Sourced from alembic's releases.

1.20.1

Released: October 21, 2026

bug

• [bug] [autogenerate] Fixed issue where a table or column comment set to an empty string would cause autogenerate to detect a comment change on every run. As most backends, including PostgreSQL, MySQL, MariaDB and Oracle, don't store an empty string comment distinctly from no comment, autogenerate now treats an empty string comment the same as None when comparing comments. Additionally, an empty string comment is now rendered in op.create_table() and op.add_column() directives, where it was previously omitted. Pull request courtesy vineoy.

  References: #1085

• [bug] [autogenerate] [postgresql] Fixed rendering of the PostgreSQL ~sqlalchemy.dialects.postgresql.DOMAIN type in autogenerated migration scripts. Previously the type was rendered using repr(), which omitted the check, not_null, default, collation, constraint_name, schema and create_type arguments and did not apply a dialect prefix to the underlying data type. The full set of arguments is now rendered and the underlying data type is rendered using the standard type-rendering logic. Pull request courtesy Sebastian Cao.

  References: #1360

• [bug] [autogenerate] [postgresql] Fixed false-positive "Computed default cannot be modified" warning emitted during autogenerate when comparing PostgreSQL Computed columns whose reflected SQL expression includes type cast specifiers such as ::regconfig or ::text, which PostgreSQL adds to the expression as stored. These cast specifiers are now stripped before comparison so that otherwise equivalent expressions no longer trigger the warning. Pull request courtesy Sebastian Cao.

  References: #1462

• [bug] [autogenerate] [postgresql] Fixed issue where autogenerate would detect an unchanged PostgreSQL expression-based index as modified when the expression included type casts, such as a cast to a type with a length or precision, a nested cast, or a cast followed by a DESC modifier.

• [bug] [postgresql] Fixed bug where Operations.alter_column() against a PostgreSQL identity column would render an incomplete, invalid ALTER TABLE ... ALTER COLUMN statement with no clause at all when existing_server_default was omitted, even if there were no existing server default. Pull request courtesy Riti Grover.

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