Question

以SQL Alchemy文档中的多对多association_proxy为例，我尝试将其设置为双向工作。我的目标是设置模型，以便在删除关键字时，所有与用户的关联都将从关联表中清除。以下是我正在玩的代码：

from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship, backref

from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))

    keywords = association_proxy('user_keywords', 'keyword')

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

    def __repr__(self):
        return 'User(%s)' % repr(self.name)

class Keyword(Base):
    __tablename__ = 'keyword'
    id = Column(Integer, primary_key=True)
    keyword = Column('keyword', String(64))

    users = association_proxy('keyword_users', 'user')

    def __init__(self, keyword):
        self.keyword = keyword

    def __repr__(self):
        return 'Keyword(%s)' % repr(self.keyword)

class UserKeyword(Base):
    __tablename__ = 'user_keyword'
    user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
    keyword_id = Column(Integer, ForeignKey('keyword.id'), primary_key=True)
    special_key = Column(String(50))

    user = relationship(User,
                        backref=backref('user_keywords',
                                        cascade='all, delete-orphan'))
    keyword = relationship(Keyword,
                           backref=backref('keyword_users',
                                           cascade ='all, delete-orphan'))

    def __init__(self, keyword=None, user=None, special_key=None):
        self.user = user
        self.keyword = keyword
        self.special_key = special_key

    def __repr__(self):
        return "UserKeyword({0}, {1}) Special: {2}".format(user.name,
                                                           keyword.keyword,
                                                           self.special_key)

测试它：

from sqlalchemy import create_engine
engine = create_engine('sqlite://')

from sqlalchemy.orm import sessionmaker
session = sessionmaker()
session.configure(bind=engine)
Base.metadata.create_all(engine)
s = session()

bob = User('Bob')
yay = Keyword('yay')
argh = Keyword('argh')

print("Everything: {0}, {1}, {2}".format(bob, yay, argh))
bob.keywords.append(yay)
print("{0} now has users {1}".format(yay, yay.users))
print("{0} now has users {1}".format(argh, argh.users))
argh.users.append(bob)

以下是我运行时看到的输出：

Players: User('Bob'), Keyword('yay'), Keyword('argh')
Keyword('yay') now has users [User('Bob')]
Keyword('argh') now has users []
Traceback (most recent call last):
  File "assoc_proxy.py", line 78, in <module>
    argh.users.append(bob)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/ext/associationproxy.py", line 595, in append
    item = self._create(value)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/ext/associationproxy.py", line 522, in _create
    return self.creator(value)
  File "<string>", line 4, in __init__
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/state.py", line 196, in _initialize_instance
    return manager.original_init(*mixed[1:], **kwargs)
  File "assoc_proxy.py", line 50, in __init__
    self.keyword = keyword
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 220, in __set__
    instance_dict(instance), value, None)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 780, in set
    value = self.fire_replace_event(state, dict_, value, old, initiator)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 801, in fire_replace_event
    value = fn(state, value, previous, initiator or self._replace_token)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 1101, in emit_backref_from_scalar_set_event
    child_impl = child_state.manager[key].impl
KeyError: 'keyword_users'

在orm/attributes.py的第1101行放置一个断点我看到child_state.manager交替携带keyword_users密钥而不是association_proxy密钥。每个关联表只允许{{1}}一次吗？

Answer 1

我相信它是因为您没有名为keyword_users的表格。它应该是＆＃34; user_keyword＆＃34;，这是您的关联表的名称。

SQL Alchemy关联代理并不是双向工作

1 个答案: