One to Many objects updated but changes not reflected in the response when using prefetch_related

[gkpo]

For the sake of simplicity, I'll be talking about Posts and Comments event though my models are different ones. This could be a duplicate of #1556, but it's closed and is about an outdated version of DRF.

Steps to reproduce

I created a PostViewSet and redefined the get_queryset method.

def get_queryset(self):
    queryset = Post.objects.prefetch_related('comments')
    return queryset

I'm trying to update the full Post object. For this I send a PUT request containing the post with its comments. I had to redefine the update method in the serializer to handle nested comments.

Expected behavior

The new comments are added to the post, the updated post is served back in the http response. With all updated fields, and updated comments.

Actual behavior

The new comments are indeed added to the post, but the returned item in the http response is the one BEFORE it was updated. Removing the prefetch_related solves the issue but I need it.

[xordoquy]

It's rather a duplicate of #2442.
Using prefetch requires the developer to override the returned value.

[tomchristie]

Bumped the priority of #2442