def ensureFriendNotExist(cls, **args): return ViewManager.ensureObjectNotExist(Friend, ErrorType.AlreadyAFriend, **args)
def ensureParticipationNotExist(cls, uid, pid): return ViewManager.ensureObjectNotExist(Participation, ErrorType.HaveParticipated, user_id=uid, project_id=pid)
def ensureUserNotExist(cls, **args): return ViewManager.ensureObjectNotExist(User, ErrorType.UsernameNotExist, **args)