title: ModelViewSet - Update nested field
body: <p>I'm currently working on Django with Django Rest Framwork.</p>
  
  <p>I can't update my object within nested object field.</p>
  
  <hr>
  
  <p><strong>serializer.py</strong></p>
  
  <pre><code>class OwnerSerializer(serializers.ModelSerializer):
      class Meta:
          model =  Owner
          fields = ('id', 'name')
  
  class CarSerializer(serializers.ModelSerializer):
      owner = ownerSerializer(many=False, read_only=False) 
      class Meta:
          model =  Car
          fields = ('id', 'name', 'owner')
  </code></pre>
  
  <p><strong>view.py</strong></p>
  
  <pre><code>class OwnerViewSet(viewsets.ModelViewSet):
      queryset = Owner.objects.all()
      serializer_class = OwnerSerializer
  
  class CarViewSet(viewsets.ModelViewSet):
      serializer_class = CarSerializer
      queryset = Car.objects.all()
  
      def create(self, request):
          serialized = self.serializer_class(data=request.DATA)
          if serialized.is_valid():
              serialized.save()
              return Response(status=HTTP_202_ACCEPTED)
          else:
              return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
  </code></pre>
  
  <hr>
  
  <p>When I do this :</p>
  
  <pre><code>Request URL:http://localhost:9000/api/v1/cars/1/?format=json
  Request Method:PUT
  Request Paylod :
  {
      "id":1,
      "name": "TEST", 
      "ower": {
          "id":1,
          "name": "owner_test"
      }
  }
  </code></pre>
  
  <p>I get the following Response :</p>
  
  <pre><code>The `.update()` method does not support writable nestedfields by default.
  Write an explicit `.update()` method for serializer `app.serializers.CarSerializer`,
  or set `read_only=True` on nested serializer fields.
  </code></pre>
  
  <hr>
  
  <p>Knowing :</p>
  
  <ul>
  <li>I want to keep the owner serialization on GET;</li>
  <li>We can imagine the car nested by another object and ect...</li>
  </ul>
  
  <p>How can I do if i want to change the owner when I update the car.</p>