Tweak pre/post save hooks. Return instance in .update().

docs/topics/3.0-announcement.md

@@ -116,11 +116,12 @@ This would now be split out into two separate methods.
         instance.language = validated_data.get('language', instance.language)
         instance.style = validated_data.get('style', instance.style)
         instance.save()
+        return instance
 
 	def create(self, validated_data):
         return Snippet.objects.create(**validated_data)
 
-Note that the `.create` method should return the newly created object instance.
+Note that these methods should return the newly created object instance.
 
 #### Use `.validated_data` instead of `.object`.
 
@@ -592,18 +593,27 @@ The `UniqueTogetherValidator` should be applied to a serializer, and takes a `qu
 
 The view logic for the default method handlers has been significantly simplified, due to the new serializers API.
 
-#### Removal of pre/post save hooks. 
+#### Changes to pre/post save hooks. 
 
-The following method hooks no longer exist on the new, simplified, generic views: `pre_save`, `post_save`, `pre_delete`, `post_delete`.
+The `pre_save` and `post_save` hooks no longer exist, but are replaced with `perform_create(self, serializer)` and `perform_update(self, serializer)`.
 
-If you do need custom behavior, you might choose to instead override the `.save()` method on your serializer class. For example:
+These method should save the object instance by calling `serializer.save()`, adding in any explicit additional arguments as required. They may also perform any custom pre-save or post-save behavior.
 
-    def save(self, *args, **kwargs):
+For example:
-        instance = super(MySerializer).save(*args, **kwarg)
+
+    def perform_create(self, serializer):
+        # Include the owner attribute directly, rather than from request data.
+        instance = serializer.save(owner=self.request.user)
+        # Perform a custom post-save action.
         send_email(instance.to_email, instance.message)
-		return instance
 
-Alternatively write your view logic exlpicitly, or tie your pre/post save behavior into the model class or model manager.
+The `pre_delete` and `post_delete` hooks no longer exist, and are replaced with `.perform_destroy(self, instance)`, which should delete the instance and perform any custom actions.
+
+    def perform_destroy(self, instance):
+        # Perform a custom pre-delete action.
+        send_deletion_alert(user=instance.created_by, deleted=instance)
+        # Delete the object instance.
+        instance.delete()
 
 #### Removal of view attributes.
 

rest_framework/mixins.py

@@ -20,11 +20,11 @@ class CreateModelMixin(object):
     def create(self, request, *args, **kwargs):
         serializer = self.get_serializer(data=request.data)
         serializer.is_valid(raise_exception=True)
-        self.create_valid(serializer)
+        self.perform_create(serializer)
         headers = self.get_success_headers(serializer.data)
         return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
 
-    def create_valid(self, serializer):
+    def perform_create(self, serializer):
         serializer.save()
 
     def get_success_headers(self, data):
@@ -67,10 +67,10 @@ class UpdateModelMixin(object):
         instance = self.get_object()
         serializer = self.get_serializer(instance, data=request.data, partial=partial)
         serializer.is_valid(raise_exception=True)
-        self.update_valid(serializer)
+        self.preform_update(serializer)
         return Response(serializer.data)
 
-    def update_valid(self, serializer):
+    def preform_update(self, serializer):
         serializer.save()
 
     def partial_update(self, request, *args, **kwargs):
@@ -84,9 +84,12 @@ class DestroyModelMixin(object):
     """
     def destroy(self, request, *args, **kwargs):
         instance = self.get_object()
-        instance.delete()
+        self.perform_destroy(instance)
         return Response(status=status.HTTP_204_NO_CONTENT)
 
+    def perform_destroy(self, instance):
+        instance.delete()
+
 
 # The AllowPUTAsCreateMixin was previously the default behaviour
 # for PUT requests. This has now been removed and must be *explicitly*

rest_framework/serializers.py

@@ -83,7 +83,10 @@ class BaseSerializer(Field):
             )
 
         if self.instance is not None:
-            self.update(self.instance, validated_data)
+            self.instance = self.update(self.instance, validated_data)
+            assert self.instance is not None, (
+                '`update()` did not return an object instance.'
+            )
         else:
             self.instance = self.create(validated_data)
             assert self.instance is not None, (
@@ -444,19 +447,19 @@ class ModelSerializer(Serializer):
                 self.validators.extend(validators)
                 self._kwargs['validators'] = validators
 
-    def create(self, attrs):
+    def create(self, validated_attrs):
         ModelClass = self.Meta.model
 
-        # Remove many-to-many relationships from attrs.
+        # Remove many-to-many relationships from validated_attrs.
         # They are not valid arguments to the default `.create()` method,
         # as they require that the instance has already been saved.
         info = model_meta.get_field_info(ModelClass)
         many_to_many = {}
         for field_name, relation_info in info.relations.items():
-            if relation_info.to_many and (field_name in attrs):
+            if relation_info.to_many and (field_name in validated_attrs):
-                many_to_many[field_name] = attrs.pop(field_name)
+                many_to_many[field_name] = validated_attrs.pop(field_name)
 
-        instance = ModelClass.objects.create(**attrs)
+        instance = ModelClass.objects.create(**validated_attrs)
 
         # Save many-to-many relationships after the instance is created.
         if many_to_many:
@@ -465,10 +468,11 @@ class ModelSerializer(Serializer):
 
         return instance
 
-    def update(self, obj, attrs):
+    def update(self, instance, validated_attrs):
-        for attr, value in attrs.items():
+        for attr, value in validated_attrs.items():
-            setattr(obj, attr, value)
+            setattr(instance, attr, value)
-        obj.save()
+        instance.save()
+        return instance
 
     def get_unique_together_validators(self):
         field_names = set([