Use cache class

in previous post, i introduced the technical to cache a objec to file
And in this post, i continue introduce to way to use it.
The fist : thinking the id for cache, this id must be unique, example I have class person and do the list method  in this class at page 2 in default module.

The best id is ="default_person_list_2"
so we have $cache_key ="default_person_list_2"

class person{
 public function list() {
        $cache_key ='default_person_list_2';
       include 'caches.php';
        $cache =new cache();
        if ($cache->isValid($cache_key))
        {
            $result = $cache->getCache($cache_key);
        }
        else
        {
             $person_db = new person_db();
            
              $result = $person_db ->getAll();
              $result =$result;
              $cache->save($cache_key, __CACHE_TIME, $result);
        }
        
     // do something continue.
    }
}

we include caches class and create new object caches.
the first: we check valid long life . if it is still valid then we get result from cache.
Otherwise, we get result from db throught $person_db (or some class else) and cache the result to file.
And if have second request, we will not get result from db again.