EclipseLink ManyToOne - CriteriaBuilder Generated Query is Wrong

I have an Entity with a ManyToOne Relationship to the Primary Key of another entity. When I create a query that references this Foreign Key eclipseLink always creates a join instead of simply accessing the Foreign Key.

I have created a highly simplified example to show my issue:

@Entity
public class House {
  @Id
  @Column(name = "H_ID")
  private long id;

  @Column(name = "NAME")
  private String name;

  @ManyToOne
  @JoinColumn(name = "G_ID")
  private Garage garage;
}

@Entity
public class Garage{
  @Id
  @Column(name = "G_ID")
  private long id;

  @Column(name = "SPACE")
  private Integer space;
}

I created a query that should return all houses that either have no garage or have a garage with G_ID = 0 using the CriteriaBuilder.

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<House> query = cb.createQuery(House.class);
Root<House> houseRoot = query.from(House.class);
Path<Long> garageId = houseRoot.get(House_.garage).get(Garage_.id);
query.where(cb.or(cb.equal(garageId , 0), cb.isNull(garageId)));
TypedQuery<House> typedQuery = entityManager.createQuery(query);
List<House> houses = typedQuery.getResultList();

The generated query is:

SELECT h.NAME, h.G_ID FROM HOUSE h, GARAGE g WHERE (((h.G_ID= 0) OR (g.G_ID IS NULL)) AND (g.G_ID = h.G_ID));

I don't understand why

The or condition first references table HOUSE and then GARAGE (instead of HOUSE)
The join is created in the first place.

The correct query should look like this in my understanding:

SELECT h.NAME, h.G_ID FROM HOUSE h WHERE (((h.G_ID= 0) OR (h.G_ID IS NULL));

Or if a join is made it should take into account that the ManyToOne relationship is nullable and therefore do a LEFT OUTER JOIN.

SELECT h.NAME, h.G_ID FROM HOUSE h LEFT OUTER JOIN GARAGE g ON (h.G_ID = g.G_ID ) WHERE (h.G_ID = 0) OR (g.G_ID IS NULL);

(Note both these queries would work correctly in my more complicated setup. I also get the same error when only wanting to retrieve all houses that have no garage.)

How can I achieve this (while still using the CriteriaBuilder and ideally not having to change the DB Model)?

(Please let me know any additional information that might be required, I'm very new to this topic and came across this issue while migrating an existing application.)

-- edit -- I have found a solution to my problem that will result in slightly different behaviour (but in my application that part of the code I had to migrate didn't make much sense in the first place). Instead of using

Path<Long> garageId = houseRoot.get(House_.garage).get(Garage_.id);

I use

Path<Garage> garage = houseRoot.get(House_.garage);

And then as expected table Garage isn't joined anymore. (I assume the code previously must have been some kind of hack to get the desired behaviour from openJPA)

Solution

I don't understand why

The or condition first references table HOUSE and then GARAGE (instead of HOUSE)

I believe this is implementation specific; in any case, it shouldn't have any bearing on the results.

The join is created in the first place.

By saying Path<Long> garageId = houseRoot.get(House_.garage).get(Garage_.id) you're basically telling EclipseLink: 'join Garage to House, we're gonna need it'. That you then access Garage_.id (and not, for example, Garage_.space) is inconsequential.

If you don't want the join, simply map the G_ID column one more time as a simple property: @Column(name = "G_ID", insertable = false, updatable = false) private Long garageId. Then refer to House_.garageId in your query.

Or if a join is made it should take into account that the ManyToOne relationship is nullable and therefore do a LEFT OUTER JOIN.

Path.get(...) always defaults to an INNER JOIN. If you want a different join type, use Root.join(..., JoinType.LEFT), i. e. houseRoot.join(House_.garage, JoinType.LEFT).get(Garage_.id).