old_contents: from rest_framework import serializers
  
  from . import models
  
  
  class OpenStackItemSerializer(serializers.HyperlinkedModelSerializer):
      class Meta(object):
          model = models.OpenStackItem
          fields = ('package_details', 'package', 'price', 'start', 'end')
          extra_kwargs = {
              'package': {'lookup_field': 'uuid', 'view_name': 'openstack-package-detail'},
          }
  
      def to_representation(self, instance):
          instance.package_details['name'] = instance.name
          return super(OpenStackItemSerializer, self).to_representation(instance)
  
  
  class InvoiceSerializer(serializers.HyperlinkedModelSerializer):
      total = serializers.DecimalField(max_digits=15, decimal_places=7)
      openstack_items = OpenStackItemSerializer(many=True)
  
      class Meta(object):
          model = models.Invoice
          fields = (
              'url', 'uuid', 'customer', 'total', 'openstack_items', 'state', 'year', 'month'
          )
          view_name = 'invoice-detail'
          extra_kwargs = {
              'url': {'lookup_field': 'uuid'},
              'customer': {'lookup_field': 'uuid'},
          }
  
new_contents: from rest_framework import serializers
  
  from . import models
  
  
  class OpenStackItemSerializer(serializers.HyperlinkedModelSerializer):
      class Meta(object):
          model = models.OpenStackItem
          fields = ('package_details', 'package', 'price', 'start', 'end')
          extra_kwargs = {
              'package': {'lookup_field': 'uuid', 'view_name': 'openstack-package-detail'},
          }
  
      def to_representation(self, instance):
          instance.package_details['name'] = instance.name
          return super(OpenStackItemSerializer, self).to_representation(instance)
  
  
  class InvoiceSerializer(serializers.HyperlinkedModelSerializer):
      total = serializers.DecimalField(max_digits=15, decimal_places=7)
      openstack_items = OpenStackItemSerializer(many=True)
  
      class Meta(object):
          model = models.Invoice
          fields = (
              'url', 'uuid', 'customer', 'total', 'openstack_items', 'state', 'year', 'month'
          )
          extra_kwargs = {
              'url': {'lookup_field': 'uuid'},
              'customer': {'lookup_field': 'uuid'},
          }
  
subject: Remove redundant view_name variable in serializer