Re: Non-intuitive behavior from the For component

[Chris Conrad]

I think the problem here (and this is also in regards to using the  
keyProvider parameter and equals method) is I'm dealing with a list  
of objects which are 100% legitimately equal to each other.  And  
that's really what I want.  I want the For component to take a list  
of equal objects to render the page and then, during the rewind,  
update that list of objects according to their index in the list.   
When I start I have no identifying information about the list of  
objects, all I know is that I need x number of them.

To try and explain in a different way ... if you look at the Form  
section of the Quick Start guide you can see the standard pattern for  
having a user fill in a form to create a new object.  In the Quick  
Start guide it's creating a new ProjectRelease.  So, as in the  
example, in your pageBeginRender you instantiate a blank  
ProjectRelease and when the form is submitted, the fields of the  
ProjectRelease are updated according to the values in the form.  I  
want to do the same thing but instead of creating a single  
ProjectRelease, I want to create a list of ProjectReleases.

Does that help any?

--Chris

On Jan 26, 2006, at 12:36 PM, Jesse Kuhnert wrote:

Hmmm....But that only causes more confusion I'm afraid :(

Ohhhhhh....I think what you are doing sort of sounds right, but you  
still
can't expect the For component to be able to know the difference  
between all
of your objects if the equals() method on them doesn't enforce some  
sort of
uniqueness.

Have you tried playing with the "match" parameter to For? I've  
normally used
the "ListEdit" component for things like this in the past. Would  
love to
hear if "match" or some of the other parameters solve your problem.

On 1/26/06, Chris Conrad <[EMAIL PROTECTED]> wrote:

Sorry to reply twice, but I thought some code snippets might make
things clearer.  Here is what I do in my pageBeginRender:

             rsvpList = new ArrayList<Rsvp>(numberAttending);

             for (int i = 0; i < numberAttending; i++) {
                 Rsvp rsvp = new Rsvp();
                 rsvp.setId(i);
                 rsvp.setAttending(true);

                 rsvpList.add(i, rsvp);
             }

             setRsvpList(rsvpList);

My listener method looks like:

         // Reset the ids to 0
         List<Rsvp> rsvpList = getRsvpList();
         for (Rsvp rsvp : rsvpList) {
             rsvp.setId(0);
         }

         getRsvpData().setRsvpList(rsvpList);

And then in my HTML template I use it like this:

         <div jwcid="@For" source="ognl:rsvpList"
value="ognl:currentRsvp">
             <div jwcid="@Any" element="div"  
class="ognl:evenOdd.next">
                 <p class="floatLeft">
                     <label jwcid="@FieldLabel"
field="component:guestName">Guest's Name</label>
                     <input jwcid="guestName" size="30"/>
                 </p>

                 <p class="floatLeft">
                     <label jwcid="@FieldLabel"
field="component:meal">Meal</label>
                     <input jwcid="meal"/>
                 </p>
                 <br class="clear"/>
             </div>

The bit that bothers me is that in my pageBeginRender I need to do  
this:
                 rsvp.setId(i);

and in my listener I need to do this:

         // Reset the ids to 0
         List<Rsvp> rsvpList = getRsvpList();
         for (Rsvp rsvp : rsvpList) {
             rsvp.setId(0);
         }

I need to do that exclusively so that the For component can update
the List correctly.

Hopefully that makes things a little clearer.

--Chris

On Jan 26, 2006, at 11:58 AM, Jesse Kuhnert wrote:

Hmmm. .

I do these sort of things a lot, esp. with hibernate. I've found
the For
component to incredibly useful, but maybe the identification of
objects part
could be made more clear?

I think the PropertySelectionModel problem could be solved if you
used the
"BeanPropertySelectionModel"  class found in
http://tacos.sourceforge.netinstead. It makes turning a list of
hibernate objects into the selection
model a one-line argument.

Let me know if you try that and still find problems.

On 1/26/06, Chris Conrad <[EMAIL PROTECTED]> wrote:

Hello everyone,

I'm working a tiny little RSVP for a friend.  While doing so I  
found,
what seems to me at least, a very non-intuitive result from the For
component.  Basically the behavior I want is:

1. The user navigates to the RSVP page and is provided a drop down
box to select the number of people who will be attending the event.

2. The user is given a list of text entry boxes (to enter the  
name of
the guest) and drop downs (to select the meal the guest wants).

1 was simple to accomplish though having to create a
PropertySelectionModel is kinda a pain for something this simple.
Where things got hairy is 2.  Basically the code flow is: in the
listener for the form submit in #1, I grab the number of guests
attending and set that on the meal selection page.  The meal
selection page's pageBeginRender creates a List of x RSVP objects
where x is the number of guests attending.  Then the meal selection
page uses a For component to loop through the List of RSVP  
objects so
that, in the first pass everything is blank and then when the guest
submits, those RSVP objects in the List get filled in with the
details the guest entered.

Now, what actually happened is the first RSVP object in the list is
continually updated over and the others are never touched.  When
tracing through the For components code, it appears to be trying to
match the serialized object saved in the form against the ones  
in the
List to "intelligently" pick which one to update.  But since all of
the RSVP objects were the same to start with, and the For component
doesn't update it's internal mapping after updating an object, it
just ignored everything in the list after the first item.  Or, I
guess more accurately, it continually matched the first item in the
List and so it just repeatedly updated that one RSVP object. To  
work
around this, I needed to set the RSVP's id in the  
pageBeginRender to
a different value for each RSVP object and then reset them back  
to 0
just before sending them to Hibernate to persist (if I don't reset
them to 0, Hibernate things it's a detached object and ends up
updating a row instead of adding a new row).

This work around seems very much like a hack to me.  Is there a way
to make the For component do the right thing (i.e. actually iterate
over the array when rewinding instead of assuming it knows what  
it's
doing)? I did try playing with the match parameter and that
completely breaks everything, none of the objects in the List get
updated.  It seems that my use case isn't so terribly strange  
that it
would be this difficult to accomplish in Tapestry.

Thanks,
--Chris

------------------------------------------------------------------- 
--
To unsubscribe, e-mail: tapestry-user- 
[EMAIL PROTECTED]
For additional commands, e-mail: tapestry-user-
[EMAIL PROTECTED]




---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: tapestry-user- 
[EMAIL PROTECTED]




---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]