- fixed bug which was preventing UNIONS from being cloneable,

[ticket:986]

2 files changed, 17 insertions, 8 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 56629a6ca..812c70c2d 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -2925,8 +2925,6 @@ class CompoundSelect(_SelectBaseMixin, FromClause):
             else:
                 self.selects.append(s)
 
-        self._col_map = {}
-
         _SelectBaseMixin.__init__(self, **kwargs)
 
         for s in self.selects:
@@ -2942,11 +2940,15 @@ class CompoundSelect(_SelectBaseMixin, FromClause):
                 yield c
 
     def _proxy_column(self, column):
-        selectable = column.table
-        col_ordering = self._col_map.get(selectable, None)
-        if col_ordering is None:
-            self._col_map[selectable] = col_ordering = []
-
+        if not hasattr(self, '_col_map'):
+            self._col_map = dict([(s, []) for s in self.selects])
+            for s in self.selects:
+                for c in s.c + [s.oid_column]:
+                    self._col_map[c] = s
+        
+        selectable = self._col_map[column]
+        col_ordering = self._col_map[selectable]
+        
         if selectable is self.selects[0]:
             if self.use_labels:
                 col = column._make_proxy(self, name=column._label)
@@ -2962,8 +2964,9 @@ class CompoundSelect(_SelectBaseMixin, FromClause):
 
     def _copy_internals(self, clone=_clone):
         self._clone_from_clause()
-        self._col_map = {}
         self.selects = [clone(s) for s in self.selects]
+        if hasattr(self, '_col_map'):
+            del self._col_map
         for attr in ('_order_by_clause', '_group_by_clause'):
             if getattr(self, attr) is not None:
                 setattr(self, attr, clone(getattr(self, attr)))
diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index 70a1dcc96..9954811d6 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -152,6 +152,12 @@ class AbstractClauseProcessor(object):
 
     This class implements its own visit-and-copy strategy but maintains the
     same public interface as visitors.ClauseVisitor.
+    
+    The convert_element() method receives the *un-copied* version of each element.
+    It can return a new element or None for no change.  If None, the element
+    will be cloned afterwards and added to the new structure.  Note this is the
+    opposite behavior of visitors.traverse(clone=True), where visitors receive
+    the cloned element so that it can be mutated.
     """
 
     __traverse_options__ = {'column_collections':False}