Flask-SQLAlchemy - 模型没有属性'foreign_keys'

Question

我用 Flask-SQLalchemy 创建了 3 个模型：用户、角色、用户角色

角色.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" ) )

user_role.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User.query.all() 获取所有用户，我会得到AttributeError: 'NoneType' object has no attribute 'all'，如果我再试一次，我会收到另一个错误消息：

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'

谁能阐明我到底做错了什么？我想几个月前我的这段代码运行良好，但我最近更新了 SQLAlchemy、Flask 和 Flask-SQLAlchemy，但它停止了。这只是一个附带项目。

Answer 1

这里有点困难，因为您使用了一些未知的基类，例如“ActiveRecord”等。但是，看起来“次要”参数是错误的：

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 需要引用 Table 对象，而不是映射类，如果按字符串名称，那么它将是 "user_roles"：

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