Fix the pre_save removal.

docs/tutorial/6-viewsets-and-routers.md

@@ -44,8 +44,8 @@ Next we're going to replace the `SnippetList`, `SnippetDetail` and `SnippetHighl
             snippet = self.get_object()
             return Response(snippet.highlighted)
 
-        def pre_save(self, obj):
-            obj.owner = self.request.user
+        def perform_create(self, serializer):
+            serializer.save(owner=self.request.user)
 
 This time we've used the `ModelViewSet` class in order to get the complete set of default read and write operations.
 
@@ -53,6 +53,20 @@ Notice that we've also used the `@detail_route` decorator to create a custom act
 
 Custom actions which use the `@detail_route` decorator will respond to `GET` requests.  We can use the `methods` argument if we wanted an action that responded to `POST` requests.
 
+Also note that we are setting the `owner` as the `request.user`. However, to make this work, we need to customize the associated serializer:
+
+    class SnippetSerializer(serializers.HyperlinkedModelSerializer):
+        owner = serializers.ReadOnlyField(source='owner.username')
+        highlight = serializers.HyperlinkedIdentityField(view_name='snippet-highlight', format='html')
+
+        class Meta:
+            model = Snippet
+            fields = ('url', 'highlight', 'owner',
+                      'title', 'code', 'linenos', 'language', 'style')
+
+        def create(self, validated_data):
+            return Snippet.objects.create(**validated_data)
+
 ## Binding ViewSets to URLs explicitly
 
 The handler methods only get bound to the actions when we define the URLConf.