Aggregate (and other annotated) fields in Django Rest Framework serializers

Question

I am trying to figure out the best way to add annotated fields, such as any aggregated (calculated) fields to DRF (Model)Serializers. My use case is simply a situation where

Answer 1

Possible solution:

views.py

class IceCreamCompanyViewSet(viewsets.ModelViewSet):
    queryset = IceCreamCompany.objects.all()
    serializer_class = IceCreamCompanySerializer

    def get_queryset(self):
        return IceCreamCompany.objects.annotate(
            total_trucks=Count('trucks'),
            total_capacity=Sum('trucks__capacity')
        )

serializers.py

class IceCreamCompanySerializer(serializers.ModelSerializer):
    total_trucks = serializers.IntegerField()
    total_capacity = serializers.IntegerField()

    class Meta:
        model = IceCreamCompany
        fields = ('name', 'total_trucks', 'total_capacity')

By using Serializer fields I got a small example to work. The fields must be declared as the serializer's class attributes so DRF won't throw an error about them not existing in the IceCreamCompany model.