MVC Global variables reseting to null when entering another action method

Question

public class MusicController : Controller
{
    User currentUser;

    public PartialViewResult UploadMusic()
    {

        return PartialView("_UploadMusic");
    }

    [HttpPost]
    public ActionResult UploadMusic(List<HttpPostedFileBase> files)
    {
        EntityDBContext db = new EntityDBContext();
        List<Song> uploadedSongs = new List<Song>();

        foreach (var file in files)
        {
            if (file != null)
            {
                string songName = Path.GetFileName(file.FileName);
                byte[] songAsBytes = new byte[file.ContentLength];

                using (BinaryReader br = new BinaryReader(file.InputStream))
                {
                    songAsBytes = br.ReadBytes(file.ContentLength);
                }

                //Save new record in database
                Song song = new Song
                {
                    SongName = songName,
                    SongBytes = songAsBytes
                };

                uploadedSongs.Add(song);
            }
        }

        string userName = User.Identity.Name;
        currentUser = db.Users.Where(x => x.Username == userName).First();
        currentUser.UserSongs = uploadedSongs;

        return ShowSongs(currentUser.UserSongs);
    }

    public ActionResult ShowSongs(List<Song> UserSongs)
    {
        return View("ShowSongs", UserSongs);
    }

    public ActionResult Publish()
    {
        EntityDBContext db = new EntityDBContext();

        foreach (var song in currentUser.UserSongs)
        {
            if (song != null)
            {
                db.Songs.Add(song);
                db.SaveChanges();
            }
        }
        return View();
    }
}

ShowSongs view:

@model List<Vidafo.Models.Song>

@Html.ActionLink("Publish", "Publish")

The Problem

So I declare currentUser at the top of the controller. I then assign a value to that with this line here currentUser.UserSongs = uploadedSongs; This works fine but when the code goes into Publish() currentUser.UserSongs is null.

I need to have access to currentUser.UserSongs in more than one action method after assigning a value but it seems that it resets to null when it enters another action.

Answer 1

Object state isn't maintained across requests, that's not how web applications work. Every time a request is sent to the server, a new instance of the controller object is created. So any instance-level values are new.

In order to persist information across requests you need to persist it somewhere. For something like a user context, session state is a common choice. You'll probably want to wrap it in a common provider interface so as to not couple your controllers to an HTTP context, but at its core storing in session is simple:

HttpContext.Current.Session["someKey"] = someValue;

(You could even re-fetch from the database with each request. It's slightly less performant, but very simple and robust.)

Don't count out the ASP.NET identity system for this, though. ASP.NET is pretty good at abstracting a lot of this for you. You're already using it here:

string userName = User.Identity.Name;

Then you use that value to get the user from the database. You could extend the identity system to store a custom user object which fits your needs. But that's a larger scope effort outside of this question.