When I try to create new subnet and select some domain, it does not get saved and it unchecks the selected domain. It does not display any error message, but in logs (and through hammer) an error about invalid :subnet_domains relation can be found. It's caused by validations on relation entity which does not have foreign id, since we are about to save the new record. IMHO validations on relation entity should be removed, we never use the class directly and rely on active record to create it.