Hi,

I'm trying to build a query using the Criteria API that can filter results on a joined sub-class.

To illustrate the problem let's say I've got a class "Group" with a unidirectional one-to-many relationship to a class "User", this class having a subclass "ForeignUser" containing a field "country".

Using this schema, I want to retrieve all the external users - from a given group - that match a given country.

My first shot at that was :

...tx stuff...
Criteria groupFilter = session.createCriteria(Group.class);
groupFilter.add( Expression.eq("id", 1 ));
Criteria foreignUserFilter = groupFilter.createCriteria("users");
foreignUserFilter.add( Expression.eq("country","Belgium"));
List results = groupFilter.list();

In result Hibernate throws an exception saying that the class "User" has no field named "country" (...and it doesn't indeed). The problem here is that I don't see how to tell Hibernate to search for users of type ForeignUser only.

How could I achieve that, bearing in mind that :
- The (unalterable) unidirectional nature of the relationship between Group and User prevents me from starting my query with a Criteria set on class ForeignUser (because I won't be able to join to "Group" and filter on group id from there)
- I know it can be done in HQL, but I'd rather get it done with the Criteria API
- That schema is using the "table per class" hierarchy

Thanks,
Cédric

This is a common question in this forum.

To access fields from an internal class you must enter the full name of
the property. In your case if ForeignUser is named fUser in your hibernate
mapping file, to access it's country property you must use :

fUser.country

Hi dpmihai,

Thanks for your quick reply. In my schema "ForeignUser" is not an inner class of "User", but a sub-class.

The class inheritance has been defined in the HBM as follow :



which is quite different from an internal class.

Regards,
Cédric

In this case you cannot. If you want to look for ForeignUsers use a criteria
with this class. There is no way to acces country property from User.

For the record, I managed to do this in HQL by filtering on the subclass first ("ForeignUser") and then joining back to the "Group" class using an outer-join (aka "theta-style join" or "cartesian product").

Less effective since it requires 3 tables to do the join (where only 2 should be needed).

The HQL that returns the wanted results looks like :



As of now, the Criteria API doesn't support outer joins.

Cédric