From 0ab70ba1705ff0a80f0925167bb2f8c0c3155418 Mon Sep 17 00:00:00 2001
From: Craig de Stigter <craig.destigter@koordinates.com>
Date: Wed, 21 Aug 2013 16:44:20 +1200
Subject: [PATCH 1/2] Handle dotted field.source in writable serializers.

---
 rest_framework/fields.py      | 59 ++++++++++++++++++++++++++++++-----
 rest_framework/relations.py   |  8 +----
 rest_framework/serializers.py |  3 +-
 3 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 07779c472..a0a59523c 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -60,6 +60,18 @@ def get_component(obj, attr_name):
     return val
 
 
+def set_component(obj, attr_name, value):
+    """
+    Given an object, and an attribute name, set that attribute on the object.
+    Mirrors get_component, except set_component doesn't handle callable
+    components.
+    """
+    if isinstance(obj, dict):
+        obj[attr_name] = value
+    else:
+        setattr(obj, attr_name, value)
+
+
 def readable_datetime_formats(formats):
     format = ', '.join(formats).replace(ISO_8601,
              'YYYY-MM-DDThh:mm[:ss[.uuuuuu]][+HHMM|-HHMM|Z]')
@@ -138,6 +150,24 @@ class Field(object):
         if help_text is not None:
             self.help_text = strip_multiple_choice_msg(smart_text(help_text))
 
+    def _get_source_value(self, obj, field_name):
+        """
+        Given an object and a field name, traverses the components in
+        self.source/field_name and returns the source value from the object.
+
+        The source/field_name may contain dot-separated components.
+        Each component should refer to an attribute, a dict key, or a
+        callable with no arguments.
+        """
+        source = self.source or field_name
+        value = obj
+
+        for component in source.split('.'):
+            value = get_component(value, component)
+            if value is None:
+                break
+        return value
+
     def initialize(self, parent, field_name):
         """
         Called to set up a field prior to field_to_native or field_from_native.
@@ -170,13 +200,7 @@ class Field(object):
         if self.source == '*':
             return self.to_native(obj)
 
-        source = self.source or field_name
-        value = obj
-
-        for component in source.split('.'):
-            value = get_component(value, component)
-            if value is None:
-                break
+        value = self._get_source_value(obj, field_name)
 
         return self.to_native(value)
 
@@ -297,6 +321,27 @@ class WritableField(Field):
         if errors:
             raise ValidationError(errors)
 
+    def _set_source_value(self, obj, field_name, value):
+        """
+        Looks up a field on the given object and sets its value.
+        Uses self.source if set, otherwise the given field name.
+
+        This obeys the same rules as _get_source_value, except that the
+        final component of self.source/field_name can't be a callable.
+        """
+        source = self.source or field_name
+        parts = source.split('.')
+        last_source_part = parts.pop()
+
+        item = obj
+        for component in parts:
+            item = get_component(item, component)
+            if item is None:
+                raise ValueError(
+                    "can't set %r: component %r is None" % (source, component)
+                )
+        set_component(item, last_source_part, value)
+
     def field_from_native(self, data, files, field_name, into):
         """
         Given a dictionary and a field name, updates the dictionary `into`,
diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index edaf76d6e..d5d90e49a 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -130,13 +130,7 @@ class RelatedField(WritableField):
             if self.source == '*':
                 return self.to_native(obj)
 
-            source = self.source or field_name
-            value = obj
-
-            for component in source.split('.'):
-                value = get_component(value, component)
-                if value is None:
-                    break
+            value = self._get_source_value(obj, field_name)
         except ObjectDoesNotExist:
             return None
 
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 31cfa3447..c37a049e1 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -289,7 +289,8 @@ class BaseSerializer(WritableField):
         are instantiated.
         """
         if instance is not None:
-            instance.update(attrs)
+            for k, v in attrs.items():
+                self._set_source_value(instance, k, v)
             return instance
         return attrs
 

From d5d97624f702d0ae1aa68a8ecb5aa215f84c6316 Mon Sep 17 00:00:00 2001
From: Craig de Stigter <craig.destigter@koordinates.com>
Date: Wed, 21 Aug 2013 16:54:49 +1200
Subject: [PATCH 2/2] more explicit/obvious error if you try to do writable
 dotted field.source with a callable final component

---
 rest_framework/fields.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index a0a59523c..21daa91b4 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -69,6 +69,9 @@ def set_component(obj, attr_name, value):
     if isinstance(obj, dict):
         obj[attr_name] = value
     else:
+        attr = getattr(obj, attr_name)
+        if six.callable(attr):
+            raise TypeError("%r.%s is a method; can't set it" % (obj, attr_name))
         setattr(obj, attr_name, value)
 
 
@@ -336,10 +339,6 @@ class WritableField(Field):
         item = obj
         for component in parts:
             item = get_component(item, component)
-            if item is None:
-                raise ValueError(
-                    "can't set %r: component %r is None" % (source, component)
-                )
         set_component(item, last_source_part, value)
 
     def field_from_native(self, data, files, field_name, into):