I have a question regarding how the new TREAT downcasting is handled.

Currently we have the following models using JOINED inheritance.

AbstractBase { String value0; }
Child0 extends AbstractBase { String value1; }
Child1 extends AbstractBase { String value2; }

Now using the Criteria API (cb.treat(Root<X>, Class<T>)) we generate the following HQL:

select generatedAlias0.id, generatedAlias0.value0, treat(generatedAlias0 as Child0).value1
from AbstractBase as generatedAlias0

Now this gets translated to SQL as follows:

select abstractba0_.id as col_0_0_, abstractba0_.VALUE_0 as col_3_0_, abstractba0_1_.VALUE_1 as col_4_0_
from PCY_T_ABSTRACT_BASE abstractba0_
inner join PCY_T_CHILD_0 abstractba0_1_ on abstractba0_.id=abstractba0_1_.id
left outer join PCY_T_CHILD_1 abstractba0_2_ on abstractba0_.id=abstractba0_2_.id

For a JOINED-Inheritance setup it would seem that a LEFT JOIN is more appropriate here instead of the INNER JOIN used to pull in the CHILD_0 table.

Now my question is, is there anyway to force the joining of CHILD_0 to use a LEFT OUTER JOIN? From the JPA 2.1 API there appears to be no possibility of passing in a JoinedType value, but perhaps, there is a Hibernate-specific method which could be used instead?

Thanks,
Tito

Anybody has a solution for this? I noticed that Hibernate normally fetches polymorphic queries using a left outer join, but the moment you use "treat" it switches to an inner join. It seems to me that with this behavior Hibernate's "treat" implementation is useless for tables with joined inheritance.

In my case, I'm stuck with the Criteria API, which has even fewer options for working around the problem. At least with JPQL under JPA 2.1 you can join with arbitrary tables, so in theory you could left join the base class table with the table(s) representing the subclasses. Not so with the Criteria API.