From 61562e58435efddda19d15c61afd6e5326745a31 Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Wed, 18 Aug 2010 10:54:40 -0400
Subject: [PATCH] - object_session() raises the proper UnmappedInstanceError
 when presented with an unmapped instance.  [ticket:1881]

---
 CHANGES                       |  4 ++++
 lib/sqlalchemy/orm/session.py | 12 ++++++++++--
 test/orm/test_session.py      | 17 ++++++++++++++++-
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/CHANGES b/CHANGES
index 4f60857ef8..aae1139a14 100644
--- a/CHANGES
+++ b/CHANGES
@@ -100,6 +100,10 @@ CHANGES
     in some UNION situations, would fail to 
     propagate the inner columns completely to
     the outer query.  [ticket:1852]
+
+  - object_session() raises the proper 
+    UnmappedInstanceError when presented with an
+    unmapped instance.  [ticket:1881]
     
 - sql
   - Added basic math expression coercion for 
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index c67dc5553f..86d5dd7730 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -1674,9 +1674,17 @@ def make_transient(instance):
     
     
 def object_session(instance):
-    """Return the ``Session`` to which instance belongs, or None."""
+    """Return the ``Session`` to which instance belongs.
+    
+    If the instance is not a mapped instance, an error is raised.
 
-    return _state_session(attributes.instance_state(instance))
+    """
+    
+    try:
+        return _state_session(attributes.instance_state(instance))
+    except exc.NO_STATE:
+        raise exc.UnmappedInstanceError(instance)
+        
 
 def _state_session(state):
     if state.session_id:
diff --git a/test/orm/test_session.py b/test/orm/test_session.py
index 22de94e2b3..779db304e2 100644
--- a/test/orm/test_session.py
+++ b/test/orm/test_session.py
@@ -10,7 +10,8 @@ import sqlalchemy as sa
 from sqlalchemy.test import engines, testing, config
 from sqlalchemy import Integer, String, Sequence
 from sqlalchemy.test.schema import Table, Column
-from sqlalchemy.orm import mapper, relationship, backref, joinedload
+from sqlalchemy.orm import mapper, relationship, backref, joinedload, \
+    exc as orm_exc, object_session
 from sqlalchemy.test.testing import eq_
 from test.engine import _base as engine_base
 from test.orm import _base, _fixtures
@@ -67,6 +68,20 @@ class SessionTest(_fixtures.FixtureTest):
         finally:
             c.close()
 
+    @testing.resolve_artifact_names
+    def test_object_session_raises(self):
+        assert_raises(
+            orm_exc.UnmappedInstanceError,
+            object_session, 
+            object()
+        )
+
+        assert_raises(
+            orm_exc.UnmappedInstanceError,
+            object_session, 
+            User()
+        )
+        
     @testing.requires.sequences
     def test_sequence_execute(self):
         seq = Sequence("some_sequence")
-- 
2.47.2