ValueError: The 'field_name' attribute has no file associated with it - only when updating?

Question

I use DRF and django-storages to upload files to a S3 bucket.

I can create from the admin or from a POST to the API endpoint any new entry with a file.

But for some reason, as soon as I try to update the instance (be it from the admin or from the API endpoint), I get a ValueError that seems to indicate that DRF can't find the file.

But when I use Django's admin or shell, I see that the file has been correctly saved (FieldFile on instance) and that the file has been saved in the bucket.

I don't override anything: not the admin forms, not the serializer's update method, not the view's retrieve method, etc.

I have no idea how that could even be possible.

Any suggestion?

Answer 1

I ended up finding the solution. Somewhere in my code one of the serializer's fields had a to_representation() method that was returning the instance instead of the instance.url. I hope that this will help anyone.