<?php

class DB {

    const DB_USER = 'root';
    const DB_PASS = 'password';
    const DB_HOST = 'localhost';

    protected static $dbh_hash = array();

    public static function Get ($db_name) {
        if(isset(self::$dbh_hash[$db_name])) {
            return self::$dbh_hash[$db_name];
        } else {
            try {
                // Open the database
                $pdo = new PDO
                (
                // If host is localhost, leave out and connect via socket
                'mysql:' . (self::DB_HOST == 'localhost' ? '' : 'host=' . self::DB_HOST . ';') . 'dbname=' . $db_name . ';',
                self::DB_USER,
                self::DB_PASS
                );

                // Put PDO into exception error mode
                $pdo->setAttribute (PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

                // Allow buffered queries in  MySQL
                $pdo->setAttribute (PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
            } catch (PDOException $Ex) {
                throw new Exception ('Could not connect to database');
            }
            $dbh_hash[$db_name] = $pdo;
            return $pdo;
        }
    }
}

$db = DB::Get('database_name');

?>