto:hendrik-neumann@web.de]
> > > Sent: Tuesday, June 07, 2005 3:28 PM
> > > To: MyFaces Discussion
> > > Subject: Re: ForcedID is not working
> > > 
> > > *lol*, thanks I'll give it a try ;)
> > > 
> > > By the way: why can't I do something like <tag
> > > id="category-#{node.identifier}" />
> > > 
> > > The #{}-expression isn't evaluated in the id-attribute, why not???
> > > 
> > > Am Dienstag, 7. Juni 2005 20:03 schrieb Korhonen, Kalle:
> > > > true to
> > > > guide MyFaces to leave the id as is, to whatever you've set it to.
> > > > Granted, the name is misleading IMHO as well.
> > >
> > 
> >