Codeigneter : How to call model method from controller class?

Question

I've recently started to learn OOP and Codeigniter. I've set up 2 new files in core; MY_Controller.php extending CI_Controller and MY_Model.php extending CI_Model. These files are both working, i'm able to call their methods in various controllers and models. However, I have a method in MY_Controller that checks if a user's logged in, if so it calls a method from MY_Model that updates the last active field in the user table. This method is working when I call it from say Login_model, but when I call it from MY_Controller it passes an error:

Call to undefined method Feed::update_last_active()

Why is this? I'm trying to call a core model from my core controller, should I not be doing this? Below is my code.

MY_Controller.php:

class MY_Controller extends CI_Controller{

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

    /**
    *   Check if the users sessions logged in
    */
    public function logged_in(){

        //Check the flag logged_in exists in the session
        if ($this->session->userdata('logged_in')){
            //Update the last active field in the user db
            $this->update_last_active($this->session->userdata('user_id'));
            return true;
        } else {
            return false;
        }

    }

}

MY_Model.php:

class MY_Model extends CI_Model{

    /**
    *   Updates users last active 
    */
    public function update_last_active($id){

        $this->db->where('id', $id);
        $this->db->update('users', array('last_active' => date('Y-m-d H:i:s')));

    }

}

MY_Controller updated to @Tiger response (Returns Call to undefined method CI_Loader::update_last_active() ):

public function logged_in(){

        //Check the flag logged_in exists in the session
        if ($this->session->userdata('logged_in')){

            //Load my model
            $my_model = $this->load->model('MY_Model');

            //Update the last active field in the user db
            $my_model->update_last_active($this->session->userdata('user_id'));
            return true;
        } else {
            return false;
        }

    }

Answer 1

You didn't load the model in the controller, load the model in my_controller

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

         //load the model  
         $this->load->model('My_Model');  

    }

This should solve the issue. logged_in function too have some errors, try loading the model in the _construct() first

Answer 2

Controller file:

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

         $this->load->model('My_Model'); //Load the Model here   

 }

 public function logged_in(){

        if ($this->session->userdata('logged_in')){

            //Now Load Only Model Method        
            $my_model = $this->MY_Model->update_last_active();
            $my_model->update_last_active($this->session->userdata('user_id'));
            return true;
        } else {
            return false;
        }

    }