【发布时间】：2019-03-02 03:46:30
【问题描述】：
我有一个模型 UserSong，它有两个 m2m 字段，模型类型为 Genre 和 Language
class UserSong(models.Model):
title = models.CharField(max_length=100)
song_file = models.FileField(upload_to=user_song_directory_path, validators=[validate_audio_file_extension])
genre = models.ManyToManyField(Genre)
language = models.ManyToManyField(Language)
流派类是
class Genre(models.Model):
name = models.CharField(max_length=255)
created_date = models.DateTimeField(auto_now_add=True)
updated_date = models.DateTimeField(auto_now=True)
status = models.BooleanField(default=False)
语言类是
class Language(models.Model):
name = models.CharField(max_length=255)
created_date = models.DateTimeField(auto_now_add=True)
updated_date = models.DateTimeField(auto_now=True)
status = models.BooleanField(default=False)
我正在尝试将 UserSong 对象中的 m2m 字段添加为
genre_name_list = Genre.objects.filter(name__in=self.cleaned_data['genre'].values_list('name',flat=True))
# instance.genre.add(*genre_name_list)
instance.genre.set(genre_name_list)
language_name_list = Language.objects.filter(name__in=self.cleaned_data['language'].values_list('name',flat=True))
# instance.language.add(*language_name_list)
instance.language.set(language_name_list)
这里的问题是，m2m 表正在更新，但 Django 仍然给我错误Direct assignment to the forward side of a many-to-many set is prohibited. Use language.set() instead.
堆栈跟踪
form.cleaned_data['genre'] <class 'genre.models.Genre'>
artist received is <QuerySet [<UserProfile: Pragya Nagpal>]>
Internal Server Error: /users/5/25/edit_music
Traceback (most recent call last):
File "/usr/lib/python3.5/site-packages/django/core/handlers/exception.py", line 35, in inner
response = get_response(request)
File "/usr/lib/python3.5/site-packages/django/core/handlers/base.py", line 128, in _get_response
response = self.process_exception_by_middleware(e, request)
File "/usr/lib/python3.5/site-packages/django/core/handlers/base.py", line 126, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/usr/lib/python3.5/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
return view_func(request, *args, **kwargs)
File "/usr/lib/python3.5/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
return view_func(request, *args, **kwargs)
File "/root/new_songdew_store/songdewUser/views.py", line 833, in add_edit_music
status=model_instance.status)
File "/usr/lib/python3.5/site-packages/django/db/models/manager.py", line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/usr/lib/python3.5/site-packages/django/db/models/query.py", line 415, in create
obj = self.model(**kwargs)
File "/usr/lib/python3.5/site-packages/django/db/models/base.py", line 490, in __init__
_setattr(self, prop, kwargs[prop])
File "/usr/lib/python3.5/site-packages/django/db/models/fields/related_descriptors.py", line 509, in __set__
% self._get_set_deprecation_msg_params(),
TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use language.set() instead.
【问题讨论】：
-
您使用
.set(...)的代码看起来没问题。您确定是导致错误的代码吗？确保您已保存/部署该代码并重新启动服务器，并在您的问题中包含完整的回溯。 -
@Alasdair ，我很难找到这个。正如您所说，我认为它可以正常工作，因为我有类似的模型
UserVideo和Album，它们也一样。奇怪的是，这是在开发服务器中，并且经过了足够公平的测试。但是现在只有这个模型会抛出错误，而不是其他模型。 P.S 错误use language.set() instead有时会随着use genre.set() instead而变化。 -
您问题中的
form.cleaned_data表明该错误在您保存表单时较早发生。回溯将准确显示错误发生的位置。 -
@Alasdair 我仔细检查了它。忽略
self.cleaned_data['genre']类型（它已经是一个查询集，所以使用set(self.cleaned_data['genre'])也可以），stacktrace 不会提供任何有用的信息。 -
天哪，m2m 表仍在更新中。有趣到可以大声哭泣