SQLAlchemy多态关联

Question

我试图通过SQLAlchemy库实现多态关联，并将其用于示例：

discriminator_on_association。

但有一点与我的情况不符。在示例中：创建Address对象，然后将其添加到Supplier或Customer（因此Address表对Supplier和Customer表具有多态外键，而Supplier和Customer对象对Address具有backref）。当Address对象添加到这些表时，SQLAlchemy会自动解决如何在表上分配Id的问题。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Address对象，然后将一个对象分配给Address父对象（例如Company，例如它是Supplier和Customer）。

在我的案例中使用多态关联的示例：

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()

但如果我尝试将此模式应用于我的案例而不进行修改，则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)

我应该如何修改这个模式以使其工作？

很抱歉，如果这是一个很小的问题（SQLAlchemy association_proxy对我来说像是某种魔法）。

Answer 1

对不起，所有在这个问题上有麻烦的人。也许答案对某人有用。答案实在太简单了。我的主要错误是在我的案例基础上使用了一个复杂的模式示例。要解决此任务，只需要在子任务上拆分它。因此，这项任务包括具有联接表的多态继承（使用SQLAlchemy很容易实现）和在公共（父）表上设置外键。下面是下一段代码：

@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