JPA Criteria Query - How to join on only a subclass of the association entity type?

Question

I'm using Spring, Hibernate and the JPA Criteria API.

Let's say I have a Vehicle class hierarchy and a Tire class. Each Vehicle can have multiple Tires.

• Vehicle -- Tanker, Motorcylce

• Tire

I want to query for small tires that are on Tankers with a capacity over 100 gallons. But the vehicle property for Tire is of type Vehicle. Only one of the Vehicle subclasses (Tanker) has the "capacity" property. How do I tell the criteria api to join ONLY on Tankers?

Thanks!

I'm sure this is has been asked/answered before, but I think I'm missing the right terminology to have a successful search.

Answer 1

Try this:

@Entity
public class Vehicle {
    @OneToMany
    private Set<Tire> tires;
}

@Entity
public class Tank extends Vehicle {
    private int gallons;
}

@Entity
public class Motorcycle extends Vehicle {
}

@Entity
public class Tire {
}

public interface VehicleRepo extends JpaRepository<Vehicle, Long> {

    @Query("select v.tires from Vehicle v where v.gallons > ?1")
    List<Tire> findByGallonsIsGreaterThan(int gallons);
}

If you need select only subclass type in JPQL query you can use this approach:

select v from Vehicle v where type(v) = Tank
select v from Vehicle v where v.class = Tank

Example and test.