created_by = Column("created_by", Integer(), ForeignKey('users.user_id'), nullable=True)

    created_on = Column('created_on', DateTime(timezone=False), nullable=False, default=datetime.datetime.now)

    type_ = Column('type', Unicode(256))

    created_by_user = relationship('User')

    notifications_to_users = relationship('UserNotification', lazy='joined',

                                          cascade="all, delete, delete-orphan")

    @property

    def recipients(self):

        return [x.user for x in UserNotification.query()\

                .filter(UserNotification.notification == self)\

    @classmethod

    def create(cls, created_by, subject, body, recipients, type_=None):

        if type_ is None:

            type_ = Notification.TYPE_MESSAGE

        notification = cls()

        notification.created_by_user = created_by

        notification.subject = subject

        notification.body = body

        notification.type_ = type_

        notification.created_on = datetime.datetime.now()