added to_selectable() onto ColumnClause to simplify _get_col_by_original

diff --git a/lib/sqlalchemy/sql.py b/lib/sqlalchemy/sql.py
index 45a95795fe3e6c18f141439ced810ccd262dff05..34f59fd9ccbaaa8b7dfc0e72be00d14904328eaf 100644 (file)
--- a/lib/sqlalchemy/sql.py
+++ b/lib/sqlalchemy/sql.py
@@ -1033,6 +1033,12 @@ class ColumnClause(ColumnElement):
     _label = property(_get_label)
     def accept_visitor(self, visitor): 
         visitor.visit_column(self)
+    def to_selectable(self, selectable):
+        """given a Selectable, returns this column's equivalent in that Selectable, if any.
+        
+        for example, this could translate the column "name" from a Table object
+        to an Alias of a Select off of that Table object."""
+        return selectable._get_col_by_original(self.original, False)
     def _get_from_objects(self):
         if self.table is not None:
             return [self.table]