Question

下面是一个假的多对多表结构，比如客户订购事件。理想情况下，我希望能够实现的是使用不同的关系名称进行隐式查询和设置。

例如（假设 init 代码创建关联对象）

order=order()
order.events.corporate.name = "Big Corp"

这会将event.type（enum）设置为“corporate”，将event.name设置为“Big Corp”。类似地。

print session.query(Order).filter(order.events.corporate.name == "Big Corp")

这只会找到具有关联event.type =“corporate”的事件记录。（琐碎的例子，但没有必要，但你明白了）

同样使用order.events.personal.name将使用event.type =“personal”设置/查询相应的记录

非常感谢您帮助了解实现此功能的最佳方式。

Base = declarative_base()

class Order(Base):
    __tablename__ = 'order'
    id                  = Column(Integer, primary_key=True)
    event_id            = Column(Integer, ForeignKey('events.id'))

    events = relationship("Events")

class Events(Base):
    __tablename__ = 'events'
    order_id            = Column(Integer, ForeignKey('order.id'), primary_key=True)
    event_id            = Column(Integer, ForeignKey('event.id'), primary_key=True)

    corporate = relationship("Event")
    personal  = relationship("Event")
    event     = relationship("Event")

class Event(Base):
    __tablename__ = 'event'
    id                  = Column(Integer, primary_key=True)
    type                = Column(Enum('corporate', 'personal', name='enum_ev_type'))
    name                = Column(String(32))

Answer 1

SQLAlchemy不了解在过滤器中使用关系时的情况。在您的示例中order.events.corporate。

我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'

我建议您考虑使用AssociationObject中描述的SQL Alchemy Relationships documentation page模式。

所以查询将是：

session.query(Order).filter(and_(EventsAssoc.type=="corporate",Event.name=="Big Corporation"))

请参阅完整示例，了解如何定义架构和创建对象。

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要增强关联对象模式，以便可以直接访问EventsAssoc对象，SQLAlchemy提供Association Proxy extension

SQLAlchemy - 使用Relationships按类行类型进行筛选

1 个答案: