python - 修改 SqlAlchemy 模型时出现 Unhashable Type 错误

Question

我正在使用几乎从文档中复制的最基本的 Flask 应用程序，但收到一个非常烦人的错误。我已经能够追踪到它，但不知道如何解决它。我知道在实现 flask-security 时会出现问题，但错误来自 sqlalchemy 内部。有什么建议吗？

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
import logging
app = Flask(__name__)

app.config['DEBUG'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:' #

db = SQLAlchemy(app)

roles_users = db.Table('roles_users',
        db.Column('user_id', db.Integer(), db.ForeignKey('user.id')),
        db.Column('role_id', db.Integer(), db.ForeignKey('role.id')))

class Role(db.Model):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(80), unique=True)
    description = db.Column(db.String(255))

    def __init__(self, name, desc):
        self.name = name 
        self.description = desc

    def __repr__(self):
        return '<Role: {}>'.format(str(self.name))

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(255), unique=True)
    password = db.Column(db.String(255))
    roles = db.relationship('Role', secondary=roles_users,
                            backref=db.backref('users', lazy='dynamic'))

    def __init__(self, username, password):
        self.username = username
        self.password = password

    def __repr__(self):
        return '<User: {}>'.format(str(self.username))

def main():
    db.create_all()
    adminRole = Role('Admin', 'Unrestricted')
    adminUser = User('admin', 'adminpassword')
    adminUser.roles = [adminRole]
    db.session.add(adminUser)
    db.session.commit()
    app.run(debug=True)

if __name__ == '__main__':
    LOG_FILENAME = 'test.log'
    logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,)
    logging.debug('This message should go to the log file')
    try:
       main()
    except:
       logging.exception('Got exception on main handler')
       raise

上面的代码完全可以正常工作。当使用 Flask-Security 和子类 RoleMixin(将 eq 和 ne 函数添加到模型中时，问题就来了。一旦类变成这样:

class Role(db.Model):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(80), unique=True)
    description = db.Column(db.String(255))

    def __init__(self, name, desc):
        self.name = name 
        self.description = desc

    def __repr__(self):
        return '<Role: {}>'.format(str(self.name))


    def __eq__(self, other):
        return (self.name == other or
                self.name == getattr(other, 'name', None))

    def __ne__(self, other):
        return not self.__eq__(other)

我收到以下错误:

ERROR:root:Got exception on main handler
Traceback (most recent call last):
  File "test.py", line 66, in <module>
    main()
  File "test.py", line 53, in main
    adminUser.roles = [adminRole]
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 220, in __set__
    instance_dict(instance), value, None)
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 975, in set
    lambda adapter, i: adapter.adapt_like_to_iterable(i))
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 1010, in _set_iterable
    collections.bulk_replace(new_values, old_collection, new_collection)
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\collections.py", line 782, in bulk_replace
    constants = existing_idset.intersection(values or ())
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\util\_collections.py", line 592, in intersection
    result._members.update(self._working_set(members).intersection(other))
TypeError: unhashable type: 'Role'
DEBUG:root:This message should go to the log file
ERROR:root:Got exception on main handler
Traceback (most recent call last):
  File "test.py", line 66, in <module>
    main()
  File "test.py", line 53, in main
    adminUser.roles = [adminRole]
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 220, in __set__
    instance_dict(instance), value, None)
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 975, in set
    lambda adapter, i: adapter.adapt_like_to_iterable(i))
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\attributes.py", line 1010, in _set_iterable
    collections.bulk_replace(new_values, old_collection, new_collection)
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\orm\collections.py", line 782, in bulk_replace
    constants = existing_idset.intersection(values or ())
  File "C:\Users\ramabodhi\Envs\test\lib\site-packages\sqlalchemy\util\_collections.py", line 592, in intersection
    result._members.update(self._working_set(members).intersection(other))
TypeError: unhashable type: 'Role'

我在 python 3.3 windows 7 上，我所有的包都是最新的。

Answer 1

对此我有一个“解决方案”，但我想确保它是一个可行的解决方案，而不是一个不稳定的 hack。

我意识到将 ne 和 eq 函数添加到类中需要添加 hash 函数，以便模型可散列的。所以现在可以工作了:

class Role(db.Model):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(80), unique=True)
    description = db.Column(db.String(255))

    def __init__(self, name, desc):
        self.name = name 
        self.description = desc

    def __repr__(self):
        return '<Role: {}>'.format(str(self.name))


    def __eq__(self, other):
        return (self.name == other or
                self.name == getattr(other, 'name', None))

    def __ne__(self, other):
        return not self.__eq__(other)

    def __hash__(self):
        return hash(self.name)

让我知道我是否正确地完成了此操作，谢谢!