Question

使用SQLAlchemy，我希望继承一个包含多个主键的模型，例如：

from sqlalchemy import (Column, Integer, create_engine, ForeignKey,
                        ForeignKeyConstraint, UniqueConstraint)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr


#engine = create_engine('sqlite:///memory')
engine = create_engine('postgres:///memory')
Base = declarative_base()


class Test(Base):
    __tablename__ = 'test'
    id = Column(Integer, primary_key=True)
    id2 = Column(Integer, primary_key=True)


class Test2(Test):
    __tablename__ = 'test2'
    id = Column(Integer, ForeignKey('test.id'), primary_key=True)
    id2 = Column(Integer, ForeignKey('test.id2'), primary_key=True)

    @declared_attr
    def __table_args__(cls):
        return (
            UniqueConstraint(cls.id, cls.id2),
            ForeignKeyConstraint([cls.id, cls.id2], 
                                 [Test.id, Test.id2]),
        )

    @declared_attr
    def __mapper_args__(cls):
        return {
            'inherit_condition': (cls.id == Test.id and cls.id2 == Test.id2),
        }


Base.metadata.create_all(engine)

继承仅使用一个主键列，这不是我的用例。我有两个String主键列，我使用SQLAlchemy的多态模式。我没有编写所有代码，无论是否有多态配置，问题都是一样的。

此代码适用于sqlite，但不适用于postgres，__table_args__在这里没用，我想念什么？

问候

Answer 1

我发现，必须删除column中的外键约束

from sqlalchemy import (Column, Integer, create_engine, 
                        ForeignKeyConstraint)
from sqlalchemy.ext.declarative import declarative_base


#engine = create_engine('sqlite:///memory')
engine = create_engine('postgres:///memory')
Base = declarative_base()


class Test(Base):
    __tablename__ = 'test'
    id = Column(Integer, primary_key=True)
    id2 = Column(Integer, primary_key=True)


class Test2(Test):
    __tablename__ = 'test2'
    # No foreign key here
    id = Column(Integer, primary_key=True)
    id2 = Column(Integer, primary_key=True)

    __table_args__ = (
        # this constraints must be the alone to Test model
        ForeignKeyConstraint([id, id2], [Test.id, Test.id2]),
    )


Base.metadata.create_all(engine)

SQLAlchemy，postgres继承具有多个主键列的模型

1 个答案: