/system/database/DB_cache.php 数据库缓存类

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.1.6 or newer
 *
 * @package		CodeIgniter
 * @author		ExpressionEngine Dev Team
 * @copyright	Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license		http://codeigniter.com/user_guide/license.html
 * @link		http://codeigniter.com
 * @since		Version 1.0
 * @filesource
 */

// ------------------------------------------------------------------------

/**
 * Database Cache Class
 * 数据库缓存类
 * 
 * @category	Database
 * @author		ExpressionEngine Dev Team
 * @link		http://codeigniter.com/user_guide/database/
 */
class CI_DB_Cache {

	var $CI;    //超级CI类
	
	var $db;	// allows passing of db object so that multiple database connections and returned db objects can be supported
    //允许通过db对象，使多个数据库连接并返回DB对象可以支持
	
	/**
	 * Constructor
	 *
	 * Grabs the CI super object instance so we can access it.
	 * 抓住CI超级对象实例，这样我们就可以访问它。
	 */
	function __construct(&$db)
	{
		// Assign the main CI object to 分配主要CI对象 $this->CI
		// and load the file helper since we use it a lot 并加载该文件，因为我们使用了很多帮手
		$this->CI =& get_instance();
		$this->db =& $db;
		$this->CI->load->helper('file'); //加载的是文件帮手类
	}

	// --------------------------------------------------------------------

	/**
	 * Set Cache Directory Path
	 * 设置缓存目录路径
	 * @access	public
	 * @param	string	the path to the cache directory 在高速缓存目录的路径...
	 * @return	bool
	 */
	function check_path($path = '')
	{
		//如果路径为空
		if ($path == '')
		{
			//如果当前的db->cachedir也为空值
			if ($this->db->cachedir == '')
			{
				return $this->db->cache_off(); //我干，cache_off()放在什么地方了，咱找不到，应该是返回cache的状态
			    //关闭缓存
			}
            //设置db类中的cachedir为$path路径
			$path = $this->db->cachedir;
		}

		// Add a trailing slash to the path if needed 如果需要添加尾随斜线路径
		//这句不懂，不做备注
		$path = preg_replace("/(.+?)\/*$/", "\\1/",  $path);

		//目录是否存在并且是否有定入权限
		if ( ! is_dir($path) OR ! is_really_writable($path))
		{
			// If the path is wrong we'll turn off caching
			// 如果路径是错误的，我们将关闭缓存
			return $this->db->cache_off();
		}
        //设置路径到db->cachedir中
		$this->db->cachedir = $path;
		return TRUE;
	}

	// --------------------------------------------------------------------

	/**
	 * Retrieve a cached query
	 * 检索缓存查询
	 * 
	 * The URI being requested will become the name of the cache sub-folder.
	 * An MD5 hash of the SQL statement will become the cache file name
	 * 所请求的URI，将成为高速缓存中的子文件夹的名称。
     * 的MD5哈希值的SQL语句，将成为高速缓存的文件名
     * 
	 * @access	public
	 * @return	string
	 */
	function read($sql)
	{
		//如果找不到缓存目录，直接关闭缓存
		if ( ! $this->check_path())
		{
			return $this->db->cache_off();
		}

		//uri->segment(1) 取得url的第一个参数,也就是处理器的名称
		$segment_one = ($this->CI->uri->segment(1) == FALSE) ? 'default' : $this->CI->uri->segment(1);

		//取得url的第二个参数，也就是处理函数的名称
		$segment_two = ($this->CI->uri->segment(2) == FALSE) ? 'index' : $this->CI->uri->segment(2);

		//然后用cachedir.$segment_one.'+'.$segment_two./md5($sql)名称
		$filepath = $this->db->cachedir.$segment_one.'+'.$segment_two.'/'.md5($sql);

		//如果没有读取到缓存内容，直接返回空
		if (FALSE === ($cachedata = read_file($filepath)))
		{
			return FALSE;
		}

		//然后返序列化返回
		//unserialize() unserialize()
		return unserialize($cachedata);
	}

	// --------------------------------------------------------------------

	/**
	 * Write a query to a cache file
	 * 写一个查询到缓存文件
	 * @access	public
	 * @return	bool
	 */
	function write($sql, $object)
	{
		if ( ! $this->check_path())
		{
			return $this->db->cache_off();
		}

		$segment_one = ($this->CI->uri->segment(1) == FALSE) ? 'default' : $this->CI->uri->segment(1);

		$segment_two = ($this->CI->uri->segment(2) == FALSE) ? 'index' : $this->CI->uri->segment(2);

		$dir_path = $this->db->cachedir.$segment_one.'+'.$segment_two.'/';

		$filename = md5($sql); //文件名

		//如果目录不存在
		if ( ! @is_dir($dir_path))
		{
			//如果创建目录失败,直接返回
			if ( ! @mkdir($dir_path, DIR_WRITE_MODE))
			{
				return FALSE;
			}
            //设置该目录的可写权限
			@chmod($dir_path, DIR_WRITE_MODE);
		}
		
        //将查询结果经过 serialize（）序列化放入到缓存文件中
        //file_helper.php function
		if (write_file($dir_path.$filename, serialize($object)) === FALSE)
		{
			return FALSE;
		}
        //然后设置该缓存文件的访问权限
		@chmod($dir_path.$filename, FILE_WRITE_MODE);
		return TRUE;
	}

	// --------------------------------------------------------------------

	/**
	 * Delete cache files within a particular directory
	 * 在一个特定的目录中删除缓存文件
	 * @access	public
	 * @return	bool
	 */
	function delete($segment_one = '', $segment_two = '')
	{
		if ($segment_one == '')
		{
			$segment_one  = ($this->CI->uri->segment(1) == FALSE) ? 'default' : $this->CI->uri->segment(1);
		}

		if ($segment_two == '')
		{
			$segment_two = ($this->CI->uri->segment(2) == FALSE) ? 'index' : $this->CI->uri->segment(2);
		}

		$dir_path = $this->db->cachedir.$segment_one.'+'.$segment_two.'/';

		delete_files($dir_path, TRUE); //file_helper.php function
	}

	// --------------------------------------------------------------------

	/**
	 * Delete all existing cache files
	 * 删除所有现有的缓存文件
	 * @access	public
	 * @return	bool
	 */
	function delete_all()
	{
		delete_files($this->db->cachedir, TRUE); //file_helper.php function
	}

}


/* End of file DB_cache.php */
/* Location: ./system/database/DB_cache.php */