Pass parameter to Django REST framework serializer to use with model - django

Question

I have a class Object with a method state that takes a datetime parameter dt. How do I pass the datetime parameter from the URL to Object.state()?
The model:
class Object(models.Model):
def state(self, dt=datetime.datetime.now()) -> dict:
...stuff...
return {'dt': dt, 'other_stuff': stuff}
The view:
class ObjectDetail(generics.RetrieveAPIView):
queryset = models.Object.objects.all()
serializer_class = serializers.ObjectSerializer
def get_serializer_context(self):
return {'dt': self.request.query_params.get('dt', datetime.datetime.now())}
def get(self, request, *args, **kwargs):
return self.retrieve(request, *args, **kwargs)
And the serializer classes:
class ObjectSerializer(serializers.HyperlinkedModelSerializer):
state = StateSerializer(read_only=True, context={'dt': self.context['dt']})
class Meta:
model = models.Object
fields = ('state')
class StateSerializer(serializers.Serializer):
dt = serializers.DateTimeField()
... other stuff...
As you can see I am trying to pass dt as extra context in the line state = StateSerializer(read_only=True, context={'dt': dt}) having set the context earlier in the view. The problem here is that when ObjectSerializer is initialized dt is not accessible via self.context['dt'] as self is not defined.

Answer 1

The solution is to make state a serializers.SerializerMethodField() and then define a get_state method. The new ObjectSeializer looks like this:
class ObjectSerializer(serializers.HyperlinkedModelSerializer):
state = serializers.SerializerMethodField()
class Meta:
model = models.Object
fields = ('state')
def get_state(self, obj):
state = obj.state(self.context['dt'])
state_serializer = StateSerializer(state)
return state_serializer.data