Nested objects not deserialized when many=True during PUT requests

[dulacp]

The error is raised when I'm submitting the following request thanks to the httpie command on an existing album :

$ http -v PUT http://localhost:8000/api/albums/2/ songs:='[{"title":"Imagine"}]'

Whereas, a POST request is working perfectly, like this one

$ http -v POST http://localhost:8000/api/albums/ title="Let It Be" songs:='[{"title":"Dig a Pony"}]'

I've track down the error to be that the variable instance is an instance of django.db.models.fields.related.RelatedManager that is not judged as an iterable object by default... it's only iterable after calling the all method.

Whereas, for the POST request, this same variable instance is set to None.

I didn't find a fix for it yet, but I'll make a PR as soon as I do.

---

version of django-rest-framework: 2.3.6

My Serializers

class SongSerializer(serializers.ModelSerializer):
    class Meta:
        model = Song

class AlbumSerializer(serializers.ModelSerializer):
    songs = SongSerializer(many=True)
    class Meta:
        model = Album

My Views

class AlbumViewSet(viewsets.ModelViewSet):
    model = Album
    serializer_class = AlbumSerializer

Full error traceback

Traceback (most recent call last):
  File "/MyVirtualEnv/lib/python2.7/site-packages/django/core/handlers/base.py", line 115, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/viewsets.py", line 78, in view
    return self.dispatch(request, *args, **kwargs)
  File "/MyVirtualEnv/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 77, in wrapped_view
    return view_func(*args, **kwargs)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/views.py", line 327, in dispatch
    response = self.handle_exception(exc)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/views.py", line 324, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Users/peteralaoui/Sites/Carousel/Code/carousel-website-api/carousel/apps/api/views.py", line 89, in update
    return super(CardViewSet, self).update(request, pk=pk)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/mixins.py", line 129, in update
    if serializer.is_valid():
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 480, in is_valid
    return not self.errors
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 472, in errors
    ret = self.from_native(data, files)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 868, in from_native
    instance = super(ModelSerializer, self).from_native(data, files)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 318, in from_native
    attrs = self.restore_fields(data, files)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 244, in restore_fields
    field.field_from_native(data, files, field_name, reverted_data)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 397, in field_from_native
    serializer = self.__class__(**kwargs)
  File "/MyVirtualEnv/lib/python2.7/site-packages/rest_framework/serializers.py", line 168, in __init__
    raise ValueError('instance should be a queryset or other iterable with many=True')
ValueError: instance should be a queryset or other iterable with many=True

[maspwr]

I believe this is fixed with #750. Can you perhaps take a look and verify?

[maspwr]

Specifically this line https://github.com/tomchristie/django-rest-framework/pull/750/files#L1R383.

[dulacp]

Thanks @maspwr the line you've pointed me to seems perfect, I will try your pull-request right now and let you know of the result.

[maspwr]

Great! Let me know if you have any issues. Also, if you find any problems with that pull request, please do respond to it and I'll try to address them. It's great to get some more testing on it before it gets merged.

[dulacp]

That's working ! Great work :)

When I do the PUT request mentioned above in my initial error

$ http -v PUT http://localhost:8000/api/albums/2/ songs:='[{"title":"Imagine"}]'

I'm getting a "Cannot create a new item, only existing items may be updated.", so that's the kind of the fair response I should have expected. So it's working for me !

---

Then, when I'm trying to update an exisiting item with this request

$ http -v PUT http://localhost:8000/api/albums/2/ songs:='[{"id":6, "title":"Imagine version 2"}]'

That is perfectly working!

---

The last test I've to run, is with the new routing feature of django-rest-framework, I've to try this request

$ http -v POST http://localhost:8000/api/albums/2/songs/ title="Dig a Pony"

But that's out of the scope of the nested objects pull-request

Well to sum up, I will close my issue since it's fixed by #750