[hibernate-dev] Typing Help with JPA 2.1 impl

[Steve Ebersole]

I realize I could split Join and Fetch into different hierarchies.  
That is what I want to try to avoid though...

On Wed 13 Jun 2012 02:55:03 PM CDT, Steve Ebersole wrote:
> I need some help with generic types in the JPA 2.1 API, specifically
> with regard to the new Join#on and Fetch#on methods. We ultimately
> unify those 2 interface hierarchies into a single hierarchy in out
> code using org.hibernate.ejb.criteria.JoinImplementor which extends
> from both Join and Fetch.
>
> The problem I am facing is in the return types. So, Join defines:
> public interface Join<Z,X> {
> public Join<Z,X> on(...);
> ...
> }
>
> Fetch defines:
> public interface Fetch<Z,X> {
> public Fetch<Z,X> on(...);
> ...
> }
>
>
> public interface JoinImplementor<Z,X>
> extends Join<Z,X>, Fetch<Z,X>, FromImplementor<Z,X> {
> ...
> }
>
> The compiler does not at all like JoinImplementor as is, so I have to
> override the method:
>
> public interface JoinImplementor<Z,X>
> extends Join<Z,X>, Fetch<Z,X>, FromImplementor<Z,X> {
> public JoinImplementor<Z,X> on(...);
> ...
> }
>
> which should be fine as it is simple return type clarification. And
> actually that definition compiles fine.
>
> However, JPA also defines a whole hierarchy from Join such as.
> CollectionJoin, ListJoin, etc. So Hibernate has for example:
>
> public interface CollectionJoinImplementor<Z,X> extends
> JoinImplementor<Z,X>, CollectionJoin<Z,X> {
> @Override
> public CollectionJoinImplementor<Z, X> on(...);
> ...
> }
>
> The IDE is fine with this type signature, however trying to compile
> this leads to the following error:
>
> types org.hibernate.ejb.criteria.JoinImplementor<Z,X> and
> org.hibernate.ejb.criteria.JoinImplementor<Z,X> are incompatible; both
> define on(javax.persistence.criteria.Predicate[]), but with unrelated
> return types
>
> I have no idea what I need to do here. Can anyone see the solution?
>
>

--
steve at hibernate.org
http://hibernate.org