def add_product(self, cr, uid, order_id, product_id, qty, context=None):

        """Create a new order line the order"""

        line_obj = self.pool.get('pos.order.line')
        values = self.read(cr, uid, order_id, ['partner_id', 'pricelist_id'])

        pricelist = values['pricelist_id'] and values['pricelist_id'][0]
        product = values['partner_id'] and values['partner_id'][0]

        price = line_obj.price_by_product(cr, uid, [],
                pricelist, product_id, qty, product)

        order_line_id = line_obj.create(cr, uid, {
            'order_id': order_id,
            'product_id': product_id,
            'qty': qty,
            'price_unit': price,
        })
        wf_service = netsvc.LocalService("workflow")
        wf_service.trg_write(uid, 'pos.order', order_id, cr)

        return order_line_id, price