[Answered ]-Django ModelViewSet. How to merge two perform methods/functions?

Assign the perform_create function as perform_update as well:

class ArticleView(viewsets.ModelViewSet):
    queryset = Article.objects.all()
    serializer_class = ArticleSerializer

    def perform_create(self, serializer):
        author = get_object_or_404(Author, id=self.request.data['author']['id'])
        return serializer.save(author=author)

    perform_update = perform_create