[incomplete]Memcached Element and ElementList auto version control [占位]

This is my 1st version, maybe i can use getMulti and setMulti refactor it(优化之).

class CacheUtils {
    const CACHE_MAX_VERSION = 10;

    private $memcache;

    private static $instance;

    private function __construct() {
        $this->memcache = new Memcache();
        $this->memcache->connect('127.0.0.1', 11211) or die('Can not connect to memcached server.');
    }

    public static function getInstance() {
        if(self::$instance == null) {
            self::$instance = new CacheUtils();
        }
        return self::$instance;
    }

    public function addElementVersion($type) {
        $key = 'Element_Version:'.$type;
        $ver = $this->memcache->increment($key);
        if ($ver == false) {
            $ver = $this->memcache->set($key, 0);
            $ver = $this->memcache->increment($key);
        }
        else if ($ver > self::CACHE_MAX_VERSION) {
            // flush all! keep data correct
            $this->memcache->flush();
        }
        return $ver;
    }

    public function getElementVersion($type) {
        $key = 'Element_Version:'.$type;
        return $this->memcache->get($key);
    }

    public function addElement($elem) {
        $key = 'Element:'.$elem->type.':'.$elem->id;
        $retE = $this->memcache->set($key, $elem);
        $retV = $this->addElementVersion($elem->type);
        return $retE && $retV;
    }

    public function getElement($type, $id) {
        $key = 'Element:'.$type.':'.$id;
        return $this->memcache->get($key);
    }

    public function getElementListVersion($type, $sql) {
        $key = 'Element_List_Version:'.$type.':'.$sql;
        return $this->memcache->get($key);
    }


    public function addElementList($type, $list, $sql = '') {
        $keyList = 'Element_List:'.$type.':'.$sql;
        $keyVersion = 'Element_List_Version:'.$type.':'.$sql;

        $ver = $this->getElementVersion($type);
        $retL = $this->memcache->set($keyList, $list);
        $retV = $this->memcache->set($keyVersion, $ver);

        return $retL && $retV;
    }

    public function getElementList($type, $sql = '') {
        $keyList = 'Element_List:'.$type.':'.$sql;

        $elementVersion = $this->getElementVersion($type);
        $elementListVersion = $this->getElementListVersion($type, $sql);
        if ($elementListVersion != $elementVersion)
            return false;
        else
            return $this->memcache->get($keyList);
    }
}

Test Case:

<?php
require_once 'PHPUnit/Framework.php';

require_once dirname(__FILE__).'/../CacheUtils.php';

class Person {
    public $id;
    public $name;
    public $age;

    public $createTime;
    public $type;

    function __construct($id, $name, $age) {
        $this->id = $id;
        $this->name = $name;
        $this->age = $age;

        $this->type = get_class($this);
        $this->createTime = time();
    }
}

/**
 * Test class for CacheFacade.
 * Generated by PHPUnit on 2010-03-28 at 04:07:43.
 */
class CacheUtilsTest extends PHPUnit_Framework_TestCase {
    /**
     * testAddElement
     */
    public function testAddAndGetElement() {
        $cacheUtils = CacheUtils::getInstance();

        $person = new Person(101,'Linx', 29);
        $this->assertEquals(true, $cacheUtils->addElement($person));

        $personGet = $cacheUtils->getElement('Person', 101);
        $this->assertEquals('Linx', $personGet->name);
        var_dump($personGet);

    }

    public function testAddAndGetElementList() {
        $cacheUtils = CacheUtils::getInstance();

        $person1 = new Person(101,'Linx1', 29);
        $person2 = new Person(102,'Linx2', 30);
        $list = array($person1, $person2);

        $this->assertEquals(true, $cacheUtils->addElementList('Person', $list));

        $listGet = $cacheUtils->getElementList('Person');
        $this->assertEquals(2, count($listGet));
        $this->assertEquals('Linx1', $listGet[0]->name);

        var_dump($listGet);
    }

    public function testAddAndGetElementListExpired() {
        $cacheUtils = CacheUtils::getInstance();

        $person1 = new Person(101,'Linx1', 29);
        $person2 = new Person(102,'Linx2', 30);
        $list = array($person1, $person2);

        $this->assertEquals(true, $cacheUtils->addElementList('Person', $list));

        // Person v2
        $this->assertEquals(true, $cacheUtils->addElement($person1));

        // v1 is expired
        $listGet = $cacheUtils->getElementList('Person');
        $this->assertEquals(false, $listGet);

        var_dump($listGet);
    }


}
?>