python - 过滤 SQLAlchemy 关系

Question

我正在使用 Pyramid + SQLAlchemy 并进行以下设置

from sqlalchemy import orm
from __init__ import user_table  
from device import Device

class User(object):
  def __repr__(self):
    return 'User: ' + self.username

orm.mapper(User, user_table, properties={
  'devices': orm.relation(Device, backref='owner')
})

访问时如何添加过滤器 user.devices ?当我尝试时 user.devices.filter(Device.platform==1).all() ，我收到以下错误:

'InstrumentedList' object has no attribute 'filter'

Answer 1

您可以使用 Query-Enabled Property :

class User(object):
    def __repr__(self):
        return 'User: ' + self.username

    # property
    @property
    def devices_filtered(self):
        return object_session(self).query(Device).with_parent(self).filter(Device.platform==1).all()

    # or simply a method
    def devices_filtered(self, platform):
        return object_session(self).query(Device).with_parent(self).filter(Device.platform==platform).all()

或查看 Dynamic Relationship Loaders :

orm.mapper(User, user_table, properties={
  'devices': orm.relation(Device, backref='owner', lazy='dynamic')
})

# ...
user = session.query(User).get(_some_user_id)
devices = user.devices.filter(Device.platform==platform).all()

只需阅读引用文档即可获得有关这些主题的完整说明。