如何在 SQLAlchemy 中为关系设置默认值？

Question

我的 Flask-SQLAlchemy 项目的用户模型中有以下关系字段，我希望能够设置默认值，以便用户自动关注自己。有没有办法在 SQLAlchemy 中的关系中设置默认值？那会是什么样子？

followed = db.relationship('User', secondary=followers, primaryjoin=(followers.c.follower_id == id),
                   secondaryjoin=(followers.c.followed_id == id),
                   backref=db.backref('followers', lazy='dynamic'),
                   lazy='dynamic')

下面的函数是这样的：

    def follow(self, user):
        # returns an object if it succeeds, None if it fails
        if not self.is_following(user):
            self.followed.append(user)
            return self

我一直在使用 Miguel Grinberg 的教程作为参考，但我的项目设置为我无法像他那样在 after_login 中执行 db.session.add(user.follow(user)) 。我之前在 before_first_request 中做过，但是单元测试有问题，因为用户没有登录，因此是匿名的。让用户在初始化时默认遵循自己的行为可以解决这个问题。感谢您的帮助！

Answer 1

您的用户模型添加新方法。

@staticmethod
def follow():
  if not user.is_following(user):
        user.follow(user)
        db.session.add(user)
        db.session.commit()    

Answer 2

我也有类似的问题：

class User(Base):
__tablename__ = "users"

id: Mapped[int] = mapped_column(primary_key=True)
email: Mapped[str] = mapped_column(String(30), nullable=False)
full_name: Mapped[str] = mapped_column(String, nullable=False)
is_online: Mapped[bool] = mapped_column(Boolean, default=True)

followings: Mapped["list[User]"] = relationship( # !!!problem is here!!!!
    "User",
    secondary="follower_associations",
    primaryjoin="User.id == FollowerAssociation.follower_id",
    secondaryjoin="User.id == FollowerAssociation.following_id",
    uselist=True
)


class FollowerAssociation(Base):
__tablename__ = "follower_associations"

id: Mapped[int] = mapped_column(primary_key=True)

follower_id: Mapped[int] = mapped_column(ForeignKey(
    User.id, 
    name="fk_follower_id", 
    ondelete="CASCADE"
))

following_id: Mapped[int] = mapped_column(ForeignKey(
    User.id,
    name="fk_following_id",
    ondelete="CASCADE"
))

follower: Mapped[User] = relationship(User, foreign_keys=[follower_id])
following: Mapped[User] = relationship(User, foreign_keys=[follower_id])

更改后问题解决了：

followings: Mapped["list[User]"] = relationship( 

到

followings: Mapped[list["User"]] = relationship(