Exception: 'ManyRelatedField' object has no attribute 'Meta'

[jayvdb]

Describe the bug
(line numbers refer to master atm)

Traceback (most recent call last):
  File "./manage.py", line 14, in <module>
    main()
  File "./manage.py", line 10, in main
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.8/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.8/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3.8/site-packages/django/core/management/base.py", line 328, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/lib/python3.8/site-packages/django/core/management/base.py", line 369, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/management/commands/spectacular.py", line 44, in handle
    schema = generator.get_schema(request=None, public=True)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/generators.py", line 152, in get_schema
    paths=self.parse(request, public),
  File "/usr/lib/python3.8/site-packages/drf_spectacular/generators.py", line 132, in parse
    operation = view.schema.get_operation(path, path_regex, method, self.registry)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 76, in get_operation
    operation['responses'] = self._get_response_bodies()
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 790, in _get_response_bodies
    return {'200': self._get_response_for_code(response_serializers)}
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 815, in _get_response_for_code
    component = self.resolve_serializer(serializer, 'response')
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 887, in resolve_serializer
    component.schema = self._map_serializer(serializer, direction)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 560, in _map_serializer
    schema = self._map_basic_serializer(serializer, direction)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 614, in _map_basic_serializer
    schema = self._map_serializer_field(field, direction)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 397, in _map_serializer_field
    schema = self._map_serializer_field(field.child_relation, direction)
  File "/usr/lib/python3.8/site-packages/drf_spectacular/openapi.py", line 409, in _map_serializer_field
    schema = self._map_model_field(field.parent.Meta.model._meta.pk, direction)
AttributeError: 'ManyRelatedField' object has no attribute 'Meta'

To Reproduce
WritableNestedModelSerializer is from https://github.com/beda-software/drf-writable-nested/blob/master/drf_writable_nested/serializers.py , but isnt related afaics.

class Foo(models.Model):
    name = models.CharField(max_length=255)


class Segment(models.Model):
    name = models.CharField(max_length=255)
    foo = models.ForeignKey(
        'Foo',
        on_delete=models.CASCADE,
        related_name='segments',
        null=True,
    )


class SegmentSerializer(WritableNestedModelSerializer):
    class Meta:
        model = Segment
        fields = ('id', 'name', 'foo')


class FooRetrieveSerializer(serializers.ModelSerializer):
    segments = serializers.PrimaryKeyRelatedField(
        read_only=True, many=True)

    class Meta:
        model = Foo
        fields = (
            'id',
            'name',
            'segments',
        )

Expected behavior
Should at least be an 'array of object', but ideally the type&schema of the object is also detected and exposed.

[tfranzel]

i had a quick look. drf_writable_nested is indeed not the issue. i ran the example from the README and no exceptions, no warnings

i fixed the many related issue. it only occurred on read_only fields

@jayvdb please confirm and close.

[jayvdb]

Works well; thanks