AjaxFormComponentUpdatingBehavior breaking wicket 's convention ? Which alternatives then?

[Joseph Pachod]

 
hi

I was quite surprised, recently, by the AjaxFormComponentUpdatingBehavior, 
which directly updates the model. At the time it seemed pretty  odd but I moved 
on. 

then I recently read this article from Igor, Building a ListEditor form 
component 
(http://wicketinaction.com/2008/10/building-a-listeditor-form-component/comment-page-1/)
 which states "in order to be a good citizen in Wicket’s form processing" a 
component should "Implement atomic form updates – this is perhaps the most 
important  feature. If the user moves an item up or down in the list this 
change  should not be reflected in the model object until the form is  
submitted."

However, the AjaxFormComponentUpdatingBehavior completely breaks this important 
aspect, by going directly at the model. Furthermore, the javadoc doesn't 
illustrate how dangerous it is. For example, setting setDefaultFormProcessing 
on some cancel button won't work anymore. Neither does the javadoc hint at some 
ways to avoid this.

Among the way to avoid this, I currently mostly see the 
AjaxFormValidatingBehavior or writing an ad hoc form component copying his 
initial state and implementing IFormModelUpdateListener.

Thinking back on my initial issue, a Behavior which would only update the input 
of the component would have been resolved it (issue was a listview where adding 
a line would loose non submitted input on textfields). 

A such "AjaxFormComponentConvertingBehavior" is in fact easy to do, it's a copy 
of AjaxFormComponentUpdatingBehavior with a shortened onEvent: 
@Override
    protected final void onEvent(final AjaxRequestTarget target) {
        final FormComponent<?> formComponent = getFormComponent();

        if (getEvent().toLowerCase().equals("onblur") && disableFocusOnBlur()) {
            target.focusComponent(null);
        }

        try {
            formComponent.inputChanged();
            onUpdate(target);
        } catch (RuntimeException e) {
            onError(target, e);

        }
    }

 Such a behavior would resolve some of the use case currently  "wrongly" 
addressed by the AjaxFormComponentUpdatingBehavior. It could even be its parent 
class and be spoken of in its javadoc. 

What your feelings on that ?

sorry for this long post and thanks in advance for your answers (which most 
likely will show I've missed something obvious there!).

++
joseph