How to control the processing of the request?

Question

I have something like this:
<h:inputText value="#{sessionController.currentRowData.settlementId}"/>
<h:inputText value="#{sessionController.currentRowData.remark}"/>
<h:inputText value="#{sessionController.currentRowData.fromDate}">
     <f:convertDateTime pattern="yyyy-MM-dd"/>
</h:inputText>
The currentRowData object is the currently selected row of a data model.
Problem is, the model is updated with the value of the components whenever the form is submitted,
and regardless of whether the value of the components has changed or not.
(Actually, the behaviour depends on the type of the property, as ie. Date is treated differently from String or int.)
This causes unwanted changes to the model, and, if a new row is selected, it will at once
be updated with the values of the previous row (from the current state of the components).
I want the above components to update the model only if the user wants to, ie. only if a
specific command button is pressed.
How to control this?
Let a PhaseListener check the request, and do renderResponse on the FacesContext if
the "selectRow" request is found in the request parameter map?
This is not very elegant, and it does not seem to work either. If setting PhaseId to APPLY_REQUEST_VALUES, the action itself (selecting row)
will not be executed, and if using UPDATE_MODEL_VALUES, the value of the components is set from the request (even if unchanged), and not updated according the the new data in the model (the rendered values does not reflect the values of the properties of the object the components are bound to)
Another solution might be to let the "disabled"-attribute of the inputText tags be dependent on whether
a specific "edit"-button has been pressed (disabled inputText tags are rendered correctly after a row change).
But a better solution would to have the ability to control the behaviour, something like
"for these components, no updating of state should be done unless the condition c is true"
(I'm not sure what condition this could be, though).
Whatever solution I may end up with, the real problem seems to be that the state (and hence the model)
is updated from the request also in the case where the value in the request is the same as the current value of the component.
Or maybe there is something I have missed here?
erik

Answer 1

This one is a tricky problem - a side-effect of JSF doing a lot of things automatically is that sometimes it does too much.
I don't have a great solution, but here's a couple of ideas:
(1) Try using multiple <h:form>s on your page (not nested one inside the other, but separate). Data will only get updated in the form that contains the button that got pressed.
(2) Use an intermediate model layer, and discard updates as appropriate.
Neither of these are beautiful solutions - the second is way ugly - but they might help. Long-range, I'd love to see something like "subforms" supported in JSF that can provide finer grained control over what gets processed (validations, model pushes, etc.) and what doesn't without resorting to the blunt hammer of multiple HTML forms.
I'm a little confused about "the model is updated with the value of the components whenever the form is submitted, and regardless of whether the value of the components has changed or not.", because JSF is checking the old value and using ".equals()" to see if its changed. Note, however, that it's not caching the old value across the request, but simply going back to the model on the subsequent request, which may (or may not) explain the behavior you're seeing.
-- Adam Winer (EG member)