EF 只更新部分字段

 /// 只更新storedAddress数据中的DefaultAddress字段,更新为false
         /// 将默认地址改为不是默认地址
          /// </summary>
          /// <param name="id">需要修改的对象的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);
         }