ignore and warn for native_enum=False with pg.ENUM datatype

any UPPERCASE datatype refers to that exact type name rendered
on the database.   So PG's ENUM must render "ENUM" and is
"native" by definition.  warn if this flag is passed.

The :class:`_postgresql.ENUM` datatype is PostgreSQL-native and therefore
should not be used with the ``native_enum=False`` flag. This flag is now
ignored if passed to the :class:`_postgresql.ENUM` datatype and a warning
is emitted; previously the flag would cause the type object to fail to
function correctly.

Fixes: #6106
Change-Id: I08e0ec6fcfafd068e1eaf6aec13c8010f09ce94a

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 82b848ece..f33542ee8 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -1868,6 +1868,14 @@ class ENUM(sqltypes.NativeForEmulated, sqltypes.Enum):
          be used to emit SQL to a target bind.
 
         """
+        native_enum = kw.pop("native_enum", None)
+        if native_enum is False:
+            util.warn(
+                "the native_enum flag does not apply to the "
+                "sqlalchemy.dialects.postgresql.ENUM datatype; this type "
+                "always refers to ENUM.   Use sqlalchemy.types.Enum for "
+                "non-native enum."
+            )
         self.create_type = kw.pop("create_type", True)
         super(ENUM, self).__init__(*enums, **kw)