Tweaks

docs/topics/3.0-announcement.md

@@ -144,6 +144,12 @@ The corresponding code would now look like this:
         logging.info('Creating ticket "%s"' % name)
         serializer.save(user=request.user)  # Include the user when saving.
 
+#### Use `rest_framework.exceptions.ValidationFailed`.
+
+Django's `ValidationError` class is intended for use with HTML forms and it's API makes its use slightly awkward with nested validation errors as can occur in serializers.
+
+We now include a simpler `ValidationFailed` exception class in REST framework that you should use when raising validation failures.
+
 #### 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:

rest_framework/serializers.py

@@ -555,7 +555,7 @@ class ModelSerializer(Serializer):
         depth = getattr(self.Meta, 'depth', 0)
         extra_kwargs = getattr(self.Meta, 'extra_kwargs', {})
 
-        assert not fields and exclude,  "Cannot set both 'fields' and 'exclude'."
+        assert not (fields and exclude),  "Cannot set both 'fields' and 'exclude'."
 
         extra_kwargs = self._include_additional_options(extra_kwargs)