Get the "Key" for a strongly typed model in the controller

Question

So I am trying to do get the key for a model object in the controller so that I can add a AddModelError to it.

In my view I use

@Html.ValidationMessageFor(model => model.Email)

Whats the equivalent code to get the Key name to add in the controller so it attaches to this ValidationMessage.

Answer 1

You can use an extension that does the same as the HtmlHelpers, and that will work for nested properties:

public static class ModelStateExtensions
{
  public static void AddModelError<TModel>(this ModelStateDictionary dictionary, Expression<Func<TModel, object>> expression, string errorMessage)
  {
    dictionary.AddModelError(ExpressionHelper.GetExpressionText(expression), errorMessage);
  }
}

So you can use it like this:

ModelState.AddModelError<TModel>(i => i.Person.Name, "test");

equivalent to

ModelState.AddModelError("Person.Name", "test");

It will generate the same Id as the Html. In the MVC source they do some extra sanitizing, but with normal names that shouldn't be a problem.

Answer 2

ModelState.AddModelError("Email", "the email is invalid");

But usually that's not something you should be doing manually in your controller but you should be using a validator. For example you could decorate this Email property with some validation data annotation attribute or if you are like me use FluentValidation.NET => this way you shouldn't be asking yourself questions about keys but focus on the actual validation logic.