old_contents: from rest_framework.generics import ListAPIView
  
  from leaderboard.locations.models import Country
  from leaderboard.locations.serializers import CountrySerializer
  
  
  class ListCountriesView(ListAPIView):
      serializer_class = CountrySerializer
      queryset = Country.objects.all().annotate_observations()
      pagination_class = None
  
new_contents: from rest_framework.generics import ListAPIView
  
  from leaderboard.locations.models import Country
  from leaderboard.locations.serializers import CountrySerializer
  
  
  class ListCountriesView(ListAPIView):
      serializer_class = CountrySerializer
      queryset = (Country.objects
                         .all()
                         .annotate_observations()
                         .only('name', 'iso2'))
      pagination_class = None
  
subject: Improve performance of /countries/ API call #136