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, 11 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index c6c30629d..5ecec7d6c 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -3022,6 +3022,10 @@ class DDLCompiler(Compiled):
         text = "CREATE "
         if index.unique:
             text += "UNIQUE "
+        if index.name is None:
+            raise exc.CompileError(
+                "CREATE INDEX requires that the index have a name"
+            )
         text += "INDEX %s ON %s (%s)" % (
             self._prepared_index_name(index, include_schema=include_schema),
             preparer.format_table(
@@ -3038,6 +3042,11 @@ class DDLCompiler(Compiled):
 
     def visit_drop_index(self, drop):
         index = drop.element
+
+        if index.name is None:
+            raise exc.CompileError(
+                "DROP INDEX requires that the index have a name"
+            )
         return "\nDROP INDEX " + self._prepared_index_name(
             index, include_schema=True
         )
@@ -3251,7 +3260,8 @@ class DDLCompiler(Compiled):
         text = ""
         if constraint.name is not None:
             formatted_name = self.preparer.format_constraint(constraint)
-            text += "CONSTRAINT %s " % formatted_name
+            if formatted_name is not None:
+                text += "CONSTRAINT %s " % formatted_name
         text += "UNIQUE (%s)" % (
             ", ".join(self.preparer.quote(c.name) for c in constraint)
         )