tidak bisa ganti Tabel

class Loginpanitia extends Controller {
 
function index() {
   $isi['header']='header';
   $isi['isi'] = 'loginPanitia';
   $isi['kiri']= 'kiri';
   $this->load->view('template', $isi);
}
 
function validate_login() {
	$this->load->model('panitialist');
	$query = $this->panitialist->validasi();
 
	if ($query) 
 
 
	{
		$session = array(
		'username'=> $this->input->post('username'),
		'is_logged_in'=>true
		);
		$this->session->set_userdata($session);
		redirect('site/Panitia');
	}
	else
	{
	 $this->index();
	}	
  }
 
}

class Panitialist extends Model {
 
	function validasi()
	{
	$this->db->where('username', $this->input->post('username'));
	$this->db->where('password', md5($this->input->post('password')));
 
	$ambil = $this->db->get('admin');
 
	 if($ambil->num_rows == 1) 
	 {
	   return true;
	 }
	}
 
}