ASP.NET MVC - How to Preserve ModelState Errors Ac

Question

I have the following two action methods (simplified for question):

[HttpGet]
public ActionResult Create(string uniqueUri)
{
   // get some stuff based on uniqueuri, set in ViewData.  
   return View();
}

[HttpPost]
public ActionResult Create(Review review)
{
   // validate review
   if (validatedOk)
   {
      return RedirectToAction("Details", new { postId = review.PostId});
   }  
   else
   {
      ModelState.AddModelError("ReviewErrors", "some error occured");
      return RedirectToAction("Create", new { uniqueUri = Request.RequestContext.RouteData.Values["uniqueUri"]});
   }   
}

So, if the validation passes, i redirect to another page (confirmation).

If an error occurs, i need to display the same page with the error.

If i do return View(), the error is displayed, but if i do return RedirectToAction (as above), it loses the Model errors.

I'm not surprised by the issue, just wondering how you guys handle this?

I could of course just return the same View instead of the redirect, but i have logic in the "Create" method which populates the view data, which i'd have to duplicate.

Any suggestions?

Answer 1

I have a method that adds model state to temp data. I then have a method in my base controller that checks temp data for any errors. If it has them, it adds them back to ModelState.

Answer 2

You need to have the same instance of Review on your HttpGet action. To do that you should save an object Review review in temp variable on your HttpPost action and then restore it on HttpGet action.

[HttpGet]
public ActionResult Create(string uniqueUri)
{
   //Restore
   Review review = TempData["Review"] as Review;            

   // get some stuff based on uniqueuri, set in ViewData.  
   return View(review);
}
[HttpPost]
public ActionResult Create(Review review)
{
   //Save you object
   TempData["Review"] = review;

   // validate review
   if (validatedOk)
   {
      return RedirectToAction("Details", new { postId = review.PostId});
   }  
   else
   {
      ModelState.AddModelError("ReviewErrors", "some error occured");
      return RedirectToAction("Create", new { uniqueUri = Request.RequestContext.RouteData.Values["uniqueUri"]});
   }   
}

Also i would advice, if you want to make it work also when browser refresh button pressed after HttpGet action executed first time, you may go like that

  Review review = TempData["Review"] as Review;  
  TempData["Review"] = review;

Otherwise on refresh button object review will be empty because there wouldn't be any data in TempData["Review"].

Answer 3

Why not create a private function with the logic in the "Create" method and calling this method from both the Get and the Post method and just do return View().

Answer 4

My scenario is a little bit more complicated as I am using the PRG pattern so my ViewModel ("SummaryVM") is in TempData, and my Summary screen displays it. There is a small form on this page to POST some info to another Action. The complication has come from a requirement for the user to edit some fields in SummaryVM on this page.

Summary.cshtml has the validation summary which will catch ModelState errors that we'll create.

@Html.ValidationSummary()

My form now needs to POST to a HttpPost action for Summary(). I have another very small ViewModel to represent edited fields, and modelbinding will get these to me.

The new form:

@using (Html.BeginForm("Summary", "MyController", FormMethod.Post))
{
    @Html.Hidden("TelNo") @* // Javascript to update this *@

and the action...

[HttpPost]
public ActionResult Summary(EditedItemsVM vm)

In here I do some validation and I detect some bad input, so I need to return to the Summary page with the errors. For this I use TempData, which will survive a redirection. If there is no issue with the data, I replace the SummaryVM object with a copy (but with the edited fields changed of course) then do a RedirectToAction("NextAction");

// Telephone number wasn't in the right format
List<string> listOfErrors = new List<string>();
listOfErrors.Add("Telephone Number was not in the correct format. Value supplied was: " + vm.TelNo);
TempData["SummaryEditedErrors"] = listOfErrors;
return RedirectToAction("Summary");

The Summary controller action, where all this begins, looks for any errors in the tempdata and adds them to the modelstate.

[HttpGet]
[OutputCache(Duration = 0)]
public ActionResult Summary()
{
    // setup, including retrieval of the viewmodel from TempData...


    // And finally if we are coming back to this after a failed attempt to edit some of the fields on the page,
    // load the errors stored from TempData.
        List<string> editErrors = new List<string>();
        object errData = TempData["SummaryEditedErrors"];
        if (errData != null)
        {
            editErrors = (List<string>)errData;
            foreach(string err in editErrors)
            {
                // ValidationSummary() will see these
                ModelState.AddModelError("", err);
            }
        }

Answer 5

I had to solve this problem today myself, and came across this question.

Some of the answers are useful (using TempData), but don't really answer the question at hand.

The best advice I found was on this blog post:

http://www.jefclaes.be/2012/06/persisting-model-state-when-using-prg.html

Basically, use TempData to save and restore the ModelState object. However, it's a lot cleaner if you abstract this away into attributes.

E.g.

public class SetTempDataModelStateAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        base.OnActionExecuted(filterContext);         
        filterContext.Controller.TempData["ModelState"] = 
           filterContext.Controller.ViewData.ModelState;
    }
}

public class RestoreModelStateFromTempDataAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        base.OnActionExecuting(filterContext);
        if (filterContext.Controller.TempData.ContainsKey("ModelState"))
        {
            filterContext.Controller.ViewData.ModelState.Merge(
                (ModelStateDictionary)filterContext.Controller.TempData["ModelState"]);
        }
    }
}

Then as per your example, you could save / restore the ModelState like so:

[HttpGet]
[RestoreModelStateFromTempData]
public ActionResult Create(string uniqueUri)
{
    // get some stuff based on uniqueuri, set in ViewData.  
    return View();
}

[HttpPost]
[SetTempDataModelState]
public ActionResult Create(Review review)
{
    // validate review
    if (validatedOk)
    {
        return RedirectToAction("Details", new { postId = review.PostId});
    }  
    else
    {
        ModelState.AddModelError("ReviewErrors", "some error occured");
        return RedirectToAction("Create", new { uniqueUri = Request.RequestContext.RouteData.Values["uniqueUri"]});
    }   
}

If you also want to pass the model along in TempData (as bigb suggested) then you can still do that too.

Answer 6

I could use TempData["Errors"]

TempData are passed accross actions preserving data 1 time.