Login gagal (Codeigniter)

permisi saya sedang mencoba untuk membuat login dengan menggunakan CI, tapi kenapa tak bisa login yaa? apakah code ini masih ada yg salah? mohon pencerahan nya

controller

 <?php if (!defined('BASEPATH')) exit('No direct script access allowed');

class Auth extends CI_Controller {

    public function index($error = NULL) {
        $data = array(
            'title' => 'Login Page',
            'action' => site_url('dashboard'),
            'error' => $error
        );
        $this->load->view('login', $data);
    }

    public function login() {
        $this->load->model('auth_model');
        $login = $this->auth_model->login($this->input->post('username'), md5($this->input->post('password')));

        if ($login == 1) {

            $row = $this->auth_model->data_login($this->input->post('username'), md5($this->input->post('password')));


            $data = array(
                'logged' => TRUE,
                'username' => $row->username
            );
            $this->session->set_userdata($data);


            redirect(site_url('dashboard'));
        } else {

            $error = 'username / password salah';
            $this->index($error);
        }
    }

    function logout() {

        $this->session->sess_destroy();


        redirect(site_url('login'));
    }

}

model

 <?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Auth_model extends CI_Model {

//    untuk mengcek jumlah username dan password yang sesuai
    function login($username,$password) {
        $this->db->where('username', $username);
        $this->db->where('password', $password);
        $query =  $this->db->get('apart');
        return $query->num_rows();
    }

//    untuk mengambil data hasil login
    function data_login($username,$password) {
        $this->db->where('username', $username);
        $this->db->where('password', $password);
        return $this->db->get('apart')->row();
    }
}