UpdateAPIView not raising 404 when not exists in Django REST Framework - django

Question

I'm using Django 2.2 and Django REST Framework.
I have an endpoint to update existing record, extending UpdateAPIView
class FakeOrderPaymentView(generics.UpdateAPIView):
serializer_class = OrderPaymentSerializer
permission_classes = (IsAuthenticated,)
def get_object(self):
log.debug(self.request.data)
order_id = self.request.data.get('order_id', None)
if not order_id:
raise Http404
return self.serializer_class.Meta.model.objects.filter(pk=order_id).first()
def perform_update(self, serializer):
return serializer.save()
def update(self, request, *args, **kwargs):
serializer = self.get_serializer(data=request.data)
serializer.is_valid(raise_exception=True)
instance = self.perform_update(serializer)
instance_serializer = OrderListSerializer(instance)
return Response(instance_serializer.data)
and the OrderPaymentSerializer
class OrderPaymentSerializer(serializers.ModelSerializer):
order_id = serializers.IntegerField(write_only=True, required=False)
order_status = serializers.CharField(write_only=True, required=True)
class Meta:
model = Order
fields = [
'order_status',
'order_id'
]
def create(self, validated_data):
log.debug(validated_data)
return super().create(validated_data)
def update(self, instance, validated_data):
status = validated_data.pop('order_status', None)
order_id = validated_data.pop('order_id', None)
instance.status = Order.STATUS.COMPLETED
return super().update(instance, validated_data)
The order_id and order_status are not model fields. They are just to carry data.
If order_id is not in the PUT data or order_id is blank. It should raise 404 response.
But, it's not calling get_object() method before update().
Also, even if I pass order_id in the PUT data. The perform_update() method is calling serializer's create() method instead of update() method.
When is serializer's update() method called?
Why get_object() is not calling automatically?

Answer 1

When is serializer's update() method called?
As the documentation states:
Calling .save() will either create a new instance, or update an existing instance, depending on if an existing instance was passed when instantiating the serializer class
Since you are not providing an instance when instantiating the serializer, calling save will translate into create instead of update.
Why get_object() is not calling automatically?
Because you view's update method is overridden and you didn't call get_object. Default DRF update is:
def update(self, request, *args, **kwargs):
partial = kwargs.pop('partial', False)
instance = self.get_object()
serializer = self.get_serializer(instance, data=request.data, partial=partial)
serializer.is_valid(raise_exception=True)
self.perform_update(serializer)
if getattr(instance, '_prefetched_objects_cache', None):
# If 'prefetch_related' has been applied to a queryset, we need to
# forcibly invalidate the prefetch cache on the instance.
instance._prefetched_objects_cache = {}
return Response(serializer.data)