title: When are create and update called in djangorestframework serializer?
body: <p>I'm currently implementing djangorestframework for my app RESTful API. After playing around with it, I still do not clearly understand what <code>.create(self, validated_data)</code> and <code>.update(self, validated_data)</code> used for in the serializer. As I understand, <strong>CRUD</strong> only calls the 4 main methods in <code>viewsets.ModelViewSet</code>: <code>create()</code>, <code>retrive()</code>, <code>update()</code>, and <code>destroy()</code>.</p>
  <p>I also have already tried to debug and print out stuff to see when the <code>.create()</code> and <code>.update()</code> methods are called in both <code>ModelViewSet</code> and <code>ModelSerializer</code>. Apparently, only the methods in <code>ModelViewSet</code> are called when I do the HTTP verbs. However, for <code>ModelSerializer</code>, I don't see any calls in those 2 methods. I just want to know what are those methods used for in <code>ModelSerializer</code> since I see that people override those methods a lot in the serializer.</p>