MVC4 and ViewModel - Validation Message not displayed

Question

I'm developing a web application using MVC 4 and Entity Framework. I'm using a ViewModel which represents a Product to create/edit/delete. I have created a validation class which check the entries and displays an error message when it is necessary.

Since I'm using a ViewModel, unfortunately the error messages are not displayed anymore? How should I proceed?

Here's my ViewModel :

public class ProductViewModel
{

    public Product Product { get; set; }

    public ProductType ProductType { get; set; }

    public List<SelectListItem> ProductCompanies { get; set; }
}

Here's my action (create, for example) :

[HttpPost]
public ActionResult Create(ProductViewModel pvm)
{
    pvm.ProductCompanies = db.ProductCompanies.ToList().Select(s => new SelectListItem
    {
        Text = s.Name,
        Value = s.Id_ProductCompany.ToString()
    }).ToList();

    ViewBag.Id_ProductCompany = new SelectList(db.ProductCompanies, "Id_ProductCompany", "Name", pvm.ProductType.Id_ProductCompany);

    if (ModelState.IsValid)
    {

        ModelStateDictionary errors = Validator.isValid(pvm.ProductType);

        if (errors.Count > 0)
        {
            ModelState.Merge(errors);
            return View(pvm);
        }


        Product product = new Product
        {
            PurchaseDate = pvm.Product.PurchaseDate,
            SerialNumber = pvm.Product.SerialNumber,
            Id_ProductType = pvm.ProductType.Id_ProductType
        };

        ProductType productType = new ProductType
        {
            Model = pvm.ProductType.Model,
            CatalogPrice = pvm.ProductType.CatalogPrice,
            Id_ProductCompany = pvm.ProductType.Id_ProductCompany
        };

        db.ProductTypes.AddObject(productType);
        db.Products.AddObject(product);
        db.SaveChanges();
        return RedirectToAction("Index", "Person");    
    }

    return View(pvm);
}

My own validator :

public static ModelStateDictionary isValid(ProductType element)
{
    ModelStateDictionary errors = new ModelStateDictionary();

    if (!Regex.IsMatch(element.Model, @"^[a-zA-Z0-9\s][a-zA-Z-_0-9\s]+$"))
    {
        errors.AddModelError("Model", "Invalid name !");
    }

    return errors;
}

And where the message should be displayed :

<div class="editor-label">
    Model : 
</div>
<div class="editor-field">
    @Html.TextBoxFor(model => model.ProductType.Model, new { maxlength = 50 })
    @Html.ValidationMessageFor(model => model.ProductType.Model)
</div>

Try passing the VM in the Validator: IsValid(pvm) and then add the error like errors.AddModelError("ProductType.Model", "Invalid Name!");. A bit of a random guess here, don't actually know if using the dot will make MVC recognise the erroring field. — Tallmaris
– Tallmaris, Commented Apr 18, 2013 at 12:31

LukLed · Accepted Answer · 2013-04-18 12:34:43Z

2

Maybe changing it to

Maybe `errors.AddModelError("ProductType.Model", "Invalid name !");

would resolve your problem.

By the way, the best solution would be to use DataAnnotations and create your own ValidationAttribute:

public sealed class ValidNameAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        ....check regex here...
    }
}

Then you should decorate Name property with ValidName attribute.

EDIT:

You can also implement IValidatableObject interface in view model. ASP.NET MVC will pick it up and do automatic validation.

public class MyViewModel: IValidatableObject
{   
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (regexFails)
        {
            results.Add(new ValidationResult("Please enter valid name."));
        }
    }
}

edited Apr 18, 2013 at 12:34

answered Apr 18, 2013 at 12:29

LukLed

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2 Comments

Traffy Over a year ago

Your first suggestion is not working, but thanks. However, I will have many fields to check... If I understand well, am I going to create a classe for each field? In my view model, is it impossible to check the regex?

LukLed Over a year ago

@Traffy: Sorry. I made simple mistake. Can you check again?

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