Improve error handling when accessing request.data in get_serializer_class

[DeadLemon]

Hi there!
I'm trying to specify different serializers depend on user type or request data.

class UserViewSet(serializers.ModelSerializer):
    ...
    def get_serializer_class(self):
        serializers_map = {}
        if self.request.user.is_authenticated:
            pass
        else:
            serializers_map.update({'create': serializers.CreateSerializerForAnonymousUser})
        return serializers_map.get(view.action, None)

So, I get an error:
[{'detail': 'JSON parse error - Expecting value: line 1 column 1 (char 0)', 'source': {'pointer': '/data'}, 'status': '400'}]
Here is my test code:

class UserEndpointCreateTest(APITestCase):
    def setUp(self):
        self.path = reverse('user-list')
        self.data = {
            'data': {
                'type': format_resource_type('user'),
                'attributes': {
                    'phone_number': '+79000000001',
                    'password': 'password'
                }
            }
        }

    def test_anonymous_user(self):
        response = self.client.post(reverse('user-list'), json.dumps(self.data), content_type='application/vnd.api+json')
        print(response.data)

Also, I tried this code with default rest_framework serializer, renderers and parsers - it works properly. Note that this problem exposes only when I'm trying to access request.user or request.data

[sliverc]

Could it be that this is a simply test setup issue and would be solved with changes of #396?

[sliverc]

As there hasn't been any feedback I assume this has been solved with changes in #396

Closing but if there is still a question concerning this issue please comment and we can reopen.

[aradbar]

@sliverc I just ran into this issue as well. From a quick look it seems that JSONParser uses get_serializer_class() as part of trying to determine the resource_name. So when the view implements a custom get_serializer_class that includes a reference to request.data this error occurs.

https://github.com/django-json-api/django-rest-framework-json-api/blob/master/rest_framework_json_api/parsers.py#L121
https://github.com/django-json-api/django-rest-framework-json-api/blob/master/rest_framework_json_api/utils.py#L55

[sliverc]

@aradbar Thanks for the additional information and the pointer. I see that accessing request.data in get_serializer_class causes issues although in the initial example of this issue it actually accesses request.user which in my opinion should work.

Anyhow I do not really see how this can be fixed while DJA continues supporting polymorphic serializers seamlessly. Or do you have any ideas?

A workaround which would work would be to define resource_name on the view which overwrites get_serializer_class. This might be good enough for affected users who might stumble upon this issue.

[aradbar]

@sliverc I agree with what you said but I think it's problematic for DJA to use get_serializer_class internally, as it is a DRF hook and can contain unexpected logic.
I would expect DJA to use serializer_class like it does here:

django-rest-framework-json-api/rest_framework_json_api/parsers.py

Line 143 in 2033bc5

serializer_class = getattr(view, 'serializer_class', None)

With an assertion error that tells the user do define resource_name in case serializer_class is not defined

[sliverc]

@aradbar I think this makes the situation worse for users not using polymorphic serializers as with such a change every user of DJA which has get_serializer_class overwritten will have an error. In the current state only users which access request.data within get_serializer_class do and I would argue accessing request.data is rare as it doesn't sound very resty to me.

Anyhow thinking about it again the error message is confusing. I think it would be good to improve it so states something in the lines that an parser error occurred while calling get_serializer_class as most likely request.data has been access and that overwriting resource_name could solve this issue.

So reoping this issue and marking so this can be addressed.