multi-step registration process issues in asp.net mvc (split viewmodels, single model)

Question

I have a multi-step registration process, backed by a single object in domain layer, which have validation rules defined on properties.

Answer 1

To supplement on Amit Bagga's answer you will find below what I did. Even if less elegant I find this way simpler than Darin's answer.

Controller :

public ActionResult Step1()
{
    if (Session["wizard"] != null)
    {
        WizardProductViewModel wiz = (WizardProductViewModel)Session["wizard"];
        return View(wiz.Step1);
    }
    return View();
}

[HttpPost]
public ActionResult Step1(Step1ViewModel step1)
{
    if (ModelState.IsValid)
    {
        WizardProductViewModel wiz = new WizardProductViewModel();
        wiz.Step1 = step1;
        //Store the wizard in session
        Session["wizard"] = wiz;
        return RedirectToAction("Step2");
    }
    return View(step1);
}

public ActionResult Step2()
{
    if (Session["wizard"] != null)
    {
        WizardProductViewModel wiz = (WizardProductViewModel)Session["wizard"];
        return View(wiz.Step2);
    }
    return View();
}

[HttpPost]
public ActionResult Step2(Step2ViewModel step2)
{
    if (ModelState.IsValid)
    {
        //Pull the wizard from session
        WizardProductViewModel wiz = (WizardProductViewModel)Session["wizard"];
        wiz.Step2 = step2;
        //Store the wizard in session
        Session["wizard"] = wiz;
        //return View("Step3");
        return RedirectToAction("Step3");
    }
    return View(step2);
}

public ActionResult Step3()
{
    WizardProductViewModel wiz = (WizardProductViewModel)Session["wizard"];
    return View(wiz.Step3);
}

[HttpPost]
public ActionResult Step3(Step3ViewModel step3)
{
    if (ModelState.IsValid)
    {
        //Pull the wizard from session
        WizardProductViewModel wiz = (WizardProductViewModel)Session["wizard"];
        wiz.Step3 = step3;
        //Save the data
        Product product = new Product
        {
            //Binding with view models
            Name = wiz.Step1.Name,
            ListPrice = wiz.Step2.ListPrice,
            DiscontinuedDate = wiz.Step3.DiscontinuedDate
        };

        db.Products.Add(product);
        db.SaveChanges();
        return RedirectToAction("Index", "Product");
    }
    return View(step3);
}

Models :

 [Serializable]
    public class Step1ViewModel 
    {
        [Required]
        [MaxLength(20, ErrorMessage="Longueur max de 20 caractères")]
        public string Name { get; set; }

    }

    [Serializable]
    public class Step2ViewModel
    {
        public Decimal ListPrice { get; set; }

    }

    [Serializable]
    public class Step3ViewModel
    {
        public DateTime? DiscontinuedDate { get; set; }
    }

    [Serializable]
    public class WizardProductViewModel
    {
        public Step1ViewModel Step1  { get; set; }
        public Step2ViewModel Step2  { get; set; }
        public Step3ViewModel Step3  { get; set; }
    }