You can easily mark fields for a model which are primary key or are required.
public class User
{
[Key]
public int Id { get; set; }
[Required(ErrorMessage = "Name is mandatory")]
public string Name { get; set; }
public string Telephone { get; set; }
public string Mobile { get; set; }
[Required(ErrorMessage = "Email is mandatory")]
public string Email { get; set; }
}