from typing import Any, cast

from sqlalchemy import types

from sqlalchemy.engine.interfaces import Dialect

class AutoString(types.TypeDecorator): # type: ignore

impl = types.String

cache_ok = True

mysql_default_length = 255

def load_dialect_impl(self, dialect: Dialect) -> "types.TypeEngine[Any]":

impl = cast(types.String, self.impl)

if impl.length is None and dialect.name == "mysql":

return dialect.type_descriptor(types.String(self.mysql_default_length))

return super().load_dialect_impl(dialect)