flask web第九章self.role.permissions & permissions 报错

Question

class Role(db.Model):
    __tablename__ = 'roles'
    users = db.relationship('User', backref='role', lazy='dynamic')
    permissions = db.Column(db.Integer)
class User(db.Model, UserMixin):
    __tablename__ =  'users'
    #………………
    def can(self, permissions):
        return self.role is not None and\
                  (self.role.permissions & permissions) == permissions

错误：
Traceback (most recent call last):
File "/home/hemu/flaskoo/tests/test_user_model.py", line 27, in test_roles_and_permissions

self.assertTrue(u.can(Permission.WRITE_ARTICLES))

File "/home/hemu/flaskoo/app/models.py", line 119, in can

return self.role is not None and (self.role.permissions & permissions) == permissions

TypeError: unsupported operand type(s) for &: 'NoneType' and 'int'
不理解为什么报错？
我的理解是，self.role.permissions 引用到class Role 的 permissions属性，这个已经明确定义是Integer类型了，为什么还报错是NoneType呢
初学者，求大神指点

Answer 1

你没有在shell里先调用insert_role插入roles吧，permissions可能还没有赋值

Answer 2

看一下你的roles表中permissions字段有没有值