Question

Once a user has logged in- I want all my models to know the user’s id. (Even if they are called later on).

I thought about using a static variable but it doesn’t seem to work

class Base_model extends CI_Model {
    static protected $user_id;
}

class Log_in_model extends Base_model {
    public function log_in(){
        self::$user_id = 69;
    }
}

class A_model extends Base_model {
    public function do_A(){
        echo self::$user_id;
    }
}

class B_model extends Base_model {
    public function do_B(){
        echo self::$user_id;
    }
}

Answer 1

initailize session

$this->load->library('session');

after user logs in,save the userdata in session userdata

$newdata = array(
               'username'  => 'USERNAME',
               'email'     => 'EMAIL',
               'user_id'   => 'USERID',
               'logged_in' => TRUE
           );

$this->session->set_userdata('userdetails',$newdata);   //setting data in session with a name userdetails 

get the session userdata..

 print_r($this->session->userdata('userdetails'));  //get userdetails from session

to destroy userdetails from session use..

$this->session->unset_userdata('userdetails'); 

if u want to read more about session then read this..

http://ellislab.com/codeigniter/user-guide/libraries/sessions.html