Hi,
I ended up in a weird case in which, if I call "find()" on an entity manager for a given id of an entity, I get a different results than using a Query object. By looking at the generated SQL, those are different: one is a single query using left outer joins, whereas the other is a sequence of selects.
Consider this example: class A has a eager list of B, which in turn has a eager list of C:
Code:
private long initData(){
A a = new A();
B b0 = new B();
B b1 = new B();
a.getListB().add(b0);
a.getListB().add(b1);
C c0 = new C();
C c1 = new C();
C c2 = new C();
C c3 = new C();
b0.getListC().add(c0);
b1.getListC().add(c1);
b1.getListC().add(c2);
b1.getListC().add(c3);
assertTrue(persistInATransaction(a, b0, b1, c0, c1, c2, c3));
return a.getId();
}
here, an A has 2 Bs. First B has 1 C, whereas the second B has 3 Cs.
The following test show the difference in behavior:
Code:
@Test
public void test(){
long id = initData();
EntityManager em = factory.createEntityManager();
Query query = em.createQuery("select a from A a where a.id="+id);
System.out.println("\n* Going to execute JPQL query");
A a = (A) query.getSingleResult();
/*
Hibernate: select a0_.id as id1_0_ from A a0_ where a0_.id=1
Hibernate: select listb0_.A_id as A_id1_1_0_, listb0_.listB_id as listB_id2_1_0_, b1_.id as id1_2_1_ from A_B listb0_ inner join B b1_ on listb0_.listB_id=b1_.id where listb0_.A_id=?
Hibernate: select listc0_.B_id as B_id1_3_0_, listc0_.listC_id as listC_id2_3_0_, c1_.id as id1_4_1_ from B_C listc0_ inner join C c1_ on listc0_.listC_id=c1_.id where listc0_.B_id=?
Hibernate: select listc0_.B_id as B_id1_3_0_, listc0_.listC_id as listC_id2_3_0_, c1_.id as id1_4_1_ from B_C listc0_ inner join C c1_ on listc0_.listC_id=c1_.id where listc0_.B_id=?
*/
assertEquals(2, a.getListB().size());
em.clear();
System.out.println("\n* Going to execute 'em.find'");
A aFromFind = em.find(A.class, id);
//Hibernate: select a0_.id as id1_0_0_, listb1_.A_id as A_id1_1_1_, b2_.id as listB_id2_1_1_, b2_.id as id1_2_2_, listc3_.B_id as B_id1_3_3_, c4_.id as listC_id2_3_3_, c4_.id as id1_4_4_ from A a0_ left outer join A_B listb1_ on a0_.id=listb1_.A_id left outer join B b2_ on listb1_.listB_id=b2_.id left outer join B_C listc3_ on b2_.id=listc3_.B_id left outer join C c4_ on listc3_.listC_id=c4_.id where a0_.id=?
assertEquals(4, aFromFind.getListB().size());
em.close();
}
When I use Query to find A, it correctly gets 2 Bs. However, when I use "find", I get 4. I do understand this is an expected behavior when outer joins are involved (
https://developer.jboss.org/wiki/HibernateFAQ-AdvancedProblems#jive_content_id_Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword), but still for me it is very surprising that Query and "find" behaves completely differently. Regardless of what should be the expected results (2 or 4 Bs), why do they behave differently? Can the fact that they are different be considered a bug? Or rather an expected behavior?
thanks
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