Django Rest Framework : How to add a custom field to the response of the GET request?

Question

I'm new to DRF and have just started building an API.

I've a model called Shop. And I've two user different user types : Customer and Supplier.

1. I want to add a custom field distance to the response of the GET request /shops/id/, which represents the distance between the Customer that is submitted the request and the corresponding shop.
2. I think I cannot use SerializerMethodField since the value of the method is not only depend on the object itself.
3. I do not want to add this custom field for all GET requests, instead, I need to add it, when the user that is submitted the request is a Customer.

Considering constraints above, how should I add the custom field to the response of the request? What's the best way to do this ?

Answer 1

You can define a distance SerializerMethodField, and there access the current user location using serializer's context. Then compute distance using current user location and shop's location.

class ShopSerializer(serializers.ModelSerializer):

    distance = serializers.SerializerMethodField()

    class Meta:
        model = Shop
        fields = (.., 'distance')

    def get_distance(self, obj):
        current_user = self.context['request'].user # access current user    
        user_location = current_user.location

        distance = <compute distance using obj.location and user_location>
        return distance