Raise error for dotted sources on creation.

rest_framework/fields.py

@@ -251,6 +251,7 @@ class WritableField(Field):
     default_error_messages = {
         'required': _('This field is required.'),
         'invalid': _('Invalid value.'),
+        'missing': _('Related object does not exist.'),
     }
     widget = widgets.TextInput
     default = None

rest_framework/serializers.py

@@ -20,6 +20,7 @@ from django.core.paginator import Page
 from django.db import models
 from django.forms import widgets
 from django.utils.datastructures import SortedDict
+from django.utils.translation import ugettext_lazy as _
 from rest_framework.compat import get_concrete_model, six
 from rest_framework.settings import api_settings
 
@@ -919,6 +920,7 @@ class ModelSerializer(Serializer):
         """
         m2m_data = {}
         related_data = {}
+        related_models_to_save = {}
         nested_forward_relations = {}
         meta = self.opts.model._meta
 
@@ -948,11 +950,22 @@ class ModelSerializer(Serializer):
         # Update an existing instance...
         if instance is not None:
             for key, val in attrs.items():
-                # TODO: check whether we need to do something about dotted paths
+                # Follow relations if needed
                 dest = instance
                 keys = key.split('.')
-                for related_instance in keys[:-1]:
-                    dest = getattr(dest, related_instance)
+                try:
+                    for related_instance in keys[:-1]:
+                        dest = getattr(dest, related_instance)
+
+                except AttributeError:
+                    self._errors[key] = self.error_messages['missing']
+                    continue
+
+                # If there's a relation, mark the object to save
+                if len(keys) > 1:
+                    related_models_to_save[key] = dest
+
+                # Assign the value
                 try:
                     setattr(dest, keys[-1], val)
                 except ValueError:
@@ -960,8 +973,11 @@ class ModelSerializer(Serializer):
 
         # ...or create a new instance
         else:
+            for key, value in ((k, v) for k, v in attrs.items() if '.' in k):
+                self._errors[key] = 'You can not set dotted sources during creation.'
+                del attrs[key]
+                print value
             instance = self.opts.model(**attrs)
-            # TODO: check whether we need to do something about dotted paths
 
         # Any relations that cannot be set until we've
         # saved the model get hidden away on these
@@ -970,6 +986,7 @@ class ModelSerializer(Serializer):
         instance._related_data = related_data
         instance._m2m_data = m2m_data
         instance._nested_forward_relations = nested_forward_relations
+        instance._related_models_to_save = related_models_to_save
 
         return instance
 
@@ -1028,6 +1045,10 @@ class ModelSerializer(Serializer):
                     setattr(obj, accessor_name, related)
             del(obj._related_data)
 
+        if getattr(obj, '_related_models_to_save', None):
+            for related in obj._related_models_to_save.values():
+                self.save_object(related)
+
 
 class HyperlinkedModelSerializerOptions(ModelSerializerOptions):
     """

rest_framework/tests/test_serializer.py

@@ -1843,7 +1843,8 @@ class BoolenFieldTypeTest(TestCase):
 
 
 class RelationSpanningSerializerTest(TestCase):
-    def test_regular_field_can_span_a_relation(self):
+    def test_model_traversal_creation(self):
+        """Update a field through a foreign key during a creation."""
         class TicketSerializer(serializers.ModelSerializer):
             name = fields.CharField(source='assigned.name')
 
@@ -1851,9 +1852,40 @@ class RelationSpanningSerializerTest(TestCase):
                 model = Ticket
                 fields = ('name',)
 
+        serializer = TicketSerializer(data={'name': 'doe'})
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(serializer.errors, {'name': 'You can not set dotted sources during creation.'})
+
+    def test_model_traversal_update(self):
+        """Update a field through a foreign key during an update."""
+        class TicketSerializer(serializers.ModelSerializer):
+            name = fields.CharField(source='assigned.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('name',)
+
+        owner = Person.objects.create(name='john')
+        reviewer = Person.objects.create(name='reviewer')
+        ticket = Ticket.objects.create(assigned=owner, reviewer=reviewer)
+        serializer = TicketSerializer(ticket, data={'name': 'doe'})
+        self.assertTrue(serializer.is_valid())
+        self.assertEqual(serializer.object.assigned.name, 'doe')
+        serializer.save()
+        self.assertEqual(Person.objects.get(id=owner.id).name, 'doe')
+
+    def test_failing_model_traversal(self):
+        """Update a field through an unknown relation."""
+        class TicketSerializer(serializers.ModelSerializer):
+            name = fields.CharField(source='demo.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('name',)
+
         owner = Person(name='john')
         reviewer = Person(name='reviewer')
         ticket = Ticket(assigned=owner, reviewer=reviewer)
         serializer = TicketSerializer(ticket, data={'name': 'doe'})
-        self.assertTrue(serializer.is_valid())
-        self.assertEqual(serializer.object.assigned.name, 'doe')
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(serializer.errors, {'name': 'Related object does not exist.'})