Use separate label generator for column_label naming convention

Fixed bug where a table that would have a column label overlap with a plain
column name, such as "foo.id AS foo_id" vs. "foo.foo_id", would prematurely
generate the ``._label`` attribute for a column before this overlap could
be detected due to the use of the ``index=True`` or ``unique=True`` flag on
the column in conjunction with the default naming convention of
``"column_0_label"``.  This would then lead to failures when ``._label``
were used later to generate a bound parameter name, in particular those
used by the ORM when generating the WHERE clause for an UPDATE statement.
The issue has been fixed by using an alternate ``._label`` accessor for DDL
generation that does not affect the state of the :class:`.Column`.   The
accessor also bypasses the key-deduplication step as it is not necessary
for DDL, the naming is now consistently ``"<tablename>_<columnname>"``
without any subsequent numeric symbols when used in DDL.

Fixes: #4911

Change-Id: Iabf5fd3250738d800d6e41a2a3a27a7ce2405e7d

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index af538af0e..4e8f4a397 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -1434,7 +1434,12 @@ class Column(DialectKWArgs, SchemaItem, ColumnClause):
                     "To create indexes with a specific name, create an "
                     "explicit Index object external to the Table."
                 )
-            Index(None, self, unique=bool(self.unique), _column_flag=True)
+            table.append_constraint(
+                Index(
+                    None, self.key, unique=bool(self.unique), _column_flag=True
+                )
+            )
+
         elif self.unique:
             if isinstance(self.unique, util.string_types):
                 raise exc.ArgumentError(