Question

Here’s the one I’m using:

<?php
final class Database {
    private static $oDb;
    public static function init() {
        if(self::$oDb == NULL)
        {
            self::$oDb = mysql_connect('localhost', 'mysql_user', 'mysql_password') or die(mysql_error());
            mysql_select_db('mysql_db_name', self::$oDb) or die (mysql_error());;
        }
        return self::$oDb;
    }
    public function query($sql)
    {
        return mysql_query($sql) or die(mysql_error());
    }
}
?>

Usage:

$oDb = Database::init();
$sql = foo;
$oDb->query($sql);

Assuming that I only want it to connect and execute this one query function, are there any improvements I should make on the class? Memory or efficiency of code?

Also, is there an efficient way I can get the db credentials from a config file? I know I can’t use includes inside my class.

Answer 1

I usually use lazy initialization for this sort of situation and only have one public method (in this case), with a private constructor to prevent outside instantiation (per the Singleton pattern):

class Database {
  private static $instance;
  private $conn;

  private function Database() {
    // do init stuff
    require_once('dbconfig.php'); // contains define('DB_USER', 'webuser'); etc...
    $this->conn = mysql_connect(DB_HOST, DB_USER, DB_PASS); // do error checking
  }

  public static function getInstance() {
    if(!self::$instance) {
      self::$instance = new Database();
    }
    return self::$instance;
  }

  public static function query($sql) {
    $instance = self::getInstance();
    return mysql_query($sql, $instance->conn);
  }
}

Then you can just call $dbHandle = Database::getInstance() anytime you need to use it. Or in this case since a static query method is defined, you can use Database::query("select * from xx;"); without having to call any sort of init at all.