old_contents: from core.models import ProviderMachine
  from rest_framework import serializers
  
  
  class ProviderMachineSummarySerializer(serializers.HyperlinkedModelSerializer):
  
      class Meta:
          model = ProviderMachine
          view_name = 'api_v2:providermachine-detail'
          fields = ('id', 'url', 'start_date', 'end_date')
  
new_contents: from core.models import ProviderMachine
  from rest_framework import serializers
  from ..summaries import ProviderSummarySerializer
  
  
  class ProviderMachineSummarySerializer(serializers.HyperlinkedModelSerializer):
      provider = ProviderSummarySerializer(source='instance_source.provider')
      start_date = serializers.DateTimeField(source='instance_source.start_date')
      end_date = serializers.DateTimeField(source='instance_source.end_date')
  
      class Meta:
          model = ProviderMachine
          view_name = 'api_v2:providermachine-detail'
          fields = ('id', 'url', 'provider', 'start_date', 'end_date')
  
subject: fix provider_machine summary serializer