          model = self.resource.model
  
          # TODO: update on the url of a non-existing resource url doesn't work correctly at the moment - will end up with a new url
          try:
              self.model_instance = model.objects.get(self.build_query(*args, **kwargs))
  
              for (key, val) in self.CONTENT.items():
                  setattr(self.model_instance, key, val)
          except model.DoesNotExist:
              self.model_instance = model(**self.get_instance_data(model, self.CONTENT, *args, **kwargs))
 
</s> remove             self.model_instance = model.objects.get(self.build_query(*args, **kwargs))
 </s> add             self.model_instance = self.get_object(*args, **kwargs) </s> remove             instance = model.objects.get(self.build_query(*args, **kwargs))
 </s> add             instance = self.get_object(*args, **kwargs) </s> remove from djangorestframework.response import Response
 </s> add from djangorestframework.response import Response, ErrorResponse </s> remove from djangorestframework.mixins import CreateModelMixin, PaginatorMixin
 </s> add from djangorestframework.mixins import CreateModelMixin, PaginatorMixin, ReadModelMixin
            self.model_instance = self.get_object(*args, **kwargs)
          model = self.resource.model
  
          # TODO: update on the url of a non-existing resource url doesn't work correctly at the moment - will end up with a new url
          try:
            self.model_instance = self.get_object(*args, **kwargs)
  
              for (key, val) in self.CONTENT.items():
                  setattr(self.model_instance, key, val)
          except model.DoesNotExist:
              self.model_instance = model(**self.get_instance_data(model, self.CONTENT, *args, **kwargs))
keep keep keep keep replace keep keep keep keep keep
 Add a get_object method to the ModelMixin, and tests 
djangorestframework/mixins.py