Flask-SQLAlchemy - 模型没有属性“foreign_keys”

我用 Flask-SQLalchemy 创建了 3 个模型：User、Role、UserRole

role.py:

class Role( ActiveRecord, db.Model ):

    __tablename__ = "roles"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    name = db.Column( db.String( 24 ), unique = True )
    description = db.Column( db.String( 90 ) )

    users = db.relationship( "User", secondary = "UserRole", \
        backref = db.backref( "roles" ) )

user.py:

class User( db.Model, ActiveRecord ):

    __tablename__ = "users"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    email = db.Column( db.String( 90 ), unique = True )
    password = db.Column( db.String( 64 ) )

    #   Relations
    roles = db.relationship( "Role", secondary = "UserRole", \
        backref = db.backref( "users" ) )

用户角色.py：

class UserRole( ActiveRecord, db.Model ):

    __tablename__ = "user_roles"

    #   Schema
    user_id = db.Column( db.Integer, db.ForeignKey( 'users.id' ), primary_key = True )
    role_id = db.Column( db.Integer, db.ForeignKey( 'roles.id' ), primary_key = True )

如果我尝试（在控制台中）通过以下方式获取所有用户User.query.all() I get AttributeError: 'NoneType' object has no attribute 'all'如果我再试一次，我会收到另一个错误：

sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers.  Original exception was: type object 'UserRole' has no attribute 'foreign_keys'

任何人都可以阐明我到底做错了什么吗？我认为几个月前这段代码运行正常，但我最近更新了 SQLAlchemy、Flask 和 Flask-SQLAlchemy，它就停止了。这只是一个副业项目。

这里有点困难，因为您正在使用一些未知的基类，例如“ActiveRecord”等。然而，看起来“次要”论点是错误的：

class User( db.Model, ActiveRecord ):

    __tablename__ = "users"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    email = db.Column( db.String( 90 ), unique = True )
    password = db.Column( db.String( 64 ) )

    #   Relations
    roles = db.relationship( "Role", secondary = "UserRole", \
        backref = db.backref( "users" ) )

secondary需要参考一个Table对象，而不是映射的类，如果通过字符串名称那么它将是"user_roles":

    roles = db.relationship( "Role", secondary = "user_roles", \
        backref = db.backref( "users" ) )