gistfile1.py

class Shop(Base):
    __tablename__ = 'shop_config'

    id = Column('site_id', Integer, primary_key=True)


class Order(Base):
    __tablename__ = 'shop_order'

    id = Column(Integer, primary_key=True)
    site_id = Column(Integer)


class AbstractStatus(object):
    id = Column(Integer, primary_key=True)
    time_stamp = Column(DateTime(timezone=True))
    status = Column(String)
    notes = Column(Unicode(100))

    @declared_attr
    def order_id(cls):
        return Column(Integer, ForeignKey(Order.id))


class Status(AbstractStatus, Base):
    __tablename__ = 'shop_orderstatus'

    order = relationship(Order, backref=backref(
        'statuses', lazy=True,
        order_by=AbstractStatus.time_stamp.desc()
    ))


class CurrentStatus(AbstractStatus, Base):
    """
    This is a mapped view which holds the last status for each order.
    """
    __tablename__ = 'shop_orderstatus_current'

    order = relationship(Order, backref=backref(
        'current_status', lazy=False, uselist=False
    ))


Shop.orders = relationship(
    Order, viewonly=True, lazy='dynamic',
    primaryjoin=((Shop.id == foreign(Order.site_id)) & (Order.status != '')),
    order_by=lambda: Order.current_status.timestamp,  # <-- What can I put here to order by the current timestamp?
)