def change_username(self, user: User, new_username: str) -> None:
with self._session_cm as scm:
user.username = new_username
scm.session.commit()
def change_username(self, user: User, new_username: str) -> None:
# Update the mapping from username to user id
del self._user_id_map[user.username]
self._user_id_map[new_username] = user.id
user.username = new_username