php - Call to a member function where() on a non-object -

i'm developing website using codeigniter. when open page error :

i haven't encountered problem before, , know have in every controller uses database library.

this example of function in model error :

 public function login($pseudo,$password)   {      $this->db->where("pseudo",$pseudo);     $this->db->where("password",$password);      $query=$this->db->get("admin");     if($query->num_rows()>0)     {       foreach($query->result() $rows)       {         //add data session         $newdata = array(           'admin_id'  => $rows->id,           'admin_pseudo'    => $rows->pseudo,           'admin_fullname' => $rows->fullname,           'admin_email' => $rows->email,           'admin_logged_in'  => true,         );       }       $this->session->set_userdata($newdata);       return true;     }     return false;   } 

the line 13 : $this->db->where("pseudo",$pseudo);

this controller :

public function login()   {     $this->load->library('form_validation');     $this->form_validation->set_rules('login', 'pseudo', 'trim|required|min_length[4]|max_length[32]');     $this->form_validation->set_rules('password', 'password', 'trim|required|min_length[4]|max_length[32]');     $pseudo=$this->input->post('login');      $password=md5($this->input->post('password'));       $result=$this->admin_model->login($pseudo,$password);        if($this->form_validation->run() == false)     {       $this->index();     }     else     {       if ($result) $this->dashboard();       else                 $this->index();     }   } 

in autoload file have :

$autoload['libraries'] = array('database','session'); 

$this->db not object apparently. check it's initialized before calling login()