is_patched_serializer fails with DictField

[mblayman]

Describe the bug
My team has a list endpoint that returns a dictionary values that are generated by methods that aren't serializers. We'd like to document at least that this endpoint returns a list of objects. I tried adding the following extend_schema:

    @extend_schema(
        responses=serializers.ListSerializer(child=serializers.DictField()),
    )
    def get(self, request: Request, *args: Any, **kwargs: Any) -> Response:
        data = # complex code to produce list of dicts here.
        return Response(data, status=200)

drf-spectacular raised the following exception:

Traceback (most recent call last):
  File "manage.py", line 11, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/management/commands/spectacular.py", line 50, in handle
    schema = generator.get_schema(request=None, public=True)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py", line 230, in get_schema
    paths=self.parse(request, public),
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py", line 207, in parse
    operation = view.schema.get_operation(path, path_regex, method, self.registry)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/utils.py", line 222, in get_operation
    return super().get_operation(path, path_regex, method, registry)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 83, in get_operation
    operation['responses'] = self._get_response_bodies()
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 975, in _get_response_bodies
    return {'200': self._get_response_for_code(response_serializers, '200')}
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 1036, in _get_response_for_code
    paginated_name = f'Paginated{self._get_serializer_name(serializer, "response")}List'
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 1119, in _get_serializer_name
    return self._get_serializer_name(serializer.child, direction)
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py", line 1126, in _get_serializer_name
    if is_patched_serializer(serializer, direction):
  File "/usr/local/lib/python3.7/site-packages/drf_spectacular/plumbing.py", line 101, in is_patched_serializer
    and serializer.partial
AttributeError: 'DictField' object has no attribute 'partial'

Expected behavior

Since this should be a valid serializer (test proving that is below), I'd expect the is_patched_serializer to handle a DictField.

    def test_list_serializer(self):
        from rest_framework.serializers import DictField, ListSerializer

        class MyListSerializer(ListSerializer):
            child = DictField()

        my_list = [{}, {'a': 'b'}]

        serializer = MyListSerializer(my_list)
        assert serializer.data == [{}, {'a': 'b'}]

[tfranzel]

hi. i cannot reproduce this issue. also this does not look like the newest version. the following example has worked for me.

def test_list_dict_field(no_warnings):

    class XAPIView(APIView):
        @extend_schema(responses=serializers.ListSerializer(child=serializers.DictField()))
        def get(self, request):
            pass  # pragma: no cover

    schema = generate_schema('x', view=XAPIView)

[mblayman]

Thanks for the example. That helped me write the reproduction test. The problem manifests itself for a ListAPIView. I was able to get a reproduction with:

    def test_list_dict_field(no_warnings):
        from django.urls import path
        from drf_spectacular.generators import SchemaGenerator
        from drf_spectacular.utils import extend_schema
        from drf_spectacular.validation import validate_schema
        from rest_framework.generics import ListAPIView
        from rest_framework.serializers import DictField, ListSerializer

        class XAPIView(ListAPIView):
            @extend_schema(responses=ListSerializer(child=DictField()))
            def get(self, request):
                pass  # pragma: no cover

        generator = SchemaGenerator(patterns=[path('v1/x', XAPIView.as_view())])
        schema = generator.get_schema(request=None, public=True)
        validate_schema(schema)

[tfranzel]

hey @mblayman,

i still cannot reproduce the issue. at least on the current master. your snippet generates without a problem and with the expected output. i just pasted it in test_regressions.py and it ran like that.

are you using the most recent version there? although i cannot remember any fixes there in the past couple of releases.

[mblayman]

We weren't when I reported this. I can try again on 0.17.0 (hopefully later today) and report if I can replicate the issue still.

[mblayman]

I ran this same test that I have above with 0.17.0 and it still fails for me. Is there anything else I could provide to help replicate this?

    def test_list_dict_field(no_warnings):
        from django.urls import path
        from drf_spectacular.generators import SchemaGenerator
        from drf_spectacular.utils import extend_schema
        from drf_spectacular.validation import validate_schema
        from rest_framework.generics import ListAPIView
        from rest_framework.serializers import DictField, ListSerializer
    
        class XAPIView(ListAPIView):
            @extend_schema(responses=ListSerializer(child=DictField()))
            def get(self, request):
                pass  # pragma: no cover
    
        generator = SchemaGenerator(patterns=[path('v1/x', XAPIView.as_view())])
>       schema = generator.get_schema(request=None, public=True)

bhps/tests/test_views.py:1952: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py:257: in get_schema
    paths=self.parse(request, public),
/usr/local/lib/python3.7/site-packages/drf_spectacular/generators.py:232: in parse
    path, path_regex, path_prefix, method, self.registry
/usr/local/lib/python3.7/site-packages/drf_spectacular/utils.py:274: in get_operation
    return super().get_operation(path, path_regex, path_prefix, method, registry)
/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:84: in get_operation
    operation['responses'] = self._get_response_bodies()
/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:1001: in _get_response_bodies
    return {'200': self._get_response_for_code(response_serializers, '200')}
/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:1075: in _get_response_for_code
    paginated_name = f'Paginated{self._get_serializer_name(serializer, "response")}List'
/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:1155: in _get_serializer_name
    return self._get_serializer_name(serializer.child, direction)
/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:1162: in _get_serializer_name
    if is_patched_serializer(serializer, direction):
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

serializer = DictField(), direction = 'response'

    def is_patched_serializer(serializer, direction):
        return bool(
            spectacular_settings.COMPONENT_SPLIT_PATCH
>           and serializer.partial
            and not serializer.read_only
            and not (spectacular_settings.COMPONENT_SPLIT_REQUEST and direction == 'response')
        )
E       AttributeError: 'DictField' object has no attribute 'partial'

/usr/local/lib/python3.7/site-packages/drf_spectacular/plumbing.py:97: AttributeError

[tfranzel]

/usr/local/lib/python3.7/site-packages/drf_spectacular/openapi.py:1075: in _get_response_for_code
paginated_name = f'Paginated{self._get_serializer_name(serializer, "response")}List'

the stacktrace contains a line that is only reached by using pagination. Since you have no pagination class in your example, i have to assume that you have a global default setting. with a added pagination class i can reproduce the error.

[mblayman]

That's right. We're using the LimitOffsetPagination.

REST_FRAMEWORK = {
    'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.LimitOffsetPagination',
    ...
}

[tfranzel]

that was a small but important detail

[tfranzel]

so i analyzed this issue. it's definitely an edge case. in theory this is not supported.

theoretically the more correct version would have been serializers.ListField(child=serializers.CharField()), which we would have rejected with a warning. that is because putting fields in responses= is generally not supported. you circumvented that by using ListSerializer instead of ListField. those two are very close and DRF is intentionally fuzzy there.

on the other hand i can see the need for this. responses= takes a heap of things, just not fields and you cannot define a list of "things" with the basic types and OpenApiTypes.

since there is no other way expressing what you need and its a very reasonable ask, i think it's acceptable to be lenient here and "do the right thing" even though it would be technically incorrect.

[tfranzel]

this should fix it. i also noticed that we support this for unpaginated endpoints. so having parity again is another benefit.

[mblayman]

Thank you for digging into this and fixing it up. I appreciate your attention to detail.

[tfranzel]

closing this issue for now. feel free to comment if anything is missing or not working and we will follow-up.