How do I maintain ModelState errors when using RedirectToAction?

Question

I have some code that saves a ticket in our system. If there is an error it does a RedirectToAction. The problem is that I don\'t seem to have my errors in the new action.

Answer 1

Use the TempData[] Collection

The tempdata is stored from one request to the next, then its gone.

Answer 2

The PRG pattern is ok, but I did this:

Base controller:

protected override void OnActionExecuted(ActionExecutedContext filterContext)
{
    if (TempData["ModelState"] != null && !ModelState.Equals(TempData["ModelState"]))
        ModelState.Merge((ModelStateDictionary)TempData["ModelState"]);

    base.OnActionExecuted(filterContext);
}

Action (I'm using xVal):

try
{
    user.Login();
    AuthenticationManager.SignIn(user);
}
catch (RulesException rex)
{
    // on bad login
    rex.AddModelStateErrors(ModelState, "user");
    TempData["ModelState"] = ModelState;
    return Redirect(Request.UrlReferrer.ToString());
}

The action throws an exception, adds the ModelState to TempData and redirects back to the referrer. Since the action is caught, OnActionExecuted is still executed, but the first time around the ModelState is the same as TempData["ModelState"], so you don't want to merge with yourself. When the redirect action is executed, OnActionExecuted fires again. This time, if there's anything in TempData["ModelState"], it merges with this action's ModelState.

You could expand it to multiple models by using TempData["ModelState.user"] = ModelState and then merging every TempData object that starts with ModelState.

Answer 3

I know this thread is old, but this blog about ASP.NET Best Practices has some excellent suggestions.
#13 on the page deals with using 2 Action filters to save and restore ModelState between redirects.

This is the pattern that my work uses, and I love it.

Here's the simplified example:

[ImportModelStateFromTempData]
public ActionResult Dashboard()
{
    return View();
}

[AcceptVerbs(HttpVerbs.Post), ExportModelStateToTempData]
public ActionResult Dashboard(string data)
{
    if (ValidateData(data))
    {
        try
        {
            _service.Submit(data);
        }
        catch (Exception e)
        {
            ModelState.AddModelError(ModelStateException, e);
        }
    }

    return RedirectToAction("Dashboard");
}

Answer 4

What I did to maintain my ModelState no matter where I go with redirects is the following:

1. In your model, add:

   public ModelStateDictionary modelstate { get; set; }
   

2. In your model's constructor, add:

   this.modelstate = new System.Web.Mvc.ModelStateDictionary();
   

3. Sample Post with my model called Models.ContactInformation:

   [HttpPost]
   [ValidateAntiForgeryToken]
   public ActionResult contact(Models.ContactInformation con)
   {
     if (string.IsNullOrEmpty(con.SelectedAgencySelectorType))
     {
       ModelState.AddModelError("", "You did not select an agency type.");
     }
   
     con.modelstate = ModelState;
     TempData["contact"] = con;
     if (!ModelState.IsValid) return RedirectToAction("contactinformation", "reports");
   
       //do stuff
   
       return RedirectToAction("contactinformation", "reports");
   }
   

4. So now your tempdata has your model and modelstate as is.

5. The following is my view that is agnostic to the state of anything, unless it has something. Here's the code:

   [HttpGet]
   public ActionResult contactinformation()
   {
       //try cast to model
       var m = new Models.ContactInformation();
       if (TempData["contact"] is Models.ContactInformation) m = (Models.ContactInformation)TempData["contact"];
   
       //restore modelstate if needed
       if (!m.modelstate.IsValid)
       {
           foreach (ModelState item in m.modelstate.Values)
           {
               foreach (ModelError err in item.Errors)
               {
                   ModelState.AddModelError("", err.ErrorMessage.ToString());
               }
           }
       }
   
       return View(m);
   }
   

Answer 5

this blog post describes how you could implement the PRG-Pattern in MVC http://blog.simonlovely.com/archive/2008/11/26/post-redirect-get-pattern-in-mvc.aspx

hth