[b]Hibernate version: JBoss EJB-3RC8[/b]

I have a simple class hierarchy that uses joined inheritance:
[code]
@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class MaterialMaster {
private String externalId;
}

@Entity
@PrimaryKeyJoinColumn(name="ID")
public class SparePartMaster extends MaterialMaster {

}
[/code]

This hierarchy is referenced by another class:
[code]
@Entity
public class RecallOrderLine {
@ManyToOne(fetch=FetchType.LAZY, optional=false)
private RecallOrder recallOrder;

@OneToOne(fetch=FetchType.LAZY, optional=false)
private MaterialMaster material;
}
[/code]

When I query
[code]
SELECT r FROM RecallOrderLine r
WHERE r.recallOrder=:recallOrder
AND r.material =:material
[/code]
the returned RecallOrderLine has a SparePartMaster instance as expected.

Now when I query
[code]
SELECT r FROM RecallOrderLine r
WHERE r.recallOrder=:recallOrder
AND r.material.externalId =:matExtKey
[/code]
the returned RecallOrderLine has a MaterialMaster instance only!

My DB is correct. So it must be a bug in Hibernate.

It is just because of @OneToOne(fetch=FetchType.LAZY, optional=false).

When fetching an Entity in Lazy mode a proxy of the referenced entity is returned. So in your case a proxy for MaterialMaster will be created (which is a subclass of MaterialMaster). So that proxy could not be SparePartMaster.

I believe the best way to solve this problem is to set fetch=FetchType.EAGER.
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don't forget credits

Okay, thanks. I understand now, why it's doing that.

It's quite a stupid trap to fall in. When I decide to add a discriminator column to MaterialMaster to designate the type explicitely, then Hibernate definitely has the possibility to provide the correct subclass. Do you know if it does that?

This has nothing to do with the discriminator column and you get different results because in the second case you do not have the material instance in your persistence context. use @LazyToOne(NO_PROXY) and enhance your classes if you can't live wo using instanceof

Thanks emmanuel. Stupid question: how do I enable byte code enhancement for this class? The LazyToOne doesn't seem to work out of the box.

chek the hibernate reference documentation for buildtime enhancement, there is a descrimtion of the process