如何从另一个模块添加到现有映射类的关系

Question

我有两个模块。第一个是：

# module_1.py
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column

class Base(DeclarativeBase):
    pass

class User(Base):
    id: Mapped[int] = mapped_column(primary_key=True)
    name: Mapped[str]

第二个是：

# module_2.py
from sqlalchemy.orm import Mapped, mapped_column

from .module_1 import Base, User

class Address(Base):
    id: Mapped[int] = mapped_column(primary_key=True)
    city: Mapped[str]
    user_id: Mapped[int] = mapped_column(
        ForeignKey('user.id'), nullable=False
    )

    user: Mapped['User'] = relationship(back_populates='addresses')

现在的问题是我不知道如何添加

addresses: Mapped[Set['Address']] = relationship(back_populates='user')

从

User

 内部

到

module_2.py

类，无需修改

module_1.py

文件。顺便说一句，我不想使用旧的

backref

关系参数。

Answer 1

您可以尝试在 User 类定义后添加

addresses

关系：

from sqlalchemy.orm import relationship
from sqlalchemy.orm.base import class_mapper
from sqlalchemy.orm.relationships import RelationshipProperty

from .module_1 import User

mapper = class_mapper(User)
mapper.add_property(
    'addresses',
    relationship(
        Address,
        back_populates='user',
        uselist=True
    )
)