old_contents: from rest_framework.serializers import ModelSerializer
  from .models import CountInstance
  
  
  class CountInstanceSerializer(ModelSerializer):
      class Meta:
          model = CountInstance
  
new_contents: from rest_framework.serializers import ModelSerializer
  from .models import CountInstance
  
  
  class CountInstanceSerializer(ModelSerializer):
      class Meta:
          model = CountInstance
          fields = ('count_total',)
  
subject: Update serializer to deal with new model