Hi!
I'm implementing a generic DAO object to execute CRUD operations on objects whose classes have been mapped on Hibernate. I'm using JPA annotations for the class mapping.

In order to construct some filter expressions used internally, this DAO object needs to obtain the name of the attribute that has been mapped as the object's id for a given persistent object. So for example, I give an persistent instance (returned by a criteria query) to the DAO object and need to retrieve the name of its id attribute:



...which in most cases will simply be "id", but might be something else.

Is this possible? I only have access to the entity manager originally used to retrieve the object. I don't have metamodel classes being generated.

Please let me know if you have any clues on how to obtain this information.

Thanks!
Eduardo Born

Use run-time annotations?

Yeah that could be but I didn't want to introduce one more piece in the puzzle. Hibernate already detects this property on all mapped entities, so I was looking for a way to use Hibernate to obtain that information without having to write my own annotations.

Regarding scanning for Hibernate annotations, that's not too good because I'd have to look for Hibernate annotations and JPA too, and that wouldn't work for entities mapped with XML files.

I don't think JPA provides any mechanism to gather such meta information. However you could use Hibernate's ClassMetaData to fetch this information.

http://docs.jboss.org/hibernate/core/3. ... adata.html

But to get the class meta data you will need a handle to the session factory. Guess if you look in the org.hibernate.ejb package you might get some ideas on how to get that...

http://docs.jboss.org/hibernate/core/3. ... -tree.html

That's exactly what I was looking for!!

Thank you!!!!
Eduardo

Actually, I was wrong on this one. JPA *does* provide this information using the Metamodel API (probably using the IdentifiableType interface).

http://download.oracle.com/javaee/6/api ... mmary.html