Usually we would use `notification=notification`, instead of `x_id=x.id` -- this allows SQLAlchemy to handle the `flush` automatically (SQLAlchemy will detect dependencies, usually -- we only need to `flush` manually when dependency loops happen, like with `Context` in `ggrc_basic_permissions`.  This requires the `db.relationship` is configured correctly -- refer to the note about `backref` above in `models/notification.py`