[hibernate-issues] [Hibernate-JIRA] Created: (HHH-4935) one to one(join column in right place) causes HQL eager fetch failure

[Dean Hiller (JIRA)]

one to one(join column in right place) causes HQL eager fetch failure
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                 Key: HHH-4935
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4935
             Project: Hibernate Core
          Issue Type: Bug
    Affects Versions: 3.3.2
         Environment: linux, windows, junit test with hibernate 3.3.4, 3.4 for annotations/entityManager
            Reporter: Dean Hiller


See the end of this post...

The test case and all code can be found in here....(just modified the Cat->Kitten example till it broke)....
https://forum.hibernate.org/viewtopic.php?f=1&t=1002721&p=2425506#p2425506

basic summary though is if you have 
SELECT s FROM Cat s inner join fetch s.kitten

and you redefine Cat->Kitten to be OneToOne, it works great if JoinColumn is on kitten, but if you move JoinColumn to Cat, it results in a 1+N select where the first sql got all the data needed by hibernate to fill in the Cats and their kitten.  We have a 100 page result set that is doing 1+N selects here.

ie. if you leave the join column on kitten, the following sql is 1+N then....
SELECT k FROM Kitten k inner join fetch k.cat; (ie. a more likely case since there may be Cats without kitten, but a kitten always have a cat...that is the situation we have in our object model).

so onetoone eager fetch joins only work on half the cases out there from what I can tell and you get lucky if your join column is on the right object.




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