How do i serialize objects during enrichment with stream-django and django rest framework? - django-rest-framework

Question

Im using stream-django with django REST framework and the enriched activities are throwing "not JSON serializable" on the objects returned from enrichment, which is as expected as they have not gone through any serializing.
How do i customize the enrichment process so that it returns a serialized object from my drf serializer and not the object itself?
Some example data, not enriched:
"is_seen": false,
"is_read": false,
"group": "19931_2016-04-04",
"created_at": "2016-04-04T08:53:42.601",
"updated_at": "2016-04-04T11:33:26.140",
"id": "0bc8c85a-fa59-11e5-8080-800005683205",
"verb": "message",
"activities": [
{
"origin": null,
"verb": "message",
"time": "2016-04-04T11:33:26.140",
"id": "0bc8c85a-fa59-11e5-8080-800005683205",
"foreign_id": "chat.Message:6",
"target": null,
"to": [
"notification:1"
],
"actor": "auth.User:1",
"object": "chat.Message:6"
}
The view:
def get(self, request, format=None):
user = request.user
enricher = Enrich()
feed = feed_manager.get_notification_feed(user.id)
notifications = feed.get(limit=5)['results']
enriched_activities=enricher.enrich_aggregated_activities(notifications)
return Response(enriched_activities)

Answer 1

I solved it by doing the following:
property tag on the model that returns the serializer class
#property
def activity_object_serializer_class(self):
from .serializers import FooSerializer
return FooSerializer
Then used this to serialize the enriched activities. Supports nesting.
#staticmethod
def get_serialized_object_or_str(obj):
if hasattr(obj, 'activity_object_serializer_class'):
obj = obj.activity_object_serializer_class(obj).data
else:
obj = str(obj) # Could also raise exception here
return obj
def serialize_activities(self, activities):
for activity in activities:
for a in activity['activities']:
a['object'] = self.get_serialized_object_or_str(a['object'])
# The actor is always a auth.User in our case
a['actor'] = UserSerializer(a['actor']).data
return activities
and the view:
def get(self, request, format=None):
user = request.user
enricher = Enrich()
feed = feed_manager.get_notification_feed(user.id)
notifications = feed.get(limit=5)['results']
enriched_activities = enricher.enrich_aggregated_activities(notifications)
serialized_activities = self.serialize_activities(enriched_activities)
return Response(serialized_activities)

Answer 2

The enrich step replaces string references into full Django model instances.
For example: the string "chat.Message:6" is replaced with an instance of chat.models.Message (same as Message.objects.get(pk=6)).
By default DRF does not know how to serialize Django models and fails with a serialization error. Luckily serializing models is a very simple task when using DRF. There is a built-in serializer class that is specific to Django models (serializers.ModelSerializer).
The documentation of DRF explains this process in detail here: http://www.django-rest-framework.org/api-guide/serializers/#modelserializer.
In your case you probably need to use nested serialization and make the serialization of the object field smart (that field can contain references to different kind of objects).
There is an open issue about this on Github: https://github.com/GetStream/stream-django/issues/38. Ideally this is something the library will provide as helper/example, so any code contribution / input will help making that happen.