Nullable conversation scoped component

[phantasmo]

I was wondering how would one implement the following scenario in CDI.
There's a conversation scoped object of type Item that represents a currently selected item. This object is supposed to be injected at multiple point in other classes and is also referenced on a page. It is allowed to be null signifying that no item is selected at the moment.
I have no clue how to do this without outjection as conversation scoped objects are not nullable and dependent are not unique during the conversation...

[swd847]

What about this:

@ConversationScoped
public class Manager
{
   SomeObject selected;

   @Producer
   @RequestScoped
   public SomeObject produceSelected()
   { 
     return selected;
   } 
}

[phantasmo]

Wait a sec, the spec says:

If a producer method sometimes returns a null value, then the producer method must have scope @Dependent.

And in my case (using your example), SomeObject can be null. Won't this be a problem?

Thanks!

[nickarls]

I think so. The products are checked for this.

[phantasmo]

Just for the sake of future searches, I'll add that I am trying to achieve something like this:

@Scope(ScopeType.SESSION)
public class Manager
{
    @Out(required=false)
    SomeObject selected;

  //not really relevant 
   public void findSelected(int id)
   { 
     selected = em.find(SomeObject.class, id);
   } 
}

[phantasmo]

This is a fairly common scenario, could it be that there's no straightforward way of implementing it?
Maybe I'm missing something...

Anyway, I'll appreciate any shared ideas...

[nickarls]

I generally prefer returning an object, anyway, something like

public class User
{
   public static final User NONE = new User();
}

and check against that instead of null.

[phantasmo]

Well... null was defined for a reason... Things like this force you to work around the framework instead of working with it. And that's never a good sign. The more I learn the more flawed CDI looks. I genuinely hope I just didn't get it right.

Anyway, excuse my rambling Nicklas, I am grateful for your attempts to help.

[nickarls]

Generally, if the framework imposes a limitation on you, it's because it wants you to protect you from something else ;-) Of course, there may be a simple CDI:ish workaround to this that doesn't some to mind right now...