On Tue, Sep 1, 2009 at 1:15 PM, Paul Sandoz (via Nabble) <
ml-user+51078-1180840285_at_n2.nabble.com<ml-user%2B51078-1180840285_at_n2.nabble.com>
> wrote:
> I will implement support for a type T, but types like T[], Collection<T>
> and Map<T, Collection<V>> are harder to resolve because it is difficulty
> creating the concrete parameterized type definitions. If anybody knows of
> any mechanism to help aid this i am all ears!
>
OK, good to know.
> Background: I was hoping to put together a generic DAO that could return
> collections of things without having to create a new resource for every
> object that I wanted DAO functionality for.
>
> We need more samples :-) or those samples could be modified f appropriate.
> Issues/patches/contributions welcome!
>
Also good to know.
I'd like to clarify my use case in case it helps, or in case by some chance
it actually *is* handled. My use case is of course absolutely brain-dead
simple for a Java EE application sitting on top of JPA.
Right now I have a generic DAO roughly like this (again, typed off the cuff
and with lots omitted for brevity):
@Stateless
public class AbstractDAO<T, P> {
@PersistenceContext(/*...*/)
private EntityManager em;
public T find(P primaryKey) {
return em.find(primaryKey);
}
}
I'd like to add a method that, for example, runs a named query and returns
the results:
public List<T> findBySomeCriteria(/* criteria don't matter for this example
*/) {
// make the appropriate named query here
return (List<T>)query.getResultList(); // or whatever the call is; can't
remember offhand
}
And I have in mind that somehow {handwave, handwave} the returned XML would
as magically as possible be correct (suppose T evaluates to Foobar):
<foobars>
<foobar>First result item</foobar>
<foobar>Second result item</foobar>
</foobars>
Now, as it happens, I have to subclass the DAO anyway for each type of
object. This is in part so that the EJB interface it's called through
correctly reflects the right type. That is, I would have to create a class:
public class FoobarDAO extends AbstractDAO<Foobar, FoobarPrimaryKeyClass> {
/* ... */ }
Is it possible that if THIS class were invoked I would get back the proper
XML from its findBySomeCriteria method?
I am sorry--really, I am--for asking such braindead questions, but they are
the first things that my colleague and I ran up against, and we didn't find
an easy entry path towards the solution in the documentation. I am totally
open to being redirected. :-)
Best,
Laird
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