JPQL query- order by nested field

Question

Given a class OP

public class OP {
  String name;
  int rank;
}

and a class D

public class D {
  OP parameter; 
}

How should be the query written in JPQL that lists the instances of D class ordered by rank field of OP class. Instances having null references to OP objects must listed at the end.

Answer 1

After some tests I managed to get things work. This is how I have implemented it with Spring Repository :

@Repository
public interface DRepository extends CrudRepository<D, Long> {

    @Query("select d from D d left outer join d.parameter op order by op.rank desc")
    List<D> getDs();

}

Notice the left outer join to include D instances with null parameter field and the desc after the order by clause to force instances with null OP to the end of the list.