SQLAlchemy 不理解在过滤器中使用关系的情况。在你的例子order.events.corporate
中。
我在尝试这样做时遇到以下异常:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object associated with Order.events has an attribute 'corporate'
我建议考虑使用SQL Alchemy 关系文档页面中描述的AssociationObject模式。
所以查询将是:
session.query(Order).filter(and_(EventsAssoc.type=="corporate",Event.name=="Big Corporation"))
查看完整示例如何定义模式和创建对象。
from sqlalchemy import *
from sqlalchemy import create_engine, orm
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
metadata = MetaData()
Base = declarative_base()
Base.metadata = metadata
class Event(Base):
__tablename__ = 'event'
id = Column(Integer, Sequence("event_seq"), primary_key=True)
name = Column(String(32))
def __repr__(self):
return "%s(name=\"%s\",id=\"%s\")" % (self.__class__.__name__,self.name,self.id)
class EventsAssoc(Base):
__tablename__ = 'events'
id = Column(Integer, Sequence("events_seq"), primary_key=True)
left_id = Column(Integer, ForeignKey('order.id'))
right_id = Column(Integer, ForeignKey('event.id'))
# order_id = Column(Integer, ForeignKey('order.id'), primary_key=True)
# event_id = Column(Integer, ForeignKey('event.id'), primary_key=True)
type = Column(Enum('corporate', 'personal', name='enum_ev_type'))
event = relationship(Event, backref="order_assocs")
def __repr__(self):
return "%s(events=%r,id=\"%s\")" % (self.__class__.__name__,self.event,self.id)
class Order(Base):
__tablename__ = 'order'
id = Column(Integer, Sequence("order_seq"), primary_key=True)
name = Column(String(127))
events = relationship(EventsAssoc)
def __repr__(self):
return "%s(name=\"%s\",id=\"%s\")" % (self.__class__.__name__,self.name,self.id)
db = create_engine('sqlite:////temp/test_assoc.db',echo=True)
#making sure we are working with a fresh database
metadata.drop_all(db)
metadata.create_all(db)
sm = orm.sessionmaker(bind=db, autoflush=True, autocommit=True, expire_on_commit=True)
session = orm.scoped_session(sm)
o = Order(name="order1")
ea_corp = EventsAssoc(type="corporate")
ea_corp.event = Event(name="Big Corporation")
ea_pers = EventsAssoc(type="personal")
ea_pers.event = Event(name="Person")
o.events.append(ea_corp)
o.events.append(ea_pers)
session.add(o)
session.flush()
query = session.query(Order).filter(and_(EventsAssoc.type=="corporate",Event.name=="Big Corporation"))
for order in query.all():
print order
print order.events
这是 sqlalchemy 生成的查询:
SELECT "order".id AS order_id, "order".name AS order_name
FROM "order", events, event
WHERE events.type = ? AND event.name = ?
('corporate', 'Big Corporation')
PS 为了增强关联对象模式,以便直接访问 EventsAssoc 对象是可选的,SQLAlchemy 提供了关联代理扩展