fix declarative

1 files changed, 4 insertions, 3 deletions

diff --git a/lib/sqlalchemy/ext/declarative.py b/lib/sqlalchemy/ext/declarative.py
index 2310f01ce..dc7e5feb4 100755
--- a/lib/sqlalchemy/ext/declarative.py
+++ b/lib/sqlalchemy/ext/declarative.py
@@ -1151,12 +1151,13 @@ class _GetColumns(object):
         
         mapper = class_mapper(self.cls, compile=False)
         if mapper:
-            prop = mapper.get_property(key, raiseerr=False)
-            if prop is None:
+            if not mapper.has_property(key):
                 raise exceptions.InvalidRequestError(
                             "Class %r does not have a mapped column named %r"
                             % (self.cls, key))
-            elif not isinstance(prop, ColumnProperty):
+                            
+            prop = mapper.get_property(key)
+            if not isinstance(prop, ColumnProperty):
                 raise exceptions.InvalidRequestError(
                             "Property %r is not an instance of"
                             " ColumnProperty (i.e. does not correspond"