升级到Django 1.3后ManyToMany出现FieldError

Question

我刚刚把Django更新到了1.3版本，遇到了一个奇怪的错误。之前在1.2.7版本上能正常工作的代码，现在出现了以下错误。

FieldError: Cannot resolve keyword 'email_config_set' into field. Choices are: id, name, site, type

奇怪的是，email_config_set是一个多对多字段的相关名称。我不明白为什么Django会试图把它解析成一个字段。

这个错误发生在Django的内部深处：

Traceback (most recent call last):
  File "./core/driver.py", line 268, in run
    self.init_norm()
  File "./driver/emailevent/background.py", line 130, in init_norm
    self.load_config()
  File "./driver/emailevent/background.py", line 71, in load_config
    events = list(config.events.select_related())
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/manager.py", line 168, in select_related
    return self.get_query_set().select_related(*args, **kwargs)
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/fields/related.py", line 497, in get_query_set
    return superclass.get_query_set(self).using(db)._next_is_sticky().filter(**(self.core_filters))
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/query.py", line 550, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/query.py", line 568, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/sql/query.py", line 1194, in add_q
    can_reuse=used_aliases, force_having=force_having)
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/sql/query.py", line 1069, in add_filter
    negate=negate, process_extras=process_extras)
  File "/usr/local/lib/python2.6/site-packages/Django-1.3.1-py2.6.egg/django/db/models/sql/query.py", line 1260, in setup_joins
    "Choices are: %s" % (name, ", ".join(names)))
FieldError: Cannot resolve keyword 'email_config_set' into field. Choices are: id, name, site, type

如果有任何建议或提示，我都会很感激。

Answer 1

这个问题是因为动态模型和它们的创建顺序引起的。具体来说，有些模型是在其他模型之后动态创建的，这些模型在填充_meta缓存时还没有定义，因此就会导致错误。清除缓存或者改变创建顺序可以解决这个问题。

另见 https://groups.google.com/d/msg/django-users/RJlV5_ribZk/P6tv4QlJN4EJ