django-yasg Polymorphic Serializer Inspector

utils.py

### settings
"""
SWAGGER_SETTINGS = {
  ...
  'DEFAULT_FIELD_INSPECTORS': [
    'project.utils.PolymorphicSerializerInspector',
    'drf_yasg.inspectors.CamelCaseJSONFilter',
    'drf_yasg.inspectors.ReferencingSerializerInspector',
    'drf_yasg.inspectors.RelatedFieldInspector',
    'drf_yasg.inspectors.ChoiceFieldInspector',
    'drf_yasg.inspectors.FileFieldInspector',
    'drf_yasg.inspectors.DictFieldInspector',
    'drf_yasg.inspectors.JSONFieldInspector',
    'drf_yasg.inspectors.HiddenFieldInspector',
    'drf_yasg.inspectors.RecursiveFieldInspector',
    'drf_yasg.inspectors.SerializerMethodFieldInspector',
    'drf_yasg.inspectors.SimpleFieldInspector',
    'drf_yasg.inspectors.StringDefaultFieldInspector',
  ],
  ...
}
"""

from drf_yasg.inspectors import SerializerInspector
from drf_yasg import openapi
from rest_polymorphic.serializers import PolymorphicSerializer
import re


class PolymorphicSerializerInspector(SerializerInspector):
  def _get_definition_name(self, ref):
      m = re.search(r"#/definitions/(?P<definition_name>\w+)", ref)
      return m.group('definition_name')

  def _get_schema_ref(self, serializer):
      schema_ref = self.probe_inspectors(
          self.field_inspectors, 'get_schema', serializer, {
              'field_inspectors': self.field_inspectors
          }
      )
      return schema_ref

  def _get_schema(self, serializer, schema_ref=None):
      if schema_ref is None:
          schema_ref = self._get_schema_ref(serializer)
      schema = openapi.resolve_ref(schema_ref, self.components)
      return schema

  def process_result(self, result, method_name, obj, **kwargs):
    if isinstance(result, openapi.Schema.OR_REF) and issubclass(obj.__class__,
                                                                PolymorphicSerializer):
      definitions = self.components._objects['definitions']
      definition_name = self._get_definition_name(result['$ref'])
      definitions.pop(definition_name, None)

      base_model_name = obj.base_serializer_class.Meta.model._meta.object_name
      base_ref = '#/definitions/{}'.format(base_model_name)
      if base_model_name not in definitions:
        schema = self._get_schema(obj.base_serializer_class())
        schema['discriminator'] = obj.resource_type_field_name
        schema['required'] = schema.setdefault('required', []) + [obj.resource_type_field_name]
        schema['properties'][obj.resource_type_field_name] = openapi.Schema(
          title=obj.resource_type_field_name, type=openapi.TYPE_STRING,
          enum=[obj.to_resource_type(model) for model in obj.model_serializer_mapping.keys()]
        )
        definitions[base_model_name] = schema

      for model, serializer in obj.model_serializer_mapping.items():
        if serializer is None:
          serializer = obj.base_serializer_class()
        discriminator = model._meta.object_name
        if discriminator not in definitions:
          schema_ref = self._get_schema_ref(serializer)
          all_of = [
            {'$ref': base_ref}
          ]
          if schema_ref['$ref'] != base_ref:
            model_schema = self._get_schema(serializer, schema_ref=schema_ref)
            # Avoid doubling up on properties from base serializer
            for prop in definitions.get(base_model_name, {}).get('properties'):
              model_schema['properties'].pop(prop, None)
            all_of.append(model_schema)
          definitions[discriminator] = openapi.Schema(
            type=openapi.TYPE_OBJECT,
            allOf=all_of
          )
      result['$ref'] = base_ref
    return result

Thanks a lot 👌 Improved things a lot for me 🥳

Needed to add import re and the property base_serializer_class to my PolymorphicSerializer. Afterwards the generated documentation did a leap forward...

Really helpful piece of code! Thank you!