JPQL Query on Type

timfulmer · **Joined:** Thu Nov 09, 2006 9:42 pm **Posts:** 13

Hello,

We recently ran into a situation where it would be nice to add a subclass of an entity to the model and query an entity based on what type an attribute is. The entities might look something like this:

Code:

@Entity class Root{
  @Id Long id;
  @ManyToOne Parent parent;
}
@Entity @Inheritance( strategy= SINGLE_TABLE) class Parent{
  @Id Long id;
}
@Entity class Child extends Parent{
  @Id Long id;
  @Basic String additionalAttribute;
}

Now I would like to select all Root instances where Root.parent is a Parent and not a Child. JPQL does not seem to support this, though a strongly typed object query language would seem to imply this is possible. If this were Java code it would be something like !(root.parent instanceof Child).

--
Tim

cbredesen · **Posted:** Thu Jul 12, 2007 9:39 pm

http://www.hibernate.org/hib_docs/entit ... yhql-where

Quote:

Likewise, the special property 'class' accesses the discriminator value of an instance in the case of polymorphic persistence. A Java class name embedded in the where clause will be translated to its discriminator value. Once again, this is specific to HQL.

Code:

select cat from Cat cat where cat.class = DomesticCat

Hope this helps!