NullPointerException与Hibernate FETCH JOIN

Question

I get a NullPointerException when executing the list method on a hibernate query. This is my code:

Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();

String hql = "SELECT g FROM DeviceGroup g JOIN FETCH g.devices";
Query query = session.createQuery(hql);
List<DeviceGroup> list = query.list();

session.getTransaction().commit();
session.close();

return list;

The relationship is defined like this:

Device:

@ManyToOne
@JoinColumn
private DeviceGroup deviceGroup;

DeviceGroup:

@OneToMany(mappedBy = "deviceGroup")
private Set<Device> devices;

If I leave out the fetch join, the list method succeeds, but lazy fetching results in a StackOverflowException. What am I doing wrong?

Answer 1

尝试在g.devices上使用identifier d ，

SELECT g FROM DeviceGroup g JOIN FETCH g.devices d

Answer 2

I solved the problem. I had a hashCode implementation on the entities that caused an infinite loop. It's still quite a strange behavior to throw a NullPointerException in this case...