Multiple fields with the same source clobber each other #4634
Description
Hey guys, I'm getting weird behavior with many related fields. Is this an error?
Checklist
- I have verified that that issue exists against the
masterbranch of Django REST framework. - I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
- This is not a usage question. (Those should be directed to the discussion group instead.)
- This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
- I have reduced the issue to the simplest possible case.
- I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)
Steps to reproduce
Create a model serializer where one field renders the relation, and the other field writes to it.
class UserSerializer(serializers.ModelSerializer):
dogs = DogSerializer(many=True, read_only=True)
dog_ids = serializers.PrimaryKeyRelatedField(source='dogs', many=True, queryset=Dog.objects.all())
class Meta:
fields = ('dogs', 'dog_ids',)
model = UserThen do a patch.
PATCH /api/users/23 HTTP/1.1
Content-Type: application/json
{
"dog_ids": [5, 9]
}
Expected behavior
It should update my model.
Actual behavior
It throws an error complaining that nested writes aren't allowed.
AssertionError at /api/users/23
The `.update()` method does not support writable nestedfields by default.
Write an explicit `.update()` method for serializer `app.serializers.DogSerializer`, or set `read_only=True` on nested serializer fields.
tl;dr
This assertion gets called, but it checks all fields rather than just the writable ones:
https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/serializers.py#L721
def raise_errors_on_nested_writes(method_name, serializer, validated_data):
assert not any(
isinstance(field, BaseSerializer) and
(key in validated_data) and
isinstance(validated_data[key], (list, dict))
for key, field in serializer.fields.items()
), (
'The `.{method_name}()` method does not support writable nested'
'fields by default.\nWrite an explicit `.{method_name}()` method for '
'serializer `{module}.{class_name}`, or set `read_only=True` on '
'nested serializer fields.'.format(
method_name=method_name,
module=serializer.__class__.__module__,
class_name=serializer.__class__.__name__
)
)