Saving PHP sessions in a database, using PDO.

index.php

// Index.php
<?php

require_once("connection.php");
require_once("database.class.php");
require_once("session.class.php");
$session = new Session;

if(!isset($_SESSION["counter"])){
	$_SESSION["counter"] = 0;
}

// Increase counter
echo $_SESSION["counter"]++;

?>

// connection.php
<?php

// Define database connection
define("DB_HOST", "localhost");
define("DB_USER", "XXX");
define("DB_PASS", "XXX");
define("DB_NAME", "XXX");

?>

// database.class.php
<?php

class Database {

    private $host      = DB_HOST;
    private $user      = DB_USER;
    private $pass      = DB_PASS;
    private $dbname    = DB_NAME;

    private $dbh;
    private $error;

    private $stmt;

    public function __construct() {

        // Set DSN
        $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
        // Set options
        $options = array(
            PDO::ATTR_PERSISTENT    => true,
            PDO::ATTR_ERRMODE       => PDO::ERRMODE_EXCEPTION
        );
        // Create a new PDO instanace
        try {
            $this->dbh = new PDO($dsn, $this->user, $this->pass, $options);
        } catch(PDOException $e){ // Catch any errors
            $this->error = $e->getMessage();
        }
    }

	public function query($query) {

	    $this->stmt = $this->dbh->prepare($query);

	}

	public function bind($param, $value, $type = null) {

	    if (is_null($type)) {
	        switch (true) {
	            case is_int($value):
	                $type = PDO::PARAM_INT;
	                break;
	            case is_bool($value):
	                $type = PDO::PARAM_BOOL;
	                break;
	            case is_null($value):
	                $type = PDO::PARAM_NULL;
	                break;
	            default:
	                $type = PDO::PARAM_STR;
	        }
	    }

	    $this->stmt->bindValue($param, $value, $type);
	}


	public function execute() {

	    return $this->stmt->execute();
	}


	public function resultset() {

	    $this->execute();
	    return $this->stmt->fetchAll(PDO::FETCH_ASSOC);

	}

	public function single() {

	    $this->execute();
	    return $this->stmt->fetch(PDO::FETCH_ASSOC);

	}

	public function rowCount() {

	    return $this->stmt->rowCount();

	}

	public function fetchColumn() {

		$this->execute();
	    return $this->stmt->fetchColumn();

	}

	public function lastInsertId() {
	    return $this->dbh->lastInsertId();

	}

} // End class

?>

// session.class.php
<?php

class Session {

	public function _construct(){
	  // Instantiate new Database object
	  $this->db = new Database;

	  // Set handler to overide SESSION
	  session_set_save_handler(
	    array($this, "_open"),
	    array($this, "_close"),
	    array($this, "_read"),
	    array($this, "_write"),
	    array($this, "_destroy"),
	    array($this, "_gc")
	  );

	  // Start the session
	  session_start();
	}

/**
 * Open
 */
public function _open(){
  // If successful
	if($this->db){
    // Return True
    return true;
  }
  return false;
}

/**
 * Close
 */
public function _close(){
  // Close the database connection
  // If successful
	if($this->db->close()){
    // Return True
    return true;
  }
  return false;
}


/**
 * Read
 */
public function _read($id){
  // Set query
	$this->db->query('SELECT data FROM sessions WHERE id = :id');

  // Bind the Id
	$this->db->bind(':id', $id);

  // Attempt execution
  // If successful
	if($this->db->execute()){
    // Save returned row
    $row = $this->db->single();
    // Return the data
    return $row['data'];
  }else{
    // Return an empty string
    return '';
  }
}

/**
 * Write
 */
public function _write($id, $data){
  // Create time stamp
  $access = time();

  // Set query
	$this->db->query('REPLACE INTO sessions VALUES (:id, :access, :data)');

  // Bind data
	$this->db->bind(':id', $id);
	$this->db->bind(':access', $access);
	$this->db->bind(':data', $data);

  // Attempt Execution
  // If successful
	if($this->db->execute()){
    // Return True
    return true;
  }

  return false;
}

/**
 * Destroy
 */
public function _destroy($id){
  // Set query
	$this->db->query('DELETE FROM sessions WHERE id = :id');

  // Bind data
	$this->db->bind(':id', $id);

  // Attempt execution
  // If successful
	if($this->db->execute()){
    // Return True
    return true;
  }

  return false;
}


/**
 * Garbage Collection
 */
public function _gc($max){
  // Calculate what is to be deemed old
  $old = time() - $max;

  // Set query
	$this->db->query('DELETE * FROM sessions WHERE access < :old');

  // Bind data
	$this->db->bind(':old', $old);

  // Attempt execution
	if($this->db->execute()){
    // Return True
    return true;
  }

  return false;
	}

}

?>