Updating the model via AJAX

Question

Victor,
I find Tor's and Greg M's bpcatalog documents describing AJAX and JSF useful. However they do not address 'updates'.
Updating the model via an AJAX request that is handled by the JSF framework as suggested by bccatalog examples is a challenge.
I am not sure if it is best to use the "Update Model" phase of the life cycle or just cheat and put he update code in the tags render response phase. Also, it appears that the "update model Phase" may not be included in the lifecycle as the ajax request is not really a JSF "postback".
Does anyone know what tradeoff result in doing an update in the Render Response Phase?
Cheers,
Godfrey

Answer 1

I've tried updating the model using AJAX and a RenderPhaseListener, but never succeeded. I have a simple CRUD form with two selectOneMenu components, some text boxes, and a submit button. When a selection is made in the first select list, an AJAX call is made that populates the second select list. Once that happens, the second select list contains a different list of <f:selectItems> in the DOM than it does in the underlying component model. If the array of SelectItems that are used to populate the second select list is in a managed bean, when the form is submitted, the second select list fails validation (Validation Failed: Not a Valid Value) because the selected item exists in the DOM, but not in the SelectItem array in the managed bean. To work around this, I placed the SelectItem array in the session, instead of in the managed bean. When the AJAX call is made, the backend Java code updates the SelectItem array in the session. This prevents the model and the DOM from getting out of synch. I hate putting anything in the session, because sessions tend to die, but this is the best workaround I could come up with. I'm open for any better solutions. Oh, by the way, if I use AJAX enabled select lists on a JSF page in a JSF 1.0 web app, the Invoke Application phase is mysteriously skipped when the form is submitted, which prevents the form contents from being saved. If I use JSF 1.1_01, the form saves like a charm. You gotta love being on the bleeding edge.