- Improved an error message which would occur if a query() were made

against a non-selectable, such as a :func:`.literal_column`, and then
an attempt was made to use :meth:`.Query.join` such that the "left"
side would be determined as ``None`` and then fail.  This condition
is now detected explicitly.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 81be0e63c..0f5b8bf88 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -1843,6 +1843,12 @@ class Query(object):
             elif self._entities:
                 left = self._entities[0].entity_zero_or_selectable
 
+        if left is None:
+            raise sa_exc.InvalidRequestError(
+                            "Don't know how to join from %s; please use "
+                            "select_from() to establish the left "
+                            "entity/selectable of this join" % self._entities[0])
+
         if left is right and \
                 not create_aliases:
             raise sa_exc.InvalidRequestError(