- The :meth:`.PropComparator.of_type` modifier has been

improved in conjunction with loader directives such as
:func:`.joinedload` and :func:`.contains_eager` such that if
two :meth:`.PropComparator.of_type` modifiers of the same
base type/path are encountered, they will be joined together
into a single "polymorphic" entity, rather than replacing
the entity of type A with the one of type B.  E.g.
a joinedload of ``A.b.of_type(BSub1)->BSub1.c`` combined with
joinedload of ``A.b.of_type(BSub2)->BSub2.c`` will create a
single joinedload of ``A.b.of_type((BSub1, BSub2)) -> BSub1.c, BSub2.c``,
without the need for the ``with_polymorphic`` to be explicit
in the query.
fixes #3256

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/sqlalchemy/util/_collections.py b/lib/sqlalchemy/util/_collections.py
index a1fbc0fa0..d36852698 100644
--- a/lib/sqlalchemy/util/_collections.py
+++ b/lib/sqlalchemy/util/_collections.py
@@ -10,9 +10,10 @@
 from __future__ import absolute_import
 import weakref
 import operator
-from .compat import threading, itertools_filterfalse
+from .compat import threading, itertools_filterfalse, string_types
 from . import py2k
 import types
+import collections
 
 EMPTY_SET = frozenset()
 
@@ -779,10 +780,12 @@ def coerce_generator_arg(arg):
 def to_list(x, default=None):
     if x is None:
         return default
-    if not isinstance(x, (list, tuple)):
+    if not isinstance(x, collections.Iterable) or isinstance(x, string_types):
         return [x]
-    else:
+    elif isinstance(x, list):
         return x
+    else:
+        return list(x)
 
 
 def to_set(x):