我正试图使用序列化程序在视图中创建一个对象。然而，我的一个对象遇到了一个烦人的问题：
这就是我创建对象的方式：
editObject = Question_edit(
question=question,
description='CREATE Question: %s' % question.text,
editor=user,
notes=question.notes
)
print(editObject) # return 'Question_edit object (None)'
serializer = Question_editSerializer(editObject)
json = JSONRenderer().render(serializer.data)
stream = io.BytesIO(json)
data = JSONParser().parse(stream)
serializer = Question_editSerializer(data=data)
serializer.is_valid(raise_exception=True)
serializer.save()
这是我的Question_editSerializer:
class Question_editSerializer(serializers.ModelSerializer):
time_since_edit = serializers.SerializerMethodField()
class Meta:
model = Question_edit
fields = "__all__"
def get_time_since_edit(self, object):
date_edit = object.date
time_delta = timesince(date_edit, timezone.now())
return time_delta
def create(self, validated_data):
return Question_edit.objects.create(**validated_data)
我的Question_edit模型：
class Question_edit(models.Model):
date = models.DateTimeField(auto_now_add=True)
question = models.ForeignKey(Question, on_delete=models.CASCADE)
description = models.TextField(max_length=500)
editor = models.ForeignKey(
CustomUser, on_delete=models.SET_NULL, null=True)
notes = models.TextField(max_length=500, blank=True, null=True)
由于在上面的第一段代码中尝试使用序列化程序创建对象，我得到了以下错误：
File "/foodbook24-api/questions/api/serializers.py", line 44, in get_time_since_edit
time_delta = timesince(date_edit, timezone.now())
File "/usr/local/lib/python3.8/site-packages/django/utils/timesince.py", line 49, in timesince
d = datetime.datetime(d.year, d.month, d.day)
Exception Type: AttributeError at /api/questionnaires/
Exception Value: 'NoneType' object has no attribute 'year'
完整追溯：
Environment:
Request Method: POST
Request URL: http://localhost:8000/api/questionnaires/
Django Version: 3.1.3
Python Version: 3.8.6
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'django.contrib.sites',
'rest_framework',
'rest_framework.authtoken',
'drfpasswordless',
'allauth',
'allauth.account',
'allauth.socialaccount',
'rest_auth',
'rest_auth.registration',
'django_filters',
'corsheaders',
'surveys',
'questionnaire',
'questions',
'users',
'foods',
'utilities']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'corsheaders.middleware.CorsMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware']
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "/usr/local/lib/python3.8/site-packages/django/core/handlers/base.py", line 179, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/usr/local/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "/usr/local/lib/python3.8/site-packages/django/views/generic/base.py", line 70, in view
return self.dispatch(request, *args, **kwargs)
File "/usr/local/lib/python3.8/site-packages/rest_framework/views.py", line 509, in dispatch
response = self.handle_exception(exc)
File "/usr/local/lib/python3.8/site-packages/rest_framework/views.py", line 469, in handle_exception
self.raise_uncaught_exception(exc)
File "/usr/local/lib/python3.8/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
raise exc
File "/usr/local/lib/python3.8/site-packages/rest_framework/views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "/usr/local/lib/python3.8/site-packages/rest_framework/generics.py", line 242, in post
return self.create(request, *args, **kwargs)
File "/foodbook24-api/questionnaire/api/views.py", line 184, in create
return self.elaborateClientPOSTRequest(request)
File "/foodbook24-api/questionnaire/api/views.py", line 114, in elaborateClientPOSTRequest
self.create_question_edit_record(questionObject, request)
File "/foodbook24-api/questionnaire/api/views.py", line 85, in create_question_edit_record
json = JSONRenderer().render(serializer.data)
File "/usr/local/lib/python3.8/site-packages/rest_framework/serializers.py", line 548, in data
ret = super().data
File "/usr/local/lib/python3.8/site-packages/rest_framework/serializers.py", line 246, in data
self._data = self.to_representation(self.instance)
File "/usr/local/lib/python3.8/site-packages/rest_framework/serializers.py", line 515, in to_representation
ret[field.field_name] = field.to_representation(attribute)
File "/usr/local/lib/python3.8/site-packages/rest_framework/fields.py", line 1870, in to_representation
return method(value)
File "/foodbook24-api/questions/api/serializers.py", line 44, in get_time_since_edit
time_delta = timesince(date_edit, timezone.now())
File "/usr/local/lib/python3.8/site-packages/django/utils/timesince.py", line 49, in timesince
d = datetime.datetime(d.year, d.month, d.day)
Exception Type: AttributeError at /api/questionnaires/
Exception Value: 'NoneType' object has no attribute 'year'
我在这里错过了什么？
在以下代码中，您忘记保存editObject:
editObject = Question_edit(
question=question,
description='CREATE Question: %s' % question.text,
editor=user,
notes=question.notes
)
print(editObject) # return 'Question_edit object (None)'
serializer = Question_editSerializer(editObject)
json = JSONRenderer().render(serializer.data)
stream = io.BytesIO(json)
data = JSONParser().parse(stream)
serializer = Question_editSerializer(data=data)
serializer.is_valid(raise_exception=True)
serializer.save()
只有当对象保存到数据库时，Django才会计算日期并将其存储在editObject.date中。由于没有发生这种情况，一旦您访问了上面的serializer.data，您的get_time_since_edit()方法就会尝试计算None和timezone.now()之间的差，从而导致错误'NoneType' object has no attribute 'year'
您可以通过将上述代码更改为以下代码来解决此问题：
editObject = Question_edit(
question=question,
description='CREATE Question: %s' % question.text,
editor=user,
notes=question.notes
)
editObject.save() # This will populate the `date` attribute with the current date/time
serializer = Question_editSerializer(editObject)
json = JSONRenderer().render(serializer.data)
stream = io.BytesIO(json)
data = JSONParser().parse(stream)
serializer = Question_editSerializer(data=data)
serializer.is_valid(raise_exception=True)
serializer.save()