Where should I store functions like...?

[eluser]Carmichael[/eluser]
Hi CodeIgniters!

Where should I store functions like this

Code:

function get_username_by_id($id)
    {
        $q = $this->db->select('user_name')->get_where($this->users_table, array('user_id' => $id));
        
        if (!empty($q->row(0)->user_name))
        {
            return $q->row(0)->user_name;
        } else{
            return false;
        }
    }

I use that kind of functions in multiple controllers/views, so should I store that kind of functions in a helper or what?

I think it is more convenient to make such functions than to build big querys with joins.