Every person elected or appointed to an office in the City shall, within twenty days after his election or appointment and before he shall enter upon the duties of his office, take and subscribe to the oath of office prescribed for district officers, which may be done before any person authorized by law to administer oaths or before the Mayor or Recorder of the City. The oath, together with the certificate of the officer administering the same, shall be filed, recorded and preserved in the office of the Recorder of the City, and a certified copy of such oath and certificate shall be filed and recorded in the office of the Clerk of the County Court.