public ActionResult<Magazine> Checkout(int magazineId)
 {
   try
   {
     Magazine magazineToCheckout = _ms.Get(magazineId);
     if (magazineToCheckout == null) { throw new Exception("Invalid ID"); }
     magazineToCheckout.Available = false;
     return Ok(_ms.CheckOut(magazineToCheckout));
   }
   catch (Exception e)
   {
     return BadRequest(e.Message);
   }
 }//endof checkout