Creating custom data annotation validation in MVC 3

Question

For instance, I have an Employee view model. When creating an employee, I want to validate the username to make sure it doesn\'t exist.

public class Employee         


        

Answer 1

I would suggest looking at remote validation. The example even matches your case.

Basically, add the remote attribute to your viewmodel property that points to a controller action

[Remote("IsUserExists", "Account", ErrorMessage = "Can't add what already exists!")]
[Required(ErrorMessage = "Username is required")]
[DisplayName("Username")]
public string Username { get; set; }

which does your work

public ActionResult IsUserExists(string userName) 
{
 if (!UserService.UserNameExists(userName) || (CurrentUser.UserName == userName))
 {
      return "Ok.";
 }
}