failing PUT test but otherwise successful polymorphism due to discrepancy between DJA and DRF ModelViewSet

Author: n2ygk

example/views.py

@@ -2,6 +2,7 @@
 import rest_framework.parsers
 import rest_framework.renderers
 from django_filters import rest_framework as filters
+from rest_framework import viewsets
 from rest_framework.filters import SearchFilter
 
 import rest_framework_json_api.metadata
@@ -11,7 +12,7 @@
 from rest_framework_json_api.filters import OrderingFilter, QueryParameterValidationFilter
 from rest_framework_json_api.pagination import JsonApiPageNumberPagination
 from rest_framework_json_api.utils import format_drf_errors
-from rest_framework_json_api.views import ModelViewSet, RelationshipView
+from rest_framework_json_api.views import ModelViewSet, PreloadIncludesMixin, RelationshipView
 
 from example.models import Author, Blog, Comment, Company, Entry, Project, ProjectType
 from example.serializers import (
@@ -199,7 +200,7 @@ def get_queryset(self, *args, **kwargs):
         return super(CommentViewSet, self).get_queryset()
 
 
-class CompanyViewset(ModelViewSet):
+class CompanyViewset(PreloadIncludesMixin, viewsets.ModelViewSet):
     queryset = Company.objects.all()
     serializer_class = CompanySerializer
     prefetch_for_includes = {