【发布时间】：2020-05-25 07:59:10
【问题描述】：
我的任务是将 Django REST 框架项目从 Django 1.8 升级到 Django 2.x。我已经将整个代码从 python 2.7 移植到 python 3.7 和从 Django 1.8 移植到 2.0.13。我正在使用虚拟环境。
我让它在 python 3.7 和 Django 2.0.13 以及 RESTframework 3.11 上运行，尽管我在尝试创建新对象时遇到了问题。
这是我的问题的追溯：
Traceback (most recent call last):
File "C:\Users\user1\Envs\projpy3\lib\site-packages\django\core\handlers\exception.py", line 35, in inner
response = get_response(request)
File "C:\Users\user1\Envs\projpy3\lib\site-packages\django\core\handlers\base.py", line 128, in _get_response
response = self.process_exception_by_middleware(e, request)
File "C:\Users\user1\Envs\projpy3\lib\site-packages\django\core\handlers\base.py", line 126, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Users\user1\Envs\projpy3\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "C:\Users\user1\projects\proj_py3\rest_framework\viewsets.py", line 114, in view
return self.dispatch(request, *args, **kwargs)
File "C:\Users\user1\projects\proj_py3\rest_framework\views.py", line 505, in dispatch
response = self.handle_exception(exc)
File "C:\Users\user1\projects\proj_py3\rest_framework\views.py", line 465, in handle_exception
self.raise_uncaught_exception(exc)
File "C:\Users\user1\projects\proj_py3\rest_framework\views.py", line 476, in raise_uncaught_exception
raise exc
File "C:\Users\user1\projects\proj_py3\rest_framework\views.py", line 502, in dispatch
response = handler(request, *args, **kwargs)
File "C:\Users\user1\projects\proj_py3\rest_framework\mixins.py", line 18, in create
serializer.is_valid(raise_exception=True)
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 219, in is_valid
self._validated_data = self.run_validation(self.initial_data)
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 418, in run_validation
value = self.to_internal_value(data)
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 471, in to_internal_value
for field in fields:
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 354, in _writable_fields
for field in self.fields.values():
File "C:\Users\user1\Envs\projpy3\lib\site-packages\django\utils\functional.py", line 36, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 348, in fields
for key, value in self.get_fields().items():
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 1027, in get_fields
field_names = self.get_field_names(declared_fields, info)
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 1128, in get_field_names
serializer_class=self.__class__.__name__
AssertionError: The field 'participantIDs' was declared on serializer OrderSerializer, but has not been included in the 'fields' option.
我不明白为什么该异常只发生在新版本的代码中，因为除了版本更新之外，我没有更改 models、serializers 或 views。
这就是有问题的serializer 的样子：
class OrderSerializer(serializers.ModelSerializer):
created_by = ShortPersonSerializer(read_only=True, required=False)
modified_by = ShortPersonSerializer(read_only=True, required=False)
customer = OrderPersonSerializer(required=False, allow_null=True, partial=True)
...
...
participantIDs = serializers.SlugRelatedField(many=True, required=False, allow_null=True, slug_field='id', source='participants', queryset=Person.objects.all())
...
...
class Meta:
model = Order
fields = ('id', 'title','customer',
'customer_copy_id', 'customer_copy_salutation', 'customer_copy_first_name', 'customer_copy_last_name', 'created_at', 'created_by', 'modified_at', 'modified_by')
def create(self, validated_data):
customer_data = validated_data.pop('customer', None)
participants_data = validated_data.pop('participants', None)
if customer_data and customer_data is not None:
validated_data['customer'] = Person(pk=customer_data['id'])
order = Order.objects.create(**validated_data)
if participants_data and participants_data is not None:
setattr(order, 'participants', participants_data) # line 1
order.save() # line 2
...
其他信息： 在检测到这个错误之前，我得到了一个不同的错误，带有以下回溯：
Traceback (most recent call last):
...
...
File "C:\Users\user1\projects\proj_py3\rest_framework\serializers.py", line 204, in save
self.instance = self.create(validated_data)
File "C:\Users\user1\projects\proj_py3\orders\serializers.py", line 90, in create
setattr(order, 'participants', participants_data)
File "C:\Users\user1\Envs\projpy3\lib\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 participants.set() instead.
所以我像这样更改了serializer：
...
...
if participants_data and participants_data is not None:
#setattr(order, 'participants', participants_data) # line 1
order.save() # line 2
order.participants.set(participants_data)
...
自从我这样做后，我得到了AssertionError 而不是TypeError，我不知道如何解决这个问题。当然我把代码改回来了，但我也删除了项目目录中所有编译的文件，我删除了虚拟环境并创建了一个新环境，我在 Windows 上运行了磁盘清理，我什至卸载了 Python37 以安装它再次。总是在中间重新启动。一切都无济于事。
更新：
我将项目的serializers.py 文件中的update 和create 方法与我正在使用的rest_framework 版本中的方法进行了比较：rest_framework/serializers.py on GitHub
我根据较新版本的 Django REST framework 更改了它们（代码是为旧版本开发的）。
我还检查了项目中其他应用程序的所有serializers，我发现，除了相关应用程序orders 之外，所有应用程序的participantsID 都在其Serializer 的@987654342 中具有attribute participantsID @class，以防它应该通过其他的Serializer访问其他App。
在这种情况下，就像 cmets 中建议的那样：AssertionError 一直存在。
除了将attribute 添加到fields 之外别无他法。
【问题讨论】：
标签： django python-3.x django-models django-rest-framework django-serializer