将PHP的session数据存储到数据库中的代码实例

一个开发环境有多个网站，需要使用不同的session，解决方案很多。不过这次也高大上一把，用数据库存，方便以后扩展。

PostgreSQL版
首先是数据库的部分

    --drop table php_session
    create unlogged table php_session
    (
      sess_id varchar(32) primary key,
      modify_time timestamp with time zone not null,
      sess_data varchar(3000) default ''
    );

    create index concurrently idx_php_session_modify_time on php_session(modify_time);

    --set_session(id, data)
    create or replace function set_session(varchar, varchar) returns void as $set_session$
      with upsert as (
        update php_session
        set modify_time = current_timestamp, sess_data = $2
        where sess_id = $1
        returning 1
      )
      insert into php_session (sess_id, modify_time, sess_data)
      select $1, current_timestamp, $2
      where not exists (
        select 1 from upsert
      );
    $set_session$ language sql;

    --get_session(id)
    create or replace function get_session(varchar) returns varchar as $get_session$
      select sess_data from php_session where sess_id = $1
    $get_session$ language sql;

    --del_session
    create or replace function del_session(varchar) returns void as $del_session$
      delete from php_session where sess_id = $1
    $del_session$ language sql;

    --gc_session
    create or replace function gc_session() returns void as $del_session$
      delete from php_session where modify_time < current_timestamp - interval '30 days'
    $del_session$ language sql;

然后是PHP的部分

    <?php

    session_set_save_handler(
      function ($savePath, $sessionName) {//open
        return true;
      },
      function () {//close
        return true;
      },
      function ($id) {//read
        $sql = "select get_session($1)";
        $stmt = pg_query_params(SESSION_CONN, $sql, array($id));
        $result = pg_fetch_row($stmt);

        return $result[0];
      },
      function ($id, $data) {//write
        $sql = "select set_session($1, $2)";
        pg_query_params(SESSION_CONN, $sql, array($id, $data));
        return true;
      },
      function ($id) {//destroy
        $sql = "select del_session($1)";
        pg_query_params(SESSION_CONN, $sql, array($id, $data));
        return true;
      },
      function ($maxlifetime) {//gc
        //php needn't control the global session gc 
        return true;
      }
    );

    register_shutdown_function('session_write_close');

    ?>

然后只要在session_start之前调用这个就可以了

至于SESSION_CONN，那是我定义的一个常量，表示一个指向session数据库的链接而已。

MySQL版
再总结一个针对MySQL的集成更多基础功能的例子：
表结构：

     CREATE TABLE IF NOT EXISTS `sessioninfo` (
     `sid` varchar(255) NOT NULL,
     `value` text NOT NULL,
     `expiration` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
     PRIMARY KEY (`sid`)
     ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

session信息存储到数据库的类：

    class MySessionHandler implements SessionHandlerInterface {

      /**
      * @access private
      * @var object 数据库连接
      */
      private $_dbLink;
      /**
      * @access private
      * @var string 保存session的表名
      */
      Private $_sessionTable;
      /**
      * @access private
      * @var string session名
      */
      private $_sessionName;
      /**
      * @const 过期时间
      */
      const SESSION_EXPIRE = 10;

      public function __construct($dbLink, $sessionTable) {
        if(!is_object($dbLink)) {
          return false;
        }
        $this->_dbLink = $dbLink;
        $this->_sessionTable = $sessionTable;
      }

      /**
      * 打开
      * @access public
      * @param string $session_save_path 保存session的路径
      * @param string $session_name session名
      * @return integer
      */
      public function open($session_save_path, $session_name) {
        $this->_sessionName = $session_name;
        return 0;
      }

      /**
      * 关闭
      * @access public
      * @return integer
      */
      public function close() {
        return 0;
      }

      /**
      * 关闭session
      * @access public
      * @param string $session_id session ID
      * @return string
      */
      public function read($session_id) {
        $query = "SELECT value FROM {$this->_sessionTable} WHERE sid = {$session_id} AND UNIX_TIMESTAMP(expiration) + " . self::SESSION_EXPIRE . " > UNIX_TIMESTAMP(NOW())";
        $result = $this->_dbLink->query($query);
        if(!isset($value) || empty($value)) {
          $value = "";
          return $value;
        }
        $this->_dbLink->query("UPDATE {$this->_sessionTable} SET expiration = CURRENT_TIMESTAMP() WHERE sid = {$session_id}");
        $value = $result->fetch_array();
        $result->free();
        return $value['value'];
      }

      /**
      * 写入session
      * @access public
      * @param string $session_id session ID
      * @param string $session_data session data
      * @return integer
      */
      public function write($session_id, $session_data) {
        $query = "SELECT value FROM {$this->_sessionTable} WHERE sid = '{$session_id}' AND UNIX_TIMESTAMP(expiration) + " . self::SESSION_EXPIRE . " > UNIX_TIMESTAMP(NOW())";
        $result = $this->_dbLink->query($query);
        $result = $result->fetch_array();
        if(!empty($result)) {
          $result = $this->_dbLink->query("UPDATE {$this->_sessionTable} SET value = {$session_data} WHERE sid = {$session_id}");
        }
        else{
          $result = $this->_dbLink->query("INSERT INTO {$this->_sessionTable} (sid, value) VALUES ('{$session_id}', '{$session_data}')");
        }
        if($result){
          return 0;
        }
        else{
          return 1;
        }    
      }

      /**
      * 销魂session
      * @access public
      * @param string $session_id session ID
      * @return integer
      */
      public function destroy($session_id) {
        $result = $this->_dbLink->query("DELETE FROM {$this->_sessionTable} WHERE sid = '{$session_id}'");
        if($result){
          return 0;
        }
        else{
          return 1;
        }
      }

      /**
      * 垃圾回收
      * @access public
      * @param string $maxlifetime session 最长生存时间
      * @return integer
      */
      public function gc($maxlifetime) {
        $result = $this->_dbLink->query("DELETE FROM {$this->_sessionTable} WHERE UNIX_TIMESTAMP(expiration) < UNIX_TIMESTAMP(NOW()) - " . self::SESSION_EXPIRE);
        if($result){
          return 0;
        }
        else{
          return 1;
        }
      }

    }

    $dbLink = new mysqli("localhost", "root", "root", "test");
    $sessionTable = "sessioninfo";

    $handler = new MySessionHandler($dbLink, $sessionTable);
    session_set_save_handler($handler);
    session_start();
    $_SESSION['name'] = "test";
    echo $_SESSION["name"];
    //session_destroy();