Controlling Hibernate's generated subselect

Question

Consider the following three Hibernate entities:

public class Car {

  @OneToMany(fetch = FetchType.LAZY)
  @Fetch(FetchMode.SUBSELECT)
  private List<Wheel> wheels;

}

public class Wheel {

  @OneToOne(fetch = FetchType.LAZY)
  private Hubcap hubcap;

}

public class Hubcap {

}

Consider the following Criteria:

Criteria criteria = getSession().createCriteria(Car.class);
List<Car> cars = criteria.list();

for (Car car : cars) {
  Hibernate.initialize(car.getWheels());
}

Is there any way to control the subselect query that will be generated? Specifically I'd like to join in the subselect so that the hubcaps are also fetched when the wheels are fetched. This can of course be accomplished by changing the FetchType to EAGER, but I need something more ad hoc - on a query by query basis.

As the code is currently I'd need to generate another select to fetch the Hubcaps.

Answer 1

Yes you can do it using criteria but I don't remember how its done, just look for joins in criteria, however I would suggest using HQL rather Criteria is far more readable:

select c 
from Car c join fetch c.wheels
where ...

Answer 2

You can change the fetch type in a criteria query with the setFetchMode method.

http://docs.jboss.org/hibernate/core/3.3/reference/en/html/querycriteria.html

Answer 3

After lots of research it appears that this is impossible at this stage, at least without extending Hibernate.