Assert fields in exclude are model fields

[maryokhin]

I guess something changed in the way DRF 3 includes default many-to-many fields for ModelSerializer, because as soon as I upgraded I got this unhelpful stack-trace:

Traceback:
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/django/core/handlers/base.py" in get_response
  111.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/django/views/decorators/csrf.py" in wrapped_view
  57.         return view_func(*args, **kwargs)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/viewsets.py" in view
  85.             return self.dispatch(request, *args, **kwargs)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/views.py" in dispatch
  407.             response = self.handle_exception(exc)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/views.py" in dispatch
  404.             response = handler(request, *args, **kwargs)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/mixins.py" in list
  46.         return Response(serializer.data)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in data
  422.         ret = super(Serializer, self).data
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in data
  177.                 self._data = self.to_representation(self.instance)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in to_representation
  391.                 ret[field.field_name] = field.to_representation(attribute)
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in to_representation
  524.             self.child.to_representation(item) for item in iterable
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in <listcomp>
  524.             self.child.to_representation(item) for item in iterable
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in to_representation
  384.         fields = [field for field in self.fields.values() if not field.write_only]
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in fields
  277.             for key, value in self.get_fields().items():
File "/Users/maryokhin/.virtualenvs/backend-drf3/lib/python3.4/site-packages/rest_framework/serializers.py" in get_fields
  846.                     fields.remove(field_name)

Exception Type: ValueError at /channels/
Exception Value: list.remove(x): x not in list

Before I had to exclude this field specifically, now it's not even there.

[lovelydinosaur]

Before I had to exclude this field specifically, now it's not even there.

Sorry could you give the context for what code is giving you this stacktrace?

What's the most minimal example of a model and serializer that reproduces it?

[maryokhin]

class Channel(models.Model):
    name = models.CharField(max_length=128)

class Subscription(models.Model):
    channel = models.ForeignKey(Channel, related_name='subscribers')

class ChannelSerializer(ModelSerializer):
    class Meta():
        model = Channel
        exclude = ('subscribers', )

Here I would have something like the following:

exclude = ('subscribers',)
field_name = 'subscribers'
fields = ['id', 'name']

I think that I had reverse relationships populated on 2.4.4, which is why I excluded it.

In any case, if it's a field name not in the ones that the serializer has (default or declared) it'll spill an unfriendly stack trace when trying to remove it.

[lovelydinosaur]

Okay, reverse relationships are not (have never been) included by default, so you don't need to do this, but we should clearly be more graceful in this case.

[lovelydinosaur]

Thanks!

[maryokhin]

I just realized that a long time ago Subscription model was a many-to-many through model, that was probably why it was added to the serializer as a forward relation. Then that changed to a regular many-to-many model, was still excluded, 2.4.4 did't care, 3.0 loudly failed.