Question

I am posting a form in an asp.net-mvc page. Here is my controller action:

    public ActionResult UpdateData(MyFormObject entity)
    {
        bool isValid = IsValid(entity);

        if (!isValid)
        {
            var firstError = ModelState.Values.SelectMany(v => v.Errors).First();
            throw new HttpException(404, firstError.ErrorMessage);
        }
        return Json(BuildResult(entity));
    }

Even thought the post passes all of my explicit validation logic, when i check ModelState I see errors. I am seeing errors in ModelState when any of my properties are empty. Here is my object:

public class MyFormObject 
{
    public int Id{ get; set; }
    public int TestId{ get; set; }
    public int OtherId{ get; set; }
}

and I am looking at Model.State and i see errors for any element in my object that is not populated.

If I change this to (NOTE: the “?”)

public class MyFormObject 
{
    public int? Id{ get; set; }
    public int? TestId{ get; set; }
    public int? OtherId{ get; set; }
}

then i no longer get any errors. Is there some default validation that is happening here that I am not setting. I am trying to figure out what is setting ModelState errors in the first case above.

Answer 1

As @Maxim V. Pavlov said, when you post, ASP.MVC engine will try to validate the model, ie its class, and based on class you cited as example, the properties don’t accepts a null or empty value, then it will throw an exception and ModelState will be invalid.

You can see more here @ Validating Model Data in an MVC Application and here ModelStateDictionary.IsValid Property