void ProductDetails::add_to_cart(HttpServletRequest& request, HttpServletResponse &response) {
HttpSession* session = request.getSession(false);
if(!session) throw runtime_error("no session");
typedef vector<cart_item> shopping_cart;
shopping_cart cart = session->getAttribute<shopping_cart>("cart");
cart_item item;
item.quantity = boost::lexical_cast<int>(request.getParameter("quantity"));
item.product = fetch(request.getParameter("product_id"));
if(item.quantity <= 0)
throw runtime_error("Quantity is invalid. It must be a positive number");
cart.push_back(item);
session->setAttribute("cart",cart);
response.sendRedirect("ShoppingCart.sxx");
}
