How to store an object in a cookie?

Question

While this is possible in C#: (User is a L2S class in this instance)

User user = // function to get user
Session[\"User\"] = user;

why this

Answer 1

to store an object in a cookie we have to convert it into stringified presentation (compressed or not) which is limited to 4kb. this example demonstrates how to keep a little "Buy" object in a cookies (save/prolong/reset/clear). instead of separate code lines i've used a Json to fill this object with some data.

using System;
using System.Collections.Generic;
using System.Web;
using Newtonsoft.Json;
public class Customer
{
    public int id;
    public string name;
}
public class Order
{
    public int id;
    public decimal total;
    public Customer customer;
}
public class OrderItem
{
    public int id;
    public string name;
    public decimal price;
}
public class Buy
{
    public Order order;
    public List cart;
}
static readonly string cookieName = @"buy";
protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    if (!IsPostBack)
        Restore_Click(null, null);
}
protected void Save_Click(object sender, EventArgs e)
{
    string buy = JsonConvert.SerializeObject(new
    {
        order = new
        {
            id = 1,
            total = 20.10,
            customer = new
            {
                id = 1,
                name = "Stackoverflow"
            }
        },
        cart = new[] {
            new {
                id = 1 , 
                name = "Stack",
                price = 10.05 
            },
            new {
                id = 2 , 
                name = "Overflow",
                price = 10.05 
            }
        }
    });
    HttpContext.Current.Response.Cookies.Add(
        new HttpCookie(cookieName, buy) {
            Expires = DateTime.Now.AddDays(7)
        }
    );
    StatusLabel.Text = "Saved";
}
protected void Prolong_Click(object sender, EventArgs e)
{
    HttpCookie cookie = HttpContext.Current.Request.Cookies[cookieName];
    if (cookie != null)
    {
        cookie.Expires = DateTime.Now.AddDays(7);
        HttpContext.Current.Response.Cookies.Add(cookie);
        StatusLabel.Text = "Prolonged";
    }
    else StatusLabel.Text = "Not prolonged - expired";
}
protected void Restore_Click(object sender, EventArgs e)
{
    Buy buy = null;
    HttpCookie cookie = HttpContext.Current.Request.Cookies[cookieName];
    if (cookie != null)
    {
        buy = JsonConvert.DeserializeObject(cookie.Value);
        StatusLabel.Text = "Restored";
    }
    else StatusLabel.Text = "Not restored - expired";
}
protected void ClearOut_Click(object sender, EventArgs e)
{
    HttpCookie cookie = HttpContext.Current.Request.Cookies[cookieName];
    if (cookie != null)
    {
        cookie.Expires = DateTime.Now.AddMonths(-1);
        HttpContext.Current.Response.Cookies.Add(cookie);
        StatusLabel.Text = "Cleared out";
    }
    else StatusLabel.Text = "Not found - expired";
}