set relation with two tables

Sorry I not speak English that is google traslator ;) I hope you can understand me

i have that

public function orders() {
        try {
            /* This is only for the autocompletion */
            $crud = new grocery_CRUD();
            $crud->set_table('orders');

            $crud->set_relation('customer_id', 'customer', 'name');

            $output = $crud->render();
            $this->_main_output($output);
        } catch (Exception $e) {
            show_error($e->getMessage() . ' --- ' . $e->getTraceAsString());
        }
    }

I need to create the orders but only to customers who have a contract and that the date not expired

Thanks

yoandry