The <any> tag (Hibernate Core) seems to be a way how to implement polymorphic relations with the table-per-contrete-class strategy and a discriminator.

However, JPA/EJB 3.0 or some Hibernate Annotations specific extensions would be the prefered technology. So, the general question is if there is a way to use the <any> principle with JPA?

Some thoughts on this:

I know you could mix hbm.xml files with JPA Annotations, but there are some concerns using a mixture of "two" technologies in the project team.

Another alternative I would see is extending Hibernate Annotations ourselves - any ideas, comments or experiences on this approach?

With plain JPA, hmm ... as you are aware, you can use it with H3 - which is JBoss JPA implementation ;-).


We use it - we have a lot of 'legacy' entities - which we don't feel like annotating - just extra work for entities that we use all the time - User, Address, Company, ...


You can always submit a patch of additional Hibernate Annotations. :-)

Rgds, Ales

Thank you Ales for sharing your opinions. You said your experience with mixing JPA and Hibernate Core mechanisms was positive. Could you describe your solution a little more in detail (for which part are you using JPA?)

Also, I see some limitations of the <any> solution. OK, it does not fit in the EJB 3.0 forum, but since we started already...

First, I did not figure out yet how to use any with a join over multiple columns. The PK referenced by <any> is a composite-id:
<composite-id name="oid" class="SomeOid">
<key-property name="idH" column="H"/>
<key-property name="idM" column="M"/>
<key-property name="idL" column="L"/>
</composite-id>

The <any> mapping:
<any name="anyRel" id-type="SomeOid" meta-type="integer">
<meta-value value="1" class="Test1"/>
<meta-value value="2" class="Test2"/>
<meta-value value="3" class="Test3"/>
<column name="XyzC"/>
<column name="XyzH"/>
<column name="XyzM"/>
<column name="XyzL"/>
</any>
Like this, Hibernate has problem with the type:
org.hibernate.MappingException: property mapping has wrong number of columns: HasAny.anyRel type: object

I would have a CompositeUserType for the SomeOid class, but I could not find a syntax how to tell it Hibernate to use it for the <any> mapping.

Second, am I right that there is no way to define bidirectional association with <any> on one side?

We are mostly using Hibernate - with Session, SessionFactory, ... in enterprise beans with @PersistenceContext, @PersistenceUnit - as JPA is a subset of H3.
But we have a generic Session bean that uses EntityManager - which uses Java5 generics,when Session is not.


Uf, never used <any>.