UniqueConstraint('user_id', 'notification_id'),

        {'extend_existing': True, 'mysql_engine': 'InnoDB',

         'mysql_charset': 'utf8'}

    )

    user_id = Column('user_id', Integer(), ForeignKey('users.user_id'), primary_key=True)

    notification_id = Column("notification_id", Integer(), ForeignKey('notifications.notification_id'), primary_key=True)

    read = Column('read', Boolean, default=False)

    sent_on = Column('sent_on', DateTime(timezone=False), nullable=True, unique=None)

    user = relationship('User', lazy="joined")

    notification = relationship('Notification', lazy="joined",

                                order_by=lambda: Notification.created_on.desc(),)

    def mark_as_read(self):

        self.read = True

        Session().add(self)

class Gist(Base, BaseModel):

    __tablename__ = 'gists'

    __table_args__ = (

        Index('g_gist_access_id_idx', 'gist_access_id'),

        Index('g_created_on_idx', 'created_on'),

        {'extend_existing': True, 'mysql_engine': 'InnoDB',

    )

    GIST_PUBLIC = u'public'

    GIST_PRIVATE = u'private'

    gist_id = Column('gist_id', Integer(), primary_key=True)

    gist_access_id = Column('gist_access_id', Unicode(250))

    gist_description = Column('gist_description', UnicodeText(1024))

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

    gist_expires = Column('gist_expires', Float(), nullable=False)

    gist_type = Column('gist_type', Unicode(128), nullable=False)

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

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

    owner = relationship('User')

    @classmethod

    def get_or_404(cls, id_):

        res = cls.query().filter(cls.gist_access_id == id_).scalar()

        if not res:

            raise HTTPNotFound

        return res

    @classmethod

    def get_by_access_id(cls, gist_access_id):