I am still quite new to Codeigniter and have a noob problem I need some help with.

I am trying to set the auto incremented id number for each user to the session data as user_id. eg:

Controller:

$username = $this->input->post('username');
$this->load->model('membership_model');
$user_id = $this->membership_model->getUser_id(); 

$data = array(
    'session_id' => $str = do_hash($str),
    'user_id' => $user_id,
    'username' => $username,
    'is_logged_in' => true
);          
$this->session->set_userdata($data);
redirect('site/members_area');

Model:

public function getUser_id()
{

    $session_username = $this->session->userdata('username');
    
    $q = $this->db->get_where('membership', array('username' => $session_username), 1);
    
    if ($q->num_rows() > 0) {
        foreach ($q->result() as $row) {
            $row->id;
            $row->username;
        }
        return $data;
    }
}

My problem is I am not sure how to pass the $row->id; object from the model to the controller to be used as the user_id.

Can someone please provide some advice or am I approaching this in the wrong way?