MySql based session mangagement in PHP

<?php
	// Start the session ...
	session_start();

	// ... and assign some values. (The session will be created if not exists).
	$_SESSION['name'] = 'bornageek';
	$_SESSION['time'] = time();

	// Get a session value ...
	echo $_SESSION['name'] . 'logged in at ' . date('d.m.Y H:i:s', $_SESSION['time']);

	// ... and finally destroy the session.
	session_destroy();
?>

interface SessionManager {
     public function _open($save_path, $session_name);
     public function _close();
     public function _read($id);
     public function _write($id, $sess_data);
     public function _destroy($id);
     public function _gc($maxlifetime);
}

<?php

/**
 * The MySqlSession class implements all methods to use a
 * database based session management instead of using text files.
 * This has the benefit that all session data can be accessed
 * at a central place. This class is supported since the PHP version 5.0.5
 * because it uses the register_shutdown_function() function to ensure that
 * all session values are stored before the PHP representation is destroyed.
 *
 * @package SessionManager
 * @subpackage MySqlSession
 * @version 1.0
 * @date 09/04/2013
 * @author Andreas Schickedanz <info@bornageek.com>
 * @copyright Andreas Schickedanz
 * @link https://www.bornageek.com
 */
class MySqlSession implements SessionManager {
    /**
     * @var pdo $pdo The PDO object used to access the database
     * @access private
     */
    private $pdo = null;</info@bornageek.com>

    /**
     * Sets the user-level session storage functions which are used
     * for storing and retrieving data associated with a session.
     *
     * @access public
     * @param pdo $pdo The PDO object used to access the database
     * @return void
     */
    public function __construct(pdo $pdo) {
        // Assign the pdo object, ...
        $this->pdo = $pdo;

		    // ... change the ini configuration, ...
        ini_set('session.save_handler', 'user');

        // ... set the session handler to the class methods ...
        session_set_save_handler(
            array(&$this, '_open'),
            array(&$this, '_close'),
            array(&$this, '_read'),
            array(&$this, '_write'),
            array(&$this, '_destroy'),
            array(&$this, '_gc')
        );

        // ... and start a new session.
        session_start();

        // Finally ensure that the session values are stored.
        register_shutdown_function('session_write_close');
    }

    /**
     * Is called to open a session. The method
     * does nothing because we do not want to write
     * into a file so we don't need to open one.
     *
     * @access public
     * @param String $save_path The save path
     * @param String $session_name The name of the session
     * @return Boolean
     */
    public function _open($save_path, $session_name) {
        return true;
    }

    /**
     * Is called when the reading in a session is
     * completed. The method calls the garbage collector.
     *
     * @access public
     * @return Boolean
     */
    public function _close() {
        $this->_gc(100);
        return true;
    }

    /**
     * Is called to read data from a session.
     *
     * @access public
     * @access Integer $id The id of the current session
     * @return Mixed
     */
    public function _read($id) {
        // Create a query to get the session data, ...
        $select = "SELECT
                *
            FROM
                `sessions`
            WHERE
                `sessions`.`id` = :id
            LIMIT 1;";

		    // ... prepare the statement, ...
		    $selectStmt = $pdo->prepare($select);

		    // ... bind the id parameter to the statement ...
		    $selectStmt->bindParam(':id', $id, PDO::PARAM_INT);

		    // ... and try to execute the query.
		    if($selectStmt->execute()) {
			    // Fetch the result as associative array ...
			    $result = $selectStmt->fetch(PDO::FETCH_ASSOC);

			    // ... and validate it.
			    if( !$result ) {
				    throw new Exception("MySqlSession: MySQL error while performing query.");
			    }

			    return $result["value"];
        }

        return '';
    }

    /**
     * Writes data into a session rather
     * into the session record in the database.
     *
     * @access public
     * @access Integer $id The id of the current session
     * @access String $sess_data The data of the session
     * @return Boolean
     */
    public function _write($id, $sess_data) {
        // Validate the given data.
        if( $sess_data == null ) {
            return true;
        }

        // Setup the query to update a session, ...
        $update = "UPDATE
                `sessions`
            SET
                `sessions`.`last_updated` = :time,
                `sessions`.`value` = :data
            WHERE
                `sessions`.`id` = :id;";

		// ... prepare the statement, ...
		$updateStmt = $pdo->prepare($update);

		// ... bind the parameters to the statement ...
		$updateStmt->bindParam(':time', time(), PDO::PARAM_INT);
		$updateStmt->bindParam(':data', $sess_data, PDO::PARAM_STR);
		$updateStmt->bindParam(':id', $id, PDO::PARAM_INT);

		// ... and try to execute the query.
		if($updateStmt->execute()) {
			// Check if any data set was updated.
			if($updateStmt->rowCount() > 0) {
				return true;
			} else {
				// The session does not exists create a new one, ...
				$insert = "INSERT INTO
						`sessions`
						(id, last_updated, start, value)
					VALUES
						(:id, :time, :time, :data);";

				// ... prepare the statement, ...
				$insertStmt = $pdo->prepare($insert);

				// ... bind the parameters to the statement ...
				$insertStmt->bindParam(':time', time(), PDO::PARAM_INT);
				$insertStmt->bindParam(':data', $sess_data, PDO::PARAM_STR);
				$insertStmt->bindParam(':id', $id, PDO::PARAM_INT);

				// .. and finally execute it.
				return $insertStmt->execute();
			}
		}

		return false;
    }

    /**
     * Ends a session and deletes it.
     *
     * @access public
     * @access Integer $id The id of the current session
     * @return Boolean
     */
    public function _destroy($id) {
        // Setup a query to delete the current session, ...
        $delete = "DELETE FROM
                `sessions`
            WHERE
                `sessions`.`id` = '" . $id . "';";

		// ... prepare the statement, ...
		$deleteStmt = $pdo->prepare($delete);

		// ... bind the parameters to the statement ...
		$deleteStmt->bindParam(':id', $id, PDO::PARAM_INT);

		// ... and execute the query.
		return $deleteStmt->execute();
    }

    /**
     * The garbage collector deletes all sessions from the database
     * that where not deleted by the session_destroy function.
     * so your session table will stay clean.
     *
     * @access public
     * @access Integer $maxlifetime The maximum session lifetime
     * @return Boolean
     */
    public function _gc($maxlifetime) {
        // Set a period after that a session pass off.
        $maxlifetime = strtotime("-20 minutes");

        // Setup a query to delete discontinued sessions, ...
        $delete = "DELETE FROM
                `sessions`
            WHERE
                `sessions`.`last_updated` < :maxlifetime;";

		// ... prepare the statement, ...
		$deleteStmt = $pdo->prepare($delete);

		// ... bind the parameters to the statement ...
		$deleteStmt->bindParam(':maxlifetime', $maxlifetime, PDO::PARAM_INT);

		// ... and execute the query.
		return $deleteStmt->execute();
    }
}
?>

<?php
	// Get an instance of the Registry ...
	$reg = Registry::getInstance();

	// ... and fetch a database object.
	$pdo = $reg->get('pdo');

	// Instance SessionHandler, ...
	new MySqlSession($pdo);

	// ... assign some values to the session, ...
	$_SESSION['name'] = 'bornageek';
	$_SESSION['mail'] = 'test@bornageek.com';

	// ... get some session values ...
	print 'Logged in as ' . $_SESSION['name'];

	// ... and destroy the session.
	session_destroy();
?>