Tweaks

docs/topics/3.0-announcement.md

@@ -144,6 +144,24 @@ The corresponding code would now look like this:
         logging.info('Creating ticket "%s"' % name)
         serializer.save(user=request.user)  # Include the user when saving.
 
+#### Change to `validate_<field_name>`.
+
+The `validate_<field_name>` method hooks that can be attached to serializer classes change their signature slightly and return type. Previously these would take a dictionary of all incoming data, and a key representing the field name, and would return a dictionary including the validated data for that field:
+
+    def validate_score(self, attrs, source):
+        if attrs[score] % 10 != 0:
+            raise ValidationError('This field should be a multiple of ten.')
+        return attrs
+
+This is now simplified slightly, and the method hooks simply take the value to be validated, and return it's validated value.
+
+    def validate_score(self, value):
+        if value % 10 != 0:
+            raise ValidationError('This field should be a multiple of ten.')
+        return value
+
+Any ad-hoc validation that applies to more than one field should go in the `.validate(self, attrs)` method as usual.
+
 #### Limitations of ModelSerializer validation.
 
 This change also means that we no longer use the `.full_clean()` method on model instances, but instead perform all validation explicitly on the serializer. This gives a cleaner separation, and ensures that there's no automatic validation behavior on `ModelSerializer` classes that can't also be easily replicated on regular `Serializer` classes.

rest_framework/relations.py

@@ -264,9 +264,10 @@ class ManyRelation(Field):
         ]
 
     def to_representation(self, obj):
+        iterable = obj.all() if (hasattr(obj, 'all')) else obj
         return [
             self.child_relation.to_representation(value)
-            for value in obj.all()
+            for value in iterable
         ]
 
     @property