old_contents: from core.models import Volume
  from rest_framework import serializers
  
  
  class VolumeSummarySerializer(serializers.HyperlinkedModelSerializer):
      provider = serializers.PrimaryKeyRelatedField(source='instance_source.provider', read_only=True)
      start_date = serializers.DateTimeField(source='instance_source.start_date')
      end_date = serializers.DateTimeField(source='instance_source.end_date')
  
      class Meta:
          model = Volume
          view_name = 'api_v2:volume-detail'
          fields = ('id', 'url', 'name', 'size', 'provider', 'start_date', 'end_date')
new_contents: from core.models import Volume
  from rest_framework import serializers
  from ..summaries import IdentitySummarySerializer
  
  
  class VolumeSummarySerializer(serializers.HyperlinkedModelSerializer):
      identity = IdentitySummarySerializer(source='instance_source.created_by_identity')
      provider = serializers.PrimaryKeyRelatedField(source='instance_source.provider', read_only=True)
      start_date = serializers.DateTimeField(source='instance_source.start_date')
      end_date = serializers.DateTimeField(source='instance_source.end_date')
  
      class Meta:
          model = Volume
          view_name = 'api_v2:volume-detail'
          fields = ('id', 'url', 'name', 'size', 'identity', 'provider', 'start_date', 'end_date')
subject: add identity to volume summary serializer