[codeigniter] using multiple database

DB_Controller.php

<?php
/***
 * filepath: application/core/MY_Controller.php
 */

//setup your base controller
class DB_Controller extends CI_Controller {

    //declare them globally in your controller
    protected $billing_db;
    protected $inventory_db;

    function __construct() 
    {
        parent::__construct();

        //Load them in the constructor
        $this->billing_db = $this->load->database('billing', TRUE);
        $this->inventory_db = $this->load->database('inventory', TRUE);
    }

}

example.php

<?php
/***
 * filepath: application/controllers/example.php
 */

//Extend the Base Controller
class Example extends DB_Controller {

    function __construct()
    {
        parent::__construct();
    }

    function index()
    }
        //Then use them in any controller like this
        $data['billing'] = $this->inventory_db->get('stuff');
        $data['inventory'] = $this->billing_db->get('stuff');
    }

}