hibernate and jpa weirdness; unexpected lazy fetching

Question

I'm using a rather old version of Hibernate (3.2.4) so it's possible this is related to that. Unfortunately the project requirements prevent me from upgrading.

I have a class Foo with many-to-one association to Bar. The association is flagged:

lazy="false" fetch="join"

Now when I do something like:

em.find(Foo.class, id);

I get the expected result: a single statement joining the FOO table with the BAR table. However, when I try something like:

em.createQuery("select f from Foo where f.id = :id")
.setParameter("id", id)
.getSingleResult();

I get the single join followed by an additional select query against BAR. The second query seems to be entirely superfluous ; all the data needed to eagerly populate an instance of Foo should have been available from the initial join. It looks roughly like this:

select f.id, f.xyz, ..., b.id, b.xyz, ... 
from foo f 
join bar b on b.id = f.bar_id 
where f.id = ?

select b.id, b.xyz, ... 
from bar b 
where b.id = ?

Any thoughts?

Answer 1

Hibernate doesn't respect fetch = "join" when executing HQL queries. From the documentation :

The fetch strategy defined in the mapping document affects:

• retrieval via get() or load()
• retrieval that happens implicitly when an association is navigated
• Criteria queries
• HQL queries if subselect fetching is used

In the case of HQL queries you have to use left join fetch :

em.createQuery("select f from Foo f left join fetch f.bar where f.id = :id")
    .setParameter("id", id)
    .getSingleResult();