Should I use data annotations in domain model too? ASP.NET MVC - asp.net-mvc

Question

I am a newbie in ASP.NET MVC, and something made me confused.
I am creating a login/registration web-app, and when I came to confirm password, I was a bit confused. I surely don't want confirm password column in my database. So for that reason, I use ViewModel. And I use data annotations for validation in my ViewModel. So there is no need to write any validation code in my Domain Model.
But when Entity Framework creates a table from my Domain Model object, from where will it get information for example about how many characters should username take? If I used data annotations in my domain model, I would write MaxLength or something.
Should I validate data in domain model too?

Answer 1

You client side validation can be taken care of using Data Annotations on your View Model and include jQuery validation script in your View.
So in your View Model, you can set minimum password length restriction like this:
using System.ComponentModel.DataAnnotations;
public class RegisterViewModel
{
[Required]
[EmailAddress]
[Display(Name = "Email")]
public string Email { get; set; }
[Required]
[StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
[DataType(DataType.Password)]
[Display(Name = "Password")]
public string Password { get; set; }
[DataType(DataType.Password)]
[Display(Name = "Confirm password")]
[System.ComponentModel.DataAnnotations.Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
public string ConfirmPassword { get; set; }
}
Of course, this is only for client side validation, for server side validation, you have to validate the data in your controller, but i don't believe you have to use data annotation on your domain model.
So in your controller, you can validate the data passed through like this
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Register(RegisterViewModel model)
{
//checks for data passed through, if somehow people bypasses client side validation
if (ModelState.IsValid)
{
//continue
}
//validation failed, return to view
return View(model);
}
ModelState.IsValid indicates if it was possible to bind the incoming values from the request to the model correctly and whether any explicitly specified validation rules were broken during the model binding process. ---- what does this do : ModelState.IsValid