ASP.NET MVC: Best practices for keeping session state in a wizard-like app

Question

Let's say I have a Web application implemented like a set of wizard pages to edit a complex object. Until the user clicks on the "Finish" button, the object doesn't get saved to the back-end system (a requirement), so in the meantime I have to keep the whole information about the object in some kind of a session state.

Also, some of the wizard pages have to show combo and list boxes with potentially large number of items. These items are fetched from the back-end system using a Web service.

Coincidentally, the wizard allows the user to freely jump from one wizard page to any other (using tab links on top of the form), so it's not a simple "next, next... finish" thing.

Additional constraint: the Web application runs on a Web farm and the customer is weary of using server-side session state. In the best case they want to keep the size of the session state minimal (they had problems with this in the past).

So basically there are two problems here:

1. How/where to keep data entered by the user in the Wizard?
2. Whether to cache the combo/list items received from the back-end and if so, where?

Options I'm considering:

1. Storing the object in a WebForms-like ViewState (by serializing it into the HTML page). This would also include the combo box items. Obviously, there could be a problem with HTML pages becoming very large and thus Web application will be slow.

2. Storing it into server-side session state, regardless of the customer's wishes and without knowing how the performance will be affected until it is tested on the actual Web farm (late in the project).

I cannot decide between the two. Or is there another alternative?

Answer 1

Why cache at all? You could just have the tabbed pages where each page is a div or panel and just display the current div relating to your tab. That way you dont have to keep track and process all the inputs when the user submits the form.

Answer 2

As Daisy said, it doesn't have to be cached. You could also use hidden form fields. Because these could map to the same object on each controller action, you could progressively build the object through successive pages.

//Here's a class we're going to use
public class Person
{
  public int Age {get;set;}
  public string Name {get;set;}

  public Person()
  {
  }
}

//Here's the controller
public Controller PersonCreator
{
  public ActionResult CreatePerson()
  {
    //Posting from this page will go to SetPersonAge, as the name will be set in here.
    return View();
  }

  public ActionResult SetPersonAge(Person person)
  {
    //This should now have the name and age of the person
    return View(person);
  }
}

//Here is your SetPersonAge, which contains the name in the model already:
<%= Html.Hidden("Name", Model.Name) %>
<%Html.TextBox("Age") %>

And that's pretty much it.

Answer 3

Is it possible to store the wizard data in a temporary table in the database? When the user finishes the wizard the data is copied from the temporary table and deleted. The temporary table includes a timestamp to remove any old uncompleted data.

Answer 4

I can suggest a few more options

1. Having the entire wizard as a single page with the tabs showing and hiding content via javascript on the client-side. This may cause the the initial page to load slower though.

2. Caching the data at the server using the caching application block (or something similar). This will allow all the users to share a single instance of this data instead of duplicating across all sessions. Now that the data is lighter, you may be able to convince the customer to permit storing in the session.

Answer 5

I've been dealing with the same issue and, while my requirements are a little simpler (keeping state for just a few strings), my solution may work for you. I'd also be interested in hearing others thoughts on this approach.

What I ended up doing is: in the controller I just dump the data I want into the Session property of the Controller and then pull it out next time I need it. Something like this for your situation:

//Here's the controller
public Controller PersonCreator  
{  
    public ActionResult CreatePerson()  
    {    
        //get the age out of the session
        int age = (int)(Session["age"]);
        //do something with it...
        return View();  
    }  
    public ActionResult SetPersonAge(Person person)  
    {  
        //put the age in the session
        Session.Add("age", person.Age);
        return View(person);  
    }
}

The thing I like about this is I don't have to put a bunch of hidden params around on my view pages.