在SQLAlchemy基类中定义抽象方法

Question

从http://docs.sqlalchemy.org/en/improve_toc/orm/extensions/declarative/mixins.html#augmenting-the-base我看到你可以在基类中定义方法和属性.

我想确保所有子类都实现一个特定的方法.但是,在尝试定义这样的抽象方法时:

import abc
from sqlalchemy.ext.declarative import declarative_base

class Base(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def implement_me(self):
        pass

Base = declarative_base(cls=Base)

class Child(Base):
    __tablename__ = 'child'

我收到了错误 TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

我试图找到一些文档或示例来帮助我,但是很简单.

Answer 1

看起来你可以传递一个元类declarative_base.默认元类是DeclarativeMeta-所以,我认为关键是创建一个新的元类是的混入abc.ABCMeta和DeclarativeMeta:

import abc
from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta

class DeclarativeABCMeta(DeclarativeMeta, abc.ABCMeta):
    pass

class Base(declarative_base(metaclass=DeclarativeABCMeta)):
    __abstract__ = True
    @abc.abstractmethod
    def implement_me(self):
        """Canhaz override?"""

^{*未经测试}