Merge pull request #541 from yprez/default_and_partial_serializers2

Fix "default" values and partial serializers.  Fixes #532.

1 files changed, 3 insertions, 1 deletions

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index a022fe09..c406a2f3 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -186,8 +186,10 @@ class WritableField(Field):
             else:
                 native = data[field_name]
         except KeyError:
-            if self.default is not None:
+            if self.default is not None and not self.root.partial:
                 native = self.default
+                # partial serializers shouldn't set the default field to avoid
+                # overriding the previously set value
             else:
                 if self.required:
                     raise ValidationError(self.error_messages['required'])