Hibernate/JPA: Is it possible to retrieve heterogeneous entities in a single query?

Question

I have 2 entities: EntityA and EntityB.

They are unrelated, and I cannot put them in a Inheritance tree for some restrictions out of the scope of this question.

Answer 1

Well, I finally figured it out.

It is enought to make the entities implement a common interface (it is not even needed to declare this interface on Hibernate).

Then, a query like this can be done:

FROM my.package.CommonInterface obj
WHERE obj IN (FROM EntityA WHERE fieldA=1) OR
      obj IN (FROM EntityB WHERE fieldB='a')

This way, you retrieve a List<CommonInterface>.

Problem solved.

Answer 2

Best thing is to performs two queries.

But if you must:

You can create a POJO to retrieve them:

class EntityAandEntityB {
    EntityA a;
    EntityB b;
    long idA;
    long idB;
    int fieldA;
    String fieldB;

    public EntityAandEntityB(long idA, long IdB, int fieldA, String fieldB) {
       this.a = new EntityA(idA, fieldA);
       this.b = new EntityB(idB, fieldB);
    }
}

Then your query would be:

select new package.EntityAandEntityB(a.idA, a.fieldA, b.idB, b.fieldB) from ( 
    (select idA, fieldA from EntityA) a
UNION
    (select idB, fieldB from EntityB) b)

This is dirty and you probably must to look carefully the syntax.

Regards.