hql and polymorphism

[flopsi]

hi everybody,

i defined a hibernate entity with a polymorphic object property so the property's type is a base class and various object types can be assigned.
Everything worked out fine since now, but now i want to perform an hql query with a join like:

select objA from classA objA inner join fetch objA.prop objB ...

now in the result objA.prop is always an object of the base class (of course you might say), but i needed it to be the right subclass to be able to fetch all properties. casting to the subclass results in a ClassCastException.

is it possible to rewrite the query or do some other tricks so i retrieve an object of the right sublass here? of course i want to avoid executing an extra query for every result record...
by the way, i use table-per-class (joined) mapping strategy.

thanks a lot for opening my eyes,
best regards,
flo

[flopsi]

okay, declaring the base class abstract seems to force hibernate to look for subclasses. unfortunately this has some impact on the rest of my application, so the question remains:
is ther another way to force hibernate to do so?

thx + regards
flo

[rogermorituesta.rogermori.yahoo.com]

...but i needed it to be the right subclass to be able to fetch all properties. casting to the subclass results in a ClassCastException.

A polymorfic hql result set already contains runtime instances of the subclasses. So no casting is required.

If you want to query upon a specific subclass add a where clause to your hql.

Roger.

[flopsi]

hi roger,
maybe i miss something. I tried using the 'class' attribute like

select objA from classA objA inner join fetch objA.prop objB where objB.class=:classId

with binding the simple class name to the :classId parameter, but an exception was thrown:
java.lang.String cannot be cast to java.lang.Integer

the generated sql looks like:
...
        and case
            when objB_1_.id is not null then 1
            when objB_2_.id is not null then 2
            when objB_.id is not null then 0
        end=?

where objB_1_ and objB_2_ reference the subclass tables as i can see in the select. so maybe binding 0, 1 or 2 to the :classId param would help.
but how do i find out the correct number? is the hibernate generated statement fix so i can rely on the numbers shown here? or is it possible on the next execution the numbers have changed?

is there maybe another way to specify the concrete class?

thanks a lot
best regards
flo

[rogermorituesta.rogermori.yahoo.com]

Hi Florian:

Dealing with addresses (Geographic, email, web, phone, etc), I have a similar case with inheritance type JOINED. Yet, I have added a string column and a pre persist method to the base class in order to store the class name via entity listener (@PrePersist):

@PrePersist
public void prePersist(Object entity) {
    if (entity instanceof Address) {
     Address address = (Address)entity;
     String type = address.getClass().getSimpleName();
     address.setType(type);
         }
  }

Also this hql will work as well:

select objA 
from classA objA , subclassB objB
where objA.xxx = objB.yyy 

Regards.

Roger.