Dynamically adding field in Django Rest Framework generics.ListAPIView

Question

I have a view that can be called with a longitude and latitude parameters.

When those parameters are set, I want the response to add the distance fields in the serialization.

Here is how I do that:

def get_queryset(self):
    latitude = self.request.QUERY_PARAMS.get('latitude', None)
    longitude = self.request.QUERY_PARAMS.get('longitude', None)
    if latitude and longitude:
        center = fromstr('POINT(%s %s)'%(latitude,longitude))
        queryset = queryset.distance(center).order_by('distance')
        self.serializer_class.distance = serializers.CharField(source='distance')
        self.serializer_class.Meta.fields += ('distance',)
    return queryset.all()

I think I could have done if differently, with two separate serializer_class.

I am wondering if it would have been better, what do you think?

Answer 1

I guess distance is None where longitude and latitude aren't given?

I'd be inclined to define the distance field on the serializer itself, rather than adding it dynamically on the view.

For the case where distance is None — if I didn't want it in the response — I would override to_native on the serializer to remove it. E.g:

def to_native(self, obj):
    ret = super(MySerializer, self).to_native(obj)
    if ret['distance'] is None:         
        del ret['distance']
    return ret

The end result is the same but this approach is more cohesive. I hope that helps.