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 Post subject: Duplicate joins when using fetch join
PostPosted: Wed Nov 30, 2016 1:03 pm 
Beginner
Beginner

Joined: Wed Sep 03, 2003 9:31 am
Posts: 26
I'm using Hibernate 5.2.5 and migrating my criteria queries to JPA criteria queries as suggested in the documentation.

Everything is working fine until now but I noticed something.

I have a CriteriaQuery like this:
Code:

CriteriaQuery<Entity1> query = builder.createQuery(Entity1.class);
Root<Entity1> fromEntity1 = query.from(Entity1.class);
Join<Entity1, Entity2> fromEntity2 = fromEntity1.join("entity2");
Join<Entity2, Entity3> fromEntity3 = fromEntity2.join("entity3");

fromEntity1.fetch("entity2").fetch("entity3"); // I assume I have to do that to fetch the entire objects, right?

List<Entity1> entities = hs.createQuery(query
      .select(fromEntity1)
      .where(builder.and(
            builder.equal(fromEntity1.get("idStatus"), 1),
            builder.like(fromEntity3.get("name"), "a%"))))
   .getResultList();


It works fine, but the in the generated SQL I have the same joins twice.

Code:
select
   entity1_.codcoligada as codcolig1_94_0_,
   entity2_.codcoligada as codcolig1_48_1_,
   entity3_.codigo as codigo1_47_2_,
from table1 entity1_
   inner join table2 aluno1_ on entity1_.codcoligada=aluno1_.codcoligada and entity1_.ra=aluno1_.ra
      inner join table3 pessoa2_ on aluno1_.codpessoa=pessoa2_.codigo
   inner join entity2 table2_ on entity1_.codcoligada=entity2_.codcoligada and entity1_.ra=entity2_.ra
      inner join table3 entity3_ on entity2_.codpessoa=entity3_.codigo
where entity1_.codstatus=1
   and (entity3_.nome like ?)


As you can see the generated sql has the entity2' and entity3' joins made twice. Is this correct or am I doing something wrong?


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 Post subject: Re: Duplicate joins when using fetch join
PostPosted: Wed Nov 30, 2016 3:17 pm 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1630
Location: Romania
Remove these lines:

Code:
Join<Entity1, Entity2> fromEntity2 = fromEntity1.join("entity2");
Join<Entity2, Entity3> fromEntity3 = fromEntity2.join("entity3");


and replace these lines:

Code:
Join<Entity1, Entity2> fromEntity2 = (Join<Entity1, Entity2>) fromEntity1.fetch("entity2");
Join<Entity2, Entity3> fromEntity3 = (Join<Entity2, Entity3>) fromEntity2.fetch("entity3");


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 Post subject: Re: Duplicate joins when using fetch join
PostPosted: Tue Dec 06, 2016 9:43 am 
Beginner
Beginner

Joined: Wed Sep 03, 2003 9:31 am
Posts: 26
Thanks for the tip.

I did it and got this compilation error:
Code:
Cannot cast from Fetch<Object,Object> to Join<Entity1,Entity2>


However when I did like this:
Code:
Join<Entity1, Entity2> fromEntity2 = (Join)fromEntity1.fetch("entity2");
Join<Entity2, Entity3> fromEntity3 = (Join)fromEntity2.fetch("entity3");


it worked, but I got a type safety compilation warning.

Anyway, the "double joins" are gone.


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