Codeigniter - 清除缓存查询更新

Question

In my code, i use cache query to cache rows of info. Example: when member login, i will cache it. How can when user update, it only file of account? More example, i cache $id = 5, it will remove file of account have $id = 5

$this->db->cache_on();
$this->db->escape($id);
$this->db->where("username", $id);
$query = $this->db->get("unlock_user");
return $query->row_array();