[hibernate-issues] [Hibernate-JIRA] Created: (HHH-5822) Entities can't also be MappedSuperclasses

[Laran Evans (JIRA)]

Entities can't also be MappedSuperclasses
-----------------------------------------

                 Key: HHH-5822
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5822
             Project: Hibernate Core
          Issue Type: Bug
          Components: core
    Affects Versions: 3.6.0.Beta1, 3.5.2
            Reporter: Laran Evans


I recently upgraded Hibernate and discovered trouble.

We've got a situation where we have two classes mapped to a single table.

@MappedSuperclass
@Entity
@Table(name="thing")
class ThingLite {
// ... basic, shared fields
}

@Entity
@Table(name="thing")
class Thing extends ThingLite {
// ... extra fields
}

Both classes do truly map to the same table. ThingLite just doesn't pull back all of the fields that Thing does. The table contains a blob column which we don't need most of the time.

In retrospect, we could have used a joined table strategy, separating the blob column and the fields specific to Thing into a separate table. But we didn't. And going back now to redesign the tables isn't an option.

HHH-5125 makes it no longer possible to have a superclass that is both an Entity and a MappedSuperclass, and I'm not convinced that it shouldn't be allowed.

Do you guys agree that it should be possible? I can't think of a specific reason that it shouldn't be.

An alternative approach that I thought of would be to use a joined inheritance approach, joining on the same table to get the additional fields for Thing. When I tried it however I got errors relating to circular references. I don't quite understand why this should be the case. Niether Thing nor ThingLite have references to one another other than the fact that Thing extends ThingLite.

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