Django : KeyError: "Получена ошибка KeyError при попытке получить значение для поля `channel` на сериализаторе ``...

модель

class Metric(models.Model):

    date = models.DateField()
    channel = models.CharField(max_length=50)
    country = models.CharField(max_length=10)
    os = models.CharField(max_length=10)
    impressions = models.IntegerField()
    clicks = models.IntegerField()    

    def __str__(self):
        return "{} - {}".format(self.date, self.channel)

Мое мнение

class MetricViewSet(viewsets.ModelViewSet):

    serializer_class = MetricSerializer
    queryset = Metric.objects.all()
    filter_backends = [DjangoFilterBackend]
    filterset_class = MetricFilter

Мой сериализатор

class MetricSerializer(serializers.ModelSerializer):
    class Meta:
        model = Metric
        fields = '__all__'

Мне нужно сгруппировать по одному или нескольким столбцам: дата, канал, страна, операционная система и сериализовать это. Может ли кто-нибудь помочь мне, как я могу это сделать?

select channel, country, sum(impressions) as impressions, sum(clicks) as clicks from sample dataset where date < '2017-06-01' group by channel, country order by clicks desc;
     channel      | country | impressions | clicks 
------------------+---------+-------------+--------
 adcolony         | US      |      532608 |  13089
 apple_search_ads | US      |      369993 |  11457
 vungle           | GB      |      266470 |   9430
 vungle           | US      |      266976 |   7937

Мое мнение

lass MetricViewSet(viewsets.ModelViewSet):

    serializer_class = MetricSerializer
    queryset = Metric.objects.all()
    filter_backends = [DjangoFilterBackend]
    filterset_class = MetricFilter

    def get_queryset(self):
        sort_by_dict = {'asc': '', 'desc': '-'}
        queryset = Metric.objects.all()        
        group_by = self.request.query_params.get('group_by', None)
        # grouping the queryset
        if group_by is not None:
            queryset = queryset.values(group_by).annotate(dcount=Count(group_by))#.order_by()               

        return queryset

Я получаю следующую ошибку

KeyError: "Got KeyError when attempting to get a value for field `channel` on serializer `MetricSerializer`.\nThe serializer field might be named incorrectly and not match any attribute or key on the `dict` instance.\nOriginal exception text was: 'channel'."

from django.db.models import Sum


queryset.values('channel', 'country').order_by().annotate(impressions = sum('impressions'),clicks = sum('clicks'))

 if group_by is not None:       
    queryset = queryset.values(group_by).order_by().annotate(impressions = sum('impressions'),clicks = sum('clicks'))

from rest_framework import serializers

class MetricSerializer(serializers.Serializer):

         date = serializers.DateField()
         channel = title = serializers.CharField(required=False, max_length=50, allow_blank=True)
         country = title = serializers.CharField(required=False, max_length=10, allow_blank=True)
         os = title = serializers.CharField(required=False, max_length=10, allow_blank=True)
         impressions = serializers.IntegerField()
         clicks = serializers.IntegerField()