CodeIgniter using Zend Library

Zend_Db.php

Structure:

applications/libraries/Zend
- Db/
- Db.php
- Exception.php


applications/core/MY_Controller.php
<?php
class MY_Controller extends CI_Controller
{
    function __construct()
    {
        parent::__construct();
        
        set_include_path(implode(PATH_SEPARATOR, array(
            realpath(APPPATH . 'libraries')
        )));
        require_once 'Zend/Loader.php';

        //Zend Library
        Zend_Loader::loadClass('Zend_Db');
    }
}
?>

applications/config/config.php
<?php
$config['db']['host'] = 'localhost';
$config['db']['dbname'] = 'database';
$config['db']['username'] = 'root';
$config['db']['password'] = '';
?>

applications/core/MY_Model.php
<?php

class MY_Model extends CI_Model {

    protected $_oDb;
    function __construct()
    {
        parent::__construct();

        $aDbConfig = $this->config->item('db');
        $this->_oDb = $db = Zend_Db::factory('Pdo_Mysql', $aDbConfig );
    }
}
?>

applications/models/Auth.php
<?php

class Auth extends MY_Model {

    function doAuth($sUsername, $sPassword)
    {
        $data = $this->_oDb->fetchAll('SELECT * FROM table');
        die(var_export($data,true));
    }
}
?> 

Zend_Loader.php

Structure
applications/libraries/Zend
- Loader/
- Loader.php
- Json/
- Json.php

application/core/MY_Controller.php

class MY_Controller extends CI_Controller
{

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

  set_include_path(implode(PATH_SEPARATOR,array(
   APPPATH.'/libraries',
  )));

  include 'Zend/Loader.php';
 }

}


application/controllers/welcome.php

class Welcome extends MY_Controller {

 public function index()
 {
  $aData = array('content'=>'Hello World!');

  Zend_Loader::loadClass('Zend_Json');
  echo Zend_Json::encode($aData);
 }
}