python - SQLAlchemy 多对多关系参数

Question

我正在使用 SQLAlchemy ORM 获取属于某个用户的角色，但出现以下错误

Could not determine join condition between parent/child tables on relationship AppRole.users - there are multiple foreign key paths linking the tables via secondary table 'app_user_role'. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference from the secondary table to each of the parent and child tables.

表格定义为:

class AppUserRole(Base_Write):
    __tablename__ = 'app_user_role'
    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime, server_default=text('NOW()'), nullable=False)
    created_by = Column(Integer, ForeignKey('app_user.id'), nullable=False)
    is_deleted = Column(Boolean, server_default='0', nullable=False)
    date_deleted = Column(DateTime)
    deleted_by = Column(Integer, ForeignKey('app_user.id'))
    user_id = Column(Integer, ForeignKey('app_user.id'), nullable=False)
    role_id = Column(Integer, ForeignKey('app_role.id'), nullable=False)
    date_assigned = Column(DateTime, nullable=False)


class AppRole(Base_Write):
    __tablename__ = 'app_role'
    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime, server_default=text('NOW()'), nullable=False)
    created_by = Column(Integer)
    is_deleted = Column(Boolean, server_default='0', nullable=False)
    date_deleted = Column(DateTime)
    deleted_by = Column(Integer, ForeignKey('app_user.id'))
    role_classification_id = Column(Integer, ForeignKey('app_role_classification.id'), nullable=False)
    role_code = Column(String(10), nullable=False, unique=True)
    role_name = Column(String(30), nullable=False)

    users = relationship("AppUser", secondary="app_user_role", back_populates="app_role")


class AppUser(Base_Write):
    __tablename__ = 'app_user'
    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime, server_default=text('NOW()'), nullable=False)
    created_by = Column(Integer, ForeignKey('app_user.id'), nullable=False)
    is_deleted = Column(Boolean, server_default='0', nullable=False)
    date_deleted = Column(DateTime)
    deleted_by = Column(Integer, ForeignKey('app_user.id'))
    username = Column(String(50), nullable=False, unique=True)

    roles = relationship("AppRole", secondary="app_user_role", back_populates="app_user")

正在运行的查询是:

for app_user in session.query(AppUser).\
filter(AppUser.is_deleted == False).filter(AppUser.id == user_id):
    #print the names of the roles assigned
    print(app_user.roles.role_name)

问题是，我还有其他表，我在其中定义了其他多对多关系参数，并且一切正常。在这里，尽管我不断收到该错误。 SO 上还有其他类似的问题，但尝试了不同的建议但没有运气。我尝试按照建议的错误进行操作，并使用了我之前的一个问题 here on SO但即使放置 foreign_keys 选项似乎也不起作用，尽管我必须承认我真的在猜测放置它的位置。

SQLAlchemy 版本 ==1.0.12，Postgresql 9.5

Answer 1

如错误消息所述，您有多个外键将 AppRole 链接到 AppUser，即 AppUserRole.user_id、AppUserRole .deleted_by，和AppUserRole.created_by，所以你需要指定foreign_keys参数:

class AppRole(Base):
    ...
    users = relationship("AppUser", secondary="app_user_role", 
                         foreign_keys=[AppUserRole.user_id, AppUserRole.role_id],
                         back_populates="roles")


class AppUser(Base):
    ...
    roles = relationship("AppRole", secondary="app_user_role",
                         foreign_keys=[AppUserRole.user_id, AppUserRole.role_id],
                         back_populates="users")