more bug fixes

mails/settings.py

 """Mails app settings."""
 from django.conf import settings
+import warnings
 
 NOTIFICATIONS_ADDRESS = getattr(settings, 'MAILS_NOTIFICATIONS_ADDRESS')
 ENABLED = getattr(settings, 'MAILS_ENABLED')
 RAISE_EXCEPTIONS = getattr(settings, 'MAILS_RAISE_EXCEPTIONS')
+
+if getattr(settings, 'SENDGRID_API_KEY', None) is None:
+    warnings.warn('SENDGRID_API_KEY is not set, sending emails will fail')

visits/serializers.py

@@ -54,10 +54,7 @@ class VisitListSerializer(serializers.HyperlinkedModelSerializer):
     """Serializer for lists of visits."""
 
     place = serializers.StringRelatedField()
-    participants = serializers.SerializerMethodField()
-
-    def get_participants(self, obj):
-        return obj.participants.values_list('id', flat=True)
+    participants = ParticipationSerializer(source='participations', many=True)
 
     organizers = serializers.SerializerMethodField()
 
@@ -87,7 +84,6 @@ class VisitListSerializer(serializers.HyperlinkedModelSerializer):
 class VisitSerializer(VisitListSerializer):
     """Serializer for Visit."""
 
-    participants = ParticipationSerializer(source='participations', many=True)
     place = PlaceSerializer()
     organizers = VisitOrganizerSerializer(many=True)