import java.lang.String; @Entity public class User { @Id @GeneratedValue Long id; @NaturalId String system; @NaturalId String userName; ... } // use getReference() to create associations... Resource aResource = (Resource) session.byId( Resource.class ).getReference( 123 ); User aUser = (User) session.byNaturalId( User.class ) .using( "system", "prod" ) .using( "userName", "steve" ) .getReference(); aResource.assignTo( user ); // use load() to pull initialzed data return session.byNaturalId( User.class ) .using( "system", "prod" ) .using( "userName", "steve" ) .load();