My question is more of a best practices question on how to implement unowned relationships with Google App Engine. I am using JDO to do my persistence and like recommended in the google docs I'm persisting my list of unowned relationships like so:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class User implements Serializable, UserDetails {
...

    @Persistent
    private List<Key> groups;
...
}

Now I came across my predicament when I went to query that list of objects using they Key object. So when I get my list of group keys in order to actually return a list of Group objects I have to do a look up on that key to get the object. My question is what is the recommended way of doing a unowned look up on a model object?

Should I have an instance of the PersistanceManagerFactory on my Model object so I can do a lookup?

Should I have an instance of my GroupDAO object on my Model object so I can do a look up?

Should I have a Utility to do this type of lookup?

I'm new to this so I just want to know which is the best way to do this. Thanks.