ASP.NET MVC data annotate domain model in the web project - asp.net-mvc

Question

I've seen somewhere how to do this before on a blog but I forgot where or how. Lets say I have a domain in a class library. I'd like to data annotate the properties of this domain as my viewmodel in the web project.
How do I accomplish this?
For example. This domain is in my class library:
public class Person {
public int Id {get; set;}
public string FirstName {get; set;}
}
In my web project, there is this:
//Do i need to set some attribute here?
public class CreatePersonViewModel{
[Required()]
[DisplayName("First Name")]
public string FirstName {get; set;}
}
This code can be mapped to Person without a tool. Probably partial or something.

Answer 1

The whole idea of using a view model is to decouple it from your domain model and to have something which is adapted to the needs of the view. The view model should be declared in the web project and contain all the necessary properties and formatting attributes that this particular view might require. The domain model shouldn't be polluted with any view specific data annotations. So if your model looks like this:
public class Person {
public int Id { get; set; }
public string FirstName { get; set; }
}
You could have the following view model:
public class CreatePersonViewModel {
[Required]
[DisplayName("First Name")]
public string FirstName { get; set; }
}
and then have the controller fetch the model from some repository, map it to the view model (AutoMapper can help you here) and pass the view model to the view.

Answer 2

Do you mean annotate your Domain objects or your view model objects?
Using the System.ComponentModel.DataAnnotations validation attributes (and deriving any of your own from ValidationAttribute, you can validate values bound to the properties of your viewmodel at the point of model binding.
Scott Guthrie has a detailed blog post about Model validation with data annotation validation attributes.
EDIT: you say in a comment to another poster that your types already exist. You can add the MetadataTypeAttribute to the existing type to indicate another type that holds the validation logic to be applied to the properties of your existing type.

Answer 3

You can create a 'buddy' class for your data annotation attributes
[MetadataType(typeof(ResourceMetadata))]
public partial class Resource
{
public object Value { get; set; }
}
public class ResourceMetadata
{
// The metadata class can define hints
[UIHint("ResourceValue")]
public object Value { get; set; }
}

Answer 4

Are you talking about this type of thing?:
using System.ComponentModel.DataAnnotations;
public MyClass
{
[DisplayName("Street Address")]
public string StreetAddress { get; set; }
}
EDIT:
If you need to add Data Annotations to generated class like an Entity do this:
using System.ComponentModel.DataAnnotations;
using System.ComponentModel;
namespace Something
{
[MetadataType(typeof(MetaMyClass))]
public partial class MyClass
{
//You can just leave this empty if you have nothing additional to add to the class
}
public class MetaMyClass
{
[DisplayName("Street Address")]
public string StreetAddress { get; set; }
}
}