Determine if a field is async or not by the presence of ato_represent…

…ation.

Don't hard-code the list of DRF_FIELDS--this was missing things like
SerializerMethodField, ManyRelatedField, and ReadOnlyField.

adrf/serializers.py

@@ -1,3 +1,4 @@
+import asyncio
 import traceback
 from collections import OrderedDict
 
@@ -15,14 +16,6 @@
 from rest_framework.serializers import Serializer as DRFSerializer
 from rest_framework.utils.serializer_helpers import ReturnDict, ReturnList
 
-# NOTE This is the list of fields defined by DRF for which we need to call to_rapresentation.
-DRF_FIELDS = list(DRFModelSerializer.serializer_field_mapping.values()) + [
-    DRFModelSerializer.serializer_related_field,
-    DRFModelSerializer.serializer_related_to_field,
-    DRFModelSerializer.serializer_url_field,
-    DRFModelSerializer.serializer_choice_field,
-]
-
 
 class BaseSerializer(DRFBaseSerializer):
     """
@@ -159,10 +152,10 @@ async def ato_representation(self, instance):
             if check_for_none is None:
                 ret[field.field_name] = None
             else:
-                if type(field) in DRF_FIELDS:
-                    repr = field.to_representation(attribute)
-                else:
+                if asyncio.iscoroutinefunction(getattr(field, "ato_representation", None)):
                     repr = await field.ato_representation(attribute)
+                else:
+                    repr = field.to_representation(attribute)
 
                 ret[field.field_name] = repr