Something wrong in my model

I answer myself I've found the way here is my corrected model function find() :  

PHP Code:

public function find($value) {

        $this->load->database();
        $q = $this->db->get_where("stages", array("id_stages" => $value), 1);
        $r = $q->result(get_class($this))[0];
        $r->set_sessions(); // a private method to complete this object

        return $r;
    } 


Now it works perfectly ! 

I hope this could help

see you next time, I really enjoy CI my next project will use CI 3