how to enable caching with memcached?

XPDO_OPT_CACHE_DB => true

class LTC extends xPDO {
    function __construct() {    
        
        $this->_loadConfig();
        $this->config = array_merge(array(
            XPDO_OPT_CACHE_DB => $this->config['db_cache'],
            XPDO_OPT_CACHE_PATH => $this->config['lib_path'].'cache/',
            XPDO_OPT_HYDRATE_FIELDS => true,
            XPDO_OPT_HYDRATE_ADHOC_FIELDS => true,
            XPDO_OPT_HYDRATE_RELATED_OBJECTS => true,
            XPDO_OPT_TABLE_PREFIX => '',
            XPDO_OPT_VALIDATOR_CLASS => 'validation.iltcvalidator',
            XPDO_OPT_VALIDATE_ON_SAVE => true,
        ),$this->config);

       $host = $this->config['db_type'] .
                ':host='.$this->config['db_host'] .
                ';dbname='.$this->config['db_name'];
	parent::__construct(
		$host,
		$this->config['db_user'],
		$this->config['db_pass'],
		$this->config,
		array(
			PDO_ATTR_ERRMODE => PDO_ERRMODE_SILENT,
			PDO_ATTR_PERSISTENT => false,
			PDO_MYSQL_ATTR_USE_BUFFERED_QUERY => true
		));

	$this->setPackage('ltc',$this->config['lib_path'].'/model/');
    }

   ...

    function getCacheManager$class = 'cache.xPDOCacheManager') {
        if (isset($this->config['cache_disabled']) && $this->config['cache_disabled']) {
            $this->_cacheEnabled = false;
            return null;
        }
        if ($this->cacheManager === null) {
            if ($this->loadClass($class, XPDO_CORE_PATH, true, true)) {
                // can override the cache manager, if you want
                $cacheManagerClass = isset($this->config['CacheManager.class']) ? $this->config['CacheManager.class'] : 'cache.ltcCacheManager';
                if ($className = $this->loadClass($cacheManagerClass, '', false, true)) {
                    if ($this->cacheManager = new $className($this)) {
                        $this->_cacheEnabled = true;
                    }
                } else {
                    $this->_log(XPDO_LOG_LEVEL_FATAL,sprintf($ltc->lexicon['cachemanager_err_nf'],$class));
                }
            }
        }
        return $this->cacheManager;
    }
}

class MyXPDO extends xPDO
{
    function __construct($dsn, $username= '', $password= '', $tablePrefix= '', $driverOptions= null) 
	{
		parent::__construct($dsn, $username, $password, $tablePrefix, $driverOptions);

		// set the name of the caching system to use to Memcache.
		$this->config = array_merge(array('cache_db_handler' => 'Memcache'), $this->config);

		// connect to the cache manager.
		if ($cacheManager = $this->getCacheManager())
			$cacheManager->objcache->connect('10.0.0.1', 11211);
	}
}

  // retrieve user and cache their object for half an hour
  $user = $xpdo->get('User', array('id' => $modx->getUserLoginID()), 1800);

<?php
class MyXPDO extends xPDO {
    function __construct($dsn, $username= '', $password= '', $options= array(), $driverOptions= null) {
        // set the name of the caching system to use to Memcache.
        $options[XPDO_OPT_DB_CACHE_HANDLER]= 'Memcache';

        parent::__construct($dsn, $username, $password, $options, $driverOptions);

        // connect to the cache manager.
        if ($this->getCacheManager()) {
            $this->cacheManager->objcache->connect('10.0.0.1', 11211);
	}
}
?>

// snippet to return latest articles
include_once(/path/to/MyXPDO.class.php)
$xpdo = $MyXPDO();

echo getRecentArticles($xpdo, 5);

// params are an xPDO object, and the number of recent articles to return
function getRecentArticles($xpdo, $num)
{
	// we can't cache this using xPDO directly since we aren't retrieving an object. So we'll do it ourselves.
	// first, check whether there is data in the cache
	if($cacheManager = $xpdo->getCacheManager())
	{
		// creating a key like this means a unique key will be created depending on the parameters the function was called with.
		$key = md5('blogs::getRecentArticles: num: '.$num);
		
		// if the html isn't already in the cache, set a flag so we can cache the result after generating it.
		if ($html = $cacheManager->get($key))
		{
			return $html;
		}
		else
		{
			$inCache = false;
		}
	}

	// not in the cache, so perform query, then cache the final output
	$sql = 'SELECT ...';
	// process and format output and put it in $html
	$html = ...

	if (is_object($cacheManager) && !$inCache)
		$cacheManager->set($key, $html, 1800);

	return $html;
}