/// 只更新storedAddress數據中的DefaultAddress字段,更新為false

         /// 將默認地址改為不是默認地址

          /// </summary>

          /// <param name="id">需要修改的對象的id</param>

          public void Update(int id)

          {

              StoredAddress s = new StoredAddress { StoredAddressID = id };

             object originalItem = null;

             System.Data.EntityKey key = _context.CreateEntityKey("StoredAddresses", s);

             if (_context.TryGetObjectByKey(key, out originalItem))

             {

                 _context.Detach(originalItem);

             }

              s.DefaultAddress = true;

              _context.StoredAddresses.Attach(s);  

              s.DefaultAddress = false;            

              _context.SaveChanges();

              _context.Detach(s);

         }