Using [NotMapped] to pass additional info to the view, when following Database first approach

Question

I am working on an asp.net mvc-5 web application, and i am using entity framework 5.0. I have mapped my SQL server database tables which created an .edmx file. now i want to extend the model classes to have additional non-database attributes, so i created a partial class for my model class and i provided an additional attribute as follow:-

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Web;

namespace Test.Models
{

    public partial class User
    {
         [NotMapped]
         public string NonDataBaseColumn { set; get; }
    }
}

so i have these questions:

1. is this a valid approach to pass additional attributes , by defining additional columns inside the partial classes.
2. since i am using database first approach, so do i need to add [NotMapped] data annotation, or the [NotMapped] is only valid when following code-first approach ?
3. could under any situation the NotMapped column (NonDataBaseColumn in my case) get created inside the Databse automatically ?

Answer 1

is this a valid approach to pass additional attributes, by defining additional columns inside the partial classes?

Technically it is, but repeat after me: don't use Entity Framework models as MVC viewmodels, and spread the word.

I still don't get why virtually every tutorial displays this horrible practice which spawns twenty-odd questions like this one a day, but it is not the way it should be done. Domain models are not view models.

Those tutorials probably do that because it works perfectly fine for a "My first TODO WebApp", so they have less code to show and less good development practices to explain, leaving you with the mess when it breaks horribly for anything more complex than that.

For example, try to add a SelectList property to an entity to provide a dropdown with data, then extract your data layer into a DAL library, and be left scratching your head wondering why you have to reference MVC from your DAL.

See also: ASP.NET MVC: using EF entities as viewmodels?

As for your questions on the [NotMapped] attribute: it does exactly what its name and documentation state, it causes the property it's applied to not to be mapped to a database column.