[1.2.X] Fixed #13668 -- Corrected database router methods invocation for ManyToMany fields without through models. Thanks craig.kimerer for the report and David Gouldin for the fix.

This also adds tests for r14857.

Backport of [15185] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15186 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/multiple_database/tests.py

@@ -1679,3 +1679,56 @@ class PickleQuerySetTestCase(TestCase):
             Book.objects.using(db).create(title='Dive into Python', published=datetime.date(2009, 5, 4))
             qs = Book.objects.all()
             self.assertEqual(qs.db, pickle.loads(pickle.dumps(qs)).db)
+
+class AttributeErrorRouter(object):
+    "A router to test the exception handling of ConnectionRouter"
+    def db_for_read(self, model, **hints):
+        raise AttributeError
+
+    def db_for_write(self, model, **hints):
+        raise AttributeError
+
+class RouterAttributeErrorTestCase(TestCase):
+    multi_db = True
+
+    def setUp(self):
+        self.old_routers = router.routers
+        router.routers = [AttributeErrorRouter()]
+
+    def tearDown(self):
+        router.routers = self.old_routers
+
+    def test_attribute_error(self):
+        "Check that the AttributeError from AttributeErrorRouter bubbles up"
+        dive = Book()
+        dive.title="Dive into Python"
+        dive.published = datetime.date(2009, 5, 4)
+        self.assertRaises(AttributeError, dive.save)
+
+class ModelMetaRouter(object):
+    "A router to ensure model arguments are real model classes"
+    def db_for_write(self, model, **hints):
+        if not hasattr(model, '_meta'):
+            raise ValueError
+
+class RouterM2MThroughTestCase(TestCase):
+    multi_db = True
+
+    def setUp(self):
+        self.old_routers = router.routers
+        router.routers = [ModelMetaRouter()]
+
+    def tearDown(self):
+        router.routers = self.old_routers
+
+    def test_m2m_through(self):
+        b = Book.objects.create(title="Pro Django",
+                                published=datetime.date(2008, 12, 16))
+
+        p = Person.objects.create(name="Marty Alchin")
+        # test add
+        b.authors.add(p)
+        # test remove
+        b.authors.remove(p)
+        # test clear
+        b.authors.clear()