Repair _orm_columns() to accommodate text()

Fixed bug whereby passing a :func:`.text` construct to the
:meth:`.Query.group_by` method would raise an error, instead
of intepreting the object as a SQL fragment.

Change-Id: I5fc2f590b76508d52e23b5fa9cf037ddea8080c3
fixes: #3706

2 files changed, 3 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/base.py b/lib/sqlalchemy/orm/base.py
index 7947cd7d7..8d86fb24e 100644
--- a/lib/sqlalchemy/orm/base.py
+++ b/lib/sqlalchemy/orm/base.py
@@ -344,7 +344,7 @@ def _attr_as_key(attr):
 
 def _orm_columns(entity):
     insp = inspection.inspect(entity, False)
-    if hasattr(insp, 'selectable'):
+    if hasattr(insp, 'selectable') and hasattr(insp.selectable, 'c'):
         return [c for c in insp.selectable.c]
     else:
         return [entity]
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 00c2c37ba..e0367f967 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -1206,6 +1206,8 @@ class TextClause(Executable, ClauseElement):
 
     @property
     def selectable(self):
+        # allows text() to be considered by
+        # _interpret_as_from
         return self
 
     _hide_froms = []