c# - 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. How can I fix this?

 ModelState.AddModelError("_FORM", "Unable to save ticket");
 ModelState.AddModelError("_FORM", "Phone number was invalid.");
 ModelState.AddModelError("_FORM", "Lane number is required.");
 return RedirectToAction("CreateStep", "Ticket");

I know some have suggested using TempData, but how would I get each error out of the ModelState?

Thanks.

Answer 1

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..