code: def mark_seen(self, medium):
          
          EventSeen.objects.bulk_create([
              EventSeen(event=event, medium=medium) for event in self
          ])
docs: Creates EventSeen objects for the provided medium for every event
          in the queryset.
  
          Creating these EventSeen objects ensures they will not be
          returned when passing ``seen=False`` to any of the medium
          event retrieval functions, ``events``, ``entity_events``, or
          ``events_targets``.