How to save 2 dependent selectOneMenu values - ajax

Question

I'm running in a little issue here regarding jsf related dropdown selection.
I have 2 dropdown selection: the first one is independent, the second one shows result depending from This is the code:
<h:panelGroup id="addressPanel">
<h:outputLabel styleClass="label" value="Provincia: " />
<h:selectOneMenu onchange="updateCombos()"
value="#{indirizzoCtrl.codiceProvincia}" >
<f:selectItem itemValue="" itemLabel=""></f:selectItem>
<f:selectItems value="#{indirizzoCtrl.allProvincia}" var="c"
itemLabel="#{c.nome}" itemValue="#{c.siglaProvincia}" />
</h:selectOneMenu>
<h:outputLabel styleClass="label" value="Comune: " />
<h:selectOneMenu
value="#{indirizzoCtrl.codiceComune}" >
<f:selectItem itemValue="" itemLabel=""></f:selectItem>
<f:selectItems value="#{indirizzoCtrl.allComuni}" var="c"
itemLabel="#{c.descrizione}" itemValue="#{c.codiceComune}" />
</h:selectOneMenu>
</h:panelGrid>
</h:panelGroup>
<p:remoteCommand name="updateCombos" update="addressPanel masterForm:msg" />
<p:commandButton styleClass="commandButton" value="Save"
actionListener="#{indirizzoCtrl.save}">
</p:commandButton>
Well, when the user save the form after selecting both the value, the managed bean indirizzoCtrl (request scoped) cannot map the value of the second dropdown back to the list, because there's no list.
In fact the #{indirizzoCtrl.allComuni} call a getter that retrieve the data from the DB only if indirizzoCtrl.codiceProvincia!=null... and that's false before the update model phase.
So the first time the getter for the list is called cannot retrieve any values, and that's bring the update model phase to fail.
How can I handle this scenario... I think it's a pretty common one, so I'm missing something here...

Answer 1

Put the bean in the view scope instead. It will live as long as you're interacting with the same view by ajax. A request scoped bean get indeed recreated on every single request, also ajax requests, so bean properties would reinitialize to their defaults.
#ManagedBean
#ViewScoped
public class IndidizzoCtrl implements Serializable {
// ...
}
See also:
How to load and display dependent h:selectOneMenu on change of a h:selectOneMenu
How to choose the right bean scope?
Unrelated to the concrete problem, I also strongly recommend to change your getter methods to not do any business job, but just return data. Do the business job in (action)listener methods instead. E.g.
<h:selectOneMenu value="#{bean.menu1item}">
<f:selectItems value="#{bean.menu1items}" />
<f:ajax listener="#{bean.updateMenu2}" render="menu2" />
</h:selectOneMenu>
<h:selectOneMenu id="menu2" value="#{bean.menu2item}">
<f:selectItems value="#{bean.menu2items}" />
</h:selectOneMenu>
with
public void updateMenu2() {
menu2items = loadItBasedOn(menu1item);
}
See also:
Why JSF calls getters multiple times