python - SQLAlchemy 多态关联

Question

我尝试通过 SQLAlchemy 库实现多态关联并使用示例:

discriminator_on_association .

但是有一处不符合我的情况。在示例中:创建地址对象，然后将它们添加到供应商或客户(因此地址表具有指向供应商和客户表的多态外键以及指向地址的供应商和客户对象反向引用)。当 Address 对象添加到这些表中时，SQLAlchemy 会自动解决如何在表上分配 Id。然后可以使用地址的“父”字段获取供应商或客户对象。

尽管在我的例子中，我需要首先创建地址对象，然后为地址父对象分配一个对象(例如，公司，在示例中是供应商和客户)。

在我的案例中使用多态关联的例子:

engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)

session = Session(engine)

address = Address(street='2569 west elm', city="Detroit", zip="56785")

cust = Customer(name="Tester")
supl = Supplier(company_name="Ace Hammers")

address.parent = supl

session.add_all([address])

session.commit()

但是如果我尝试将此模式应用于我的案例而不进行修改，我会收到下一条错误消息:

Traceback (most recent call last):  File "discriminator_on_related.py", line 131, in     address.parent = supl  File "C:\Python27\lib\site-packages\sqlalchemy-0.9.3-py2.7-win32.egg\sqlalchemy\ext\associationproxy.py", line 271, in __set__    setattr(obj, self.target_collection, creator(values))TypeError: __init__() takes exactly 1 argument (2 given)

我应该如何修改此模式以使其工作？

附言对不起，如果这是一个微不足道的问题(SQLAlchemy association_proxy 对我来说看起来像是某种魔法)。

Answer 1

对不起所有被这个问题打扰的人。可能答案对某人有用。答案实在是太简单了。我的主要错误是我使用了一个复杂的模式示例作为我的案例的基础。要解决此任务，只需将其拆分为子任务即可。因此，此任务包括连接表的多态继承(使用 SQLAlchemy 很容易实现)和在公共(public)(父)表上设置外键。这是显示下一个代码片段:

@as_declarative()
class Base(object):
    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()
    id = Column(Integer, primary_key=True)


class CompanyInterface(Base):
    discriminator = Column(String)

    __mapper_args__ = {"polymorphic_on": discriminator}


class Address(Base):
    street = Column(String)
    city = Column(String)
    zip = Column(String)
    company_id = Column(Integer, ForeignKey(CompanyInterface.id))
    company = relationship(CompanyInterface)

    def __repr__(self):
        return ("%s(street=%r, city=%r, zip=%r, company=%r)" %
                (self.__class__.__name__, self.street, self.city, self.zip, self.company))


class Customer(CompanyInterface):
    id = Column(Integer, ForeignKey(CompanyInterface.id), primary_key=True)
    name = Column(String)
    __mapper_args__ = {"polymorphic_identity": "Customer"}


class Supplier(CompanyInterface):
    id = Column(Integer, ForeignKey(CompanyInterface.id), primary_key=True)
    company_name = Column(String)
    __mapper_args__ = {"polymorphic_identity": "Supplier"}


engine = create_engine('sqlite:///test/test_me.db', echo=False)
Base.metadata.create_all(engine)

session = Session(engine)

address1 = Address(street='test-1', city="Detroit", zip="56785")
address2 = Address(street='test-2', city="Phoenix", zip="110322")
address3 = Address(street='test-3', city="Washington", zip="432414")

supl1 = Supplier(company_name="Supplier-1 TEST")
supl2 = Supplier(company_name="Supplier-2 TEST")
cust1 = Customer(name="Customer-1 TEST")
cust2 = Customer(name="Customer-2 TEST")

address1.company = supl1
address2.company = cust1
address3.company = cust1

session.add_all([address1, address2, address3])

session.commit()

address3.company = supl2

session.commit()

print "PRINTING, TOTAL = %s" % session.query(Address).count()
for address in session.query(Address):
    print "ADDRESS = %s" % address