The background here is integrating my JPA 2.1 work in with the Hibernate 5.0 metamodel branch. One of the things the EntityManagerFactory does when starting up is to build the JPA javax.persistence.metamodel.Metamodel. Today that process leverages the old Hibernate mapping code (org.hibernate.mapping). I will need to re-write this to leverage the new org.hibernate.metamodel code. I wanted to run the way I am thinking of attacking this past everyone to get feedback. Basically I want to have the *SessionFactory* take over responsibility for building it. 2 main reasons why: 1) First it would be more efficient. Today we loop over those mapping objects at least twice: once to create the persisters as part of SessionFactory building and then again later to build this JPA Metamodel as part of EntiytManagerFactory building. Once is better than twice when it comes to looping :) 2) I have this other idea where I'd really like to see JPA criterias useable in "native" Hibernate usage (Session/SessionFactory). Which would essentially require both javax.persistence.metamodel.Metamodel as well as javax.persistence.criteria.CriteriaBuilder to be available. Well technically any "criteria builder" that output the proper types could work; and I guess Metamodel is not strictly needed to build criterias aside from potentially populating the static generated metamodel classes. But it would be nice to have them. -- steve(a)hibernate.org http://hibernate.org