Properly handling model validation errors

Question

How do I get this simple form validation going?

I have an AccountVerificationController which originally had the following method:

public ActionResult Index(AccountVerificationModel model)

Problem is when view is initially loaded, there are validation errors since the model has required fields as follows:

 public class AccountVerificationModel
    {
        [Required]        
        public string MerchantId { get; set; }
        [Required]       
        public string AccountNumber { get; set; }
        [Required, StringLength(9, MinimumLength = 9, ErrorMessage = "The Routing Number must be 9 digits")]  
}

However, this is not desired behavior. I want validation to occur only after user clicks on a validate button, so I changed form to invoke the Verify method in the account controller.

View is as follows;

@using (Html.BeginForm("Verify", "AccountVerification", FormMethod.Post))
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h2>@ViewBag.Title</h2>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.SubMerchantId, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.MerchantId, new { htmlAttributes = new { @class = "form-control", placeholder = "MID" } })
                @Html.ValidationMessageFor(model => model.MerchantId, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.RoutingNumber, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.RoutingNumber, new { htmlAttributes = new { @class = "form-control", placeholder = "9 Digit Routing Number" } })
                @Html.ValidationMessageFor(model => model.RoutingNumber, "", new { @class = "text-danger" })
            </div>
        </div>           

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input name="validate" type="submit" value="Validate" class="btn btn-info"/>
            </div>
        </div>
    </div>
}

Now the challenge is handling model validation errors. I have the controller structured as follows:

  public class AccountVerificationController : BaseMvcController
{    

    public AccountVerificationController()
    {
    }    

      public ActionResult Index()
        {            
            return View(new AccountVerificationModel());
        }

    public ActionResult Verify(AccountVerificationModel model)
    {
        // do the validation then re-direct......
        if (!model.IsValid())
        {
            return RedirectToAction("Index", model);
        }

        // otherwise try to validate the account

        if (!model.VerificationSuccessful)
        {
            // repopulate the view with this model...
            return RedirectToAction("Index", model);
        }

        return Redirect("Index");           
    }

However, during re-direction, I am losing the entire context, model errors and all. Reading upon this whole model binding but if someone can quickly spot what I am doing wrong here, that would be appreciated.

Answer 1

Well, you can't redirect when there's errors. Period. Redirection is actually a two-step process, even though it seems to happen seemlessly. First, the server returns a 301 or 302 status code with a header value indicating the URL the client should go to instead. Then, the client issues a brand new request to that given URL. That's why no context is persisted. It's basically the same as the client requesting the page for the very first time.

The only way to maintain the context is to simply return a view. Which means your Verify action would need to return the same view as your Index action. However, that's not exactly ideal. I don't exactly understand what the original problem was that made you decide to add the Verify action in the first place, but that can likely be fixed if you open a new question to that regard. You should really just postback to your Index action.