allow DateTimeFields to accept strings as input

[bacongobbler]

I found an interesting "bug" with Django Rest Framework along with how Django's DateTimeField works. Given the following TestCase:

class ReadOnlyDateTimeModel(models.Model):
    date = models.DateTimeField()

    def save(self, *args, **kwargs):
        self.date = '2015-02-03 00:00:00'
        return super(ReadOnlyDateTimeModel, self).save(*args, **kwargs)


class ReadOnlyDateTimeSerializer(serializers.ModelSerializer):
    date = serializers.DateTimeField(read_only=True)

    class Meta:
        model = ReadOnlyDateTimeModel


class ReadOnlyDateTimeView(generics.ListCreateAPIView):
    queryset = ReadOnlyDateTimeModel.objects.all()
    serializer_class = ReadOnlyDateTimeSerializer


class TestReadOnlyFieldSerializer(TestCase):
    def setUp(self):
        self.view = ReadOnlyDateTimeView.as_view()

    def test_model_save_works(self):
        obj = ReadOnlyDateTimeModel.objects.create()
        assert obj.date == '2015-02-03 00:00:00'

    def test_post_root_view(self):
        """
        POST requests to ListCreateAPIView should create a new object.
        """
        data = {'price': 1}
        request = factory.post('/', data, format='json')
        response = self.view(request).render()
        self.assertEqual(response.status_code, status.HTTP_201_CREATED)

I see this error:

tests/test_generics.py:544: in test_post_root_view
    response = self.view(request).render()
/usr/local/lib/python2.7/site-packages/django/views/decorators/csrf.py:57: in wrapped_view
    return view_func(*args, **kwargs)
/usr/local/lib/python2.7/site-packages/django/views/generic/base.py:69: in view
    return self.dispatch(request, *args, **kwargs)
rest_framework/views.py:452: in dispatch
    response = self.handle_exception(exc)
rest_framework/views.py:449: in dispatch
    response = handler(request, *args, **kwargs)
rest_framework/generics.py:244: in post
    return self.create(request, *args, **kwargs)
rest_framework/mixins.py:21: in create
    headers = self.get_success_headers(serializer.data)
rest_framework/serializers.py:466: in data
    ret = super(Serializer, self).data
rest_framework/serializers.py:213: in data
    self._data = self.to_representation(self.instance)
rest_framework/serializers.py:435: in to_representation
    ret[field.field_name] = field.to_representation(attribute)
rest_framework/fields.py:879: in to_representation
    value = value.isoformat()
E   AttributeError: 'unicode' object has no attribute 'isoformat'

It seems like Django will accept a formatted string as input, however DRF tries to format the field as a datetime rather than a string, causing the above failure case. If I change self.date = '2015-02-03 00:00:00' to self.date = datetime.datetime.now(), it all works as expected.

[tomchristie]

Yup, we probably should correctly coerce string values too.
Really the internal value ought to be a datetime instance rather than a raw string, but we should still adopt the more graceful stance.

[luccascorrea]

The error was not fixed for the DateTimeField, only the DateField. I think this issue should be reopened.

[tomchristie]

@luccascorrea Okay, happy to accept a new issue for DateTimeField here (probably best to keep them separate)