PostUpdateAPIView.py

class UpdatePostAPIView(APIView):

    permission_classes = (IsAuthenticated,)
    parser_classes = (MultiPartParser, FormParser)

    @staticmethod
    def get(request: WSGIRequest, pk: int) -> Response:
        try:
            # Solves the problem of checking whether user owns post referenced.
            post = Post.objects.filter(user=request.user).get(pk=pk)
        except Post.DoesNotExist:
            return Response({'detail': 'Not found.'}, status=status.HTTP_404_NOT_FOUND)
        else:
            return Response(PostSerializer(post).data)

    @staticmethod
    def put(request: WSGIRequest, pk: int) -> Response:

        try:
            # Solves the problem of checking whether user owns post referenced.
            post = Post.objects.filter(user=request.user).get(pk=pk)
        except Post.DoesNotExist:
            return Response({'detail': 'Not found.'}, status=status.HTTP_404_NOT_FOUND)

        # Provides a list of ids for images to be deleted.
        to_delete = set(map(int, request.POST.getlist('to_delete')))

        # Provides a list of additional (or replacement) images to be uploaded.
        additional_images = request.FILES.getlist('images')

        post_images = post.images.all()
        post_images_count = post_images.count()

        final_images_count = post_images_count - len(to_delete) + len(additional_images)

        if final_images_count > 5 or final_images_count <= 0:
            # Check if the difference between the number of images requested to be deleted
            # and the total number of images currently in post added with the total number
            # new images to be uploaded lies between 0 and 5.
            return Response(
                {'detail': 'Cannot have post with 0 images.'},
                status=status.HTTP_400_BAD_REQUEST,
            )
        elif to_delete.issubset(set(post_images.values_list('pk', flat=True))):
            # Default case if everything goes right since only two situations can evaluate
            # the above clause to be true -
            #   1. Either no new images were provided and thus an empty set will always be
            #      a subset to all the images already existing in the post OR
            #   2. The ids that were provided in to_delete were valid ids that belong to the
            #      id list of the images reversely to the post.

            # Bulk delete images if any.
            post_images.filter(id__in=to_delete).delete()

            # Upload images if any.
            for image in additional_images:
                image_serializer = ImageSerializer(
                    data={'file': image, 'post': post.id}
                )
                if image_serializer.is_valid():
                    image_serializer.save()
                else:
                    return Response(
                        {'error': 'Invalid image data.'},
                        status=status.HTTP_409_CONFLICT,
                    )
            else:
                # Everything has gone right so far and a sanitary update of caption is left.
                if request.POST.get('caption', False):
                    post.caption = request.POST['caption']
                    post.save()
                return Response({'success': 'Updated.'}, status=status.HTTP_200_OK)
        else:
            return Response({'error': 'Not found.'}, status=status.HTTP_404_NOT_FOUND)