define('_PS_MODE_DEV_', false);

define('_PS_MODE_DEV_', true);

$this->fields_list['supplier_reference'] = array(
    'title' => $this->l('Supplier reference'),
    'align' => 'left',
    'callback' => 'getSupplierRef',
        );
{
    return Db::getInstance()->getValue('SELECT `product_supplier_reference` FROM `'._DB_PREFIX_.'product_supplier` WHERE `product_supplier_reference` IS NOT NULL AND `product_supplier_reference` != \'\' AND `id_product` = ' . (int)$p['id_product']);
}