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
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