We ran into a snag with using the new default Data Annotations Validation in ASP.Net MVC 2.0 Preview 2. Maybe it isn’t a snag, but it is not the behavior I would have expected.

Take the following model:

public class Person
{
  public string ID { get; set; }

  public string FirstName { get; set; }
  public string LastName { get; set; }

  [Required (ErrorMessage = "Required")]
  public string EmailAddress { get; set; }
}

Pretty straight forward, but if you post this form:

    <form action="/person/edit" method="post">
        <input type=hidden name="id" id="id" value="" />
        <input type="text" id="firstname" name="firstname" /> 
        <input type="text" id="lastname" name="lastname" /> 
        <input type="submit" />
    </form> 

To this controller action:

[HttpPost] public virtual ActionResult Edit(Person data)
{
   if (!ModelState.IsValid) throw new ItBrokeException();
   return View();
}

Personally, I would expect every post of that form to show up as invalid, but infact, it is always true. Add the following input to the form and it works.

   <input type="text" id="emailaddress" name="emailaddress" /> <br/>

After that, the ModelState.IsValid returns false, like it should.