code: def create_connection(self, from_obj, to_obj):
          
          self._validate_ctypes(from_obj, to_obj)
          return Connection.objects.get_or_create(relationship_name=self.name,
                                                  from_pk=from_obj.pk, to_pk=to_obj.pk)[0]
docs: Creates and returns a connection between the given objects. If a
          connection already exists, that connection will be returned instead.