From c9b9ec93f924a0cb2eee7c4fd9afad8f8491dfe7 Mon Sep 17 00:00:00 2001
From: Konsta Vesterinen <konsta.vesterinen@gmail.com>
Date: Mon, 20 Jan 2014 21:30:54 +0200
Subject: [PATCH] Fix nullify generic relationship

---
 sqlalchemy_utils/generic.py | 29 +++++++++++++++++------------
 tests/test_generic.py       |  4 ++++
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/sqlalchemy_utils/generic.py b/sqlalchemy_utils/generic.py
index f2855d2..e4aeb49 100644
--- a/sqlalchemy_utils/generic.py
+++ b/sqlalchemy_utils/generic.py
@@ -50,20 +50,25 @@ class GenericAttributeImpl(attributes.ScalarAttributeImpl):
         # Set us on the state.
         dict_[self.key] = initiator
 
-        # Get the primary key of the initiator and ensure we
-        # can support this assignment.
-        mapper = class_mapper(type(initiator))
-        if len(mapper.primary_key) > 1:
-            raise sa_exc.InvalidRequestError(
-                'Generic relationships against tables with composite '
-                'primary keys are not supported.')
+        if initiator is None:
+            # Nullify relationship args
+            dict_[self.parent_token.id.key] = None
+            dict_[self.parent_token.discriminator.key] = None
+        else:
+            # Get the primary key of the initiator and ensure we
+            # can support this assignment.
+            mapper = class_mapper(type(initiator))
+            if len(mapper.primary_key) > 1:
+                raise sa_exc.InvalidRequestError(
+                    'Generic relationships against tables with composite '
+                    'primary keys are not supported.')
 
-        pk = mapper.identity_key_from_instance(initiator)[1][0]
+            pk = mapper.identity_key_from_instance(initiator)[1][0]
 
-        # Set the identifier and the discriminator.
-        discriminator = table_name(initiator)
-        dict_[self.parent_token.id.key] = pk
-        dict_[self.parent_token.discriminator.key] = discriminator
+            # Set the identifier and the discriminator.
+            discriminator = table_name(initiator)
+            dict_[self.parent_token.id.key] = pk
+            dict_[self.parent_token.discriminator.key] = discriminator
 
 
 class GenericRelationshipProperty(MapperProperty):
diff --git a/tests/test_generic.py b/tests/test_generic.py
index c52a3ab..af94265 100644
--- a/tests/test_generic.py
+++ b/tests/test_generic.py
@@ -28,6 +28,10 @@ class TestGenericForiegnKey(TestCase):
         self.User = User
         self.Event = Event
 
+    def test_set_as_none(self):
+        event = self.Event()
+        event.object = None
+
     def test_set_manual_and_get(self):
         user = self.User()