[hibernate-dev] Queries executed with bidirectional @OneToOnes

Steve Ebersole steve at hibernate.org
Wed Feb 29 13:50:33 EST 2012

How are you loading these?  Using Query#iterate I assume?

On Wed 29 Feb 2012 11:21:36 AM CST, Guillaume Smet wrote:
> Hi,
> It's not something new as we checked that it was already the case with
> Hibernate 3.6 but we just hit an annoying problem with @OneToOne
> annotation if the relation is bidirectional.
> Simplified example:
> class A {
>          @OneToOne(cascade = CascadeType.ALL, orphanRemoval = true)
> 	private B b;
> }
> class B {
>          @OneToOne(mappedBy = "b")
> 	private A a;
> }
> If we insert 1 object in each table and we try to list the objects of
> A, the following queries are executed:
> 1. select a0_.id as id55_, a0_.b_id as b2_55_ from A a0_
> 2. select b0_.id as id54_1_, a1_.id as id55_0_, a1_.b_id as b2_55_0_
> from B b0_ left outer join A a1_ on b0_.id=a1_.b_id where b0_.id=1
> 3. select a0_.id as id55_1_, a0_.b_id as b2_55_1_, b1_.id as id54_0_
> from A a0_ left outer join B b1_ on a0_.b_id=b1_.id where a0_.b_id=1
> I don't understand the need for the third query. And this query
> quickly becomes a problem as it's executed for each EAGER @OneToOne
> relationship of A.
> In our application, we have a lot of @OneToOne relationships on an
> entity and a variant of the third query (which is big as the entity is
> big and the third query tries to populate all the EAGER relations) is
> executed for each @OneToOne of the base entity.
> I can provide more information if needed. I don't know if it's a
> limitation or a bug, that's why I haven't created a JIRA issue yet but
> I find this behaviour really suboptimal.
> As a temporary workaround, we made the @OneToOne relations
> unidirectional which makes our application usable again.
> Any pointers on where the problem could be or a confirmation that it's
> something expected?
> Thanks.

steve at hibernate.org

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