【opencart3源码分析】数据库缓存类db.php

<?php
/*
CREATE TABLE IF NOT EXISTS `session` (
  `session_id` varchar(32) NOT NULL,
  `data` text NOT NULL,
  `expire` datetime NOT NULL,
  PRIMARY KEY (`session_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;
*/
namespace Session;
/**
 * 数据库缓存类
 * @package Session
 */
final class DB {
    // 过期时间
	public $expire = '';
	// 构造方法
	public function __construct($registry) {
	    // 注册实例
		$this->db = $registry->get('db');
		// 设置最大生命周期
		$this->expire = ini_get('session.gc_maxlifetime');
	}

	// 读取缓存
	public function read($session_id) {
		$query = $this->db->query("SELECT `data` FROM `" . DB_PREFIX . "session` WHERE session_id = '" . $this->db->escape($session_id) . "' AND expire > '" . $this->db->escape(date('Y-m-d H:i:s', time()))  . "'");
		
		if ($query->num_rows) {
			return json_decode($query->row['data'], true);
		} else {
			return false;
		}
	}

	// 写入缓存
	public function write($session_id, $data) {
		if ($session_id) {
			$this->db->query("REPLACE INTO `" . DB_PREFIX . "session` SET session_id = '" . $this->db->escape($session_id) . "', `data` = '" . $this->db->escape(json_encode($data)) . "', expire = '" . $this->db->escape(date('Y-m-d H:i:s', time() + $this->expire)) . "'");
		}
		
		return true;
	}

	// 销毁指定id缓存
	public function destroy($session_id) {
		$this->db->query("DELETE FROM `" . DB_PREFIX . "session` WHERE session_id = '" . $this->db->escape($session_id) . "'");
		
		return true;
	}

	// 销毁过期缓存
	public function gc($expire) {
		$this->db->query("DELETE FROM `" . DB_PREFIX . "session` WHERE expire < '" . $this->db->escape(date('Y-m-d H:i:s', time())) . "'");
		
		return true;
	}
}