On-demand data retrieval between memcached and mysql in Codeigniter

query_cache.php

/**
 *
 * query_cache
 *
 * 查询缓存，返回数据集。如果缓存不存在或系统不支持缓存，则直接从model中提取。
 *
 *
 * @param	string  $key	Key of the cache item
 * @param	string	$model	Model name from which we retrieve data
 * @param	string	$method Method name of such model
 * @param	array	$params	Params given to such method 
 * @param	int	$ttl	time to live of the cache item (in seconds)
 * @return	mixed	Cached data
 */
function query_cache($key, $model, $method, $params = array(), $ttl = 1296000)
{
        $CI = & get_instance();

	// Required model not loaded?
	// Load models on demand
	if( ! in_array($model, $CI->load->_ci_models, TRUE))
	{
		$CI->load->model($model);
	}
	
	// Ref this model
	$handler = & $CI->$model;
	
	// Cache is disabled when we are in DEV or other unkonwn situations
	if( ! $CI->cache->memcached->is_supported())
	{
		return call_user_func_array(array($handler, $method), $params);
	}
	
	// Valid cache item? If so, we've done!
	if( ! $data = $CI->cache->memcached->get($key))
	{
		// Fetch data from model
		$data = call_user_func_array(array($handler, $method), $params);
		
		// WARINING: EMPTY results (such as 0, FALSE) may be ignored!
		if( ! empty($data))
		{
			// Make the results cacheable!
			$CI->cache->memcached->save($key, $data, $ttl);
		}
	}
	
	return $data;
}