EF5: DB First. Generated Models and Custom Validation

Question

If I use Code First Development Model, I have a full control of my code.
For Example, I have model: User.

public class User {
    [Key]
    public int id { get; set; }

    [StringLength(50, ErrorMessage = "* Length might be less then 50 symbols")]
    [Required(ErrorMessage = "* Login can't be empty")]
    public string Login { get; set; }

    [StringLength(50, ErrorMessage = "* Length might be less then 50 symbols")]
    [Required(ErrorMessage = "* Name can't be empty")]
    public string FirstName { get; set; }

    [StringLength(50, ErrorMessage = "* Length might be less then 50 symbols")]
    [Required(ErrorMessage = "* Last name can't be empty")]
    public string LastName { get; set; }

    [DataType(DataType.EmailAddress)]
    public string Email { get; set; }
    public string Phone { get; set; }
    [Required]
    public DateTime CreatedAt { get; set; }
    [Required]
    public DateTime LastLogin { get; set; }

    public List<Post> PostList { get; set; }

}

I have ability to create my own validation, like at model "User".

In case, if I use DB First Development Model, I need to use ADO.NET Entity Data Model to generate models. I have 3 tables:

I have generated files:

DBContext.edmx
 - DBContext.Context.tt
 - DBContext.Designer.cs
 - DBContext.edmx.diagram
 - DBContext.tt
   - Comment.cs
   - DBContext.cs
   - Post.cs
   - Comment.cs

and code below:

public partial class DBContext : DbContext
{
    public DBContext()
        : base("name=DBContext")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public DbSet<Comment> Comment { get; set; }
    public DbSet<Post> Post { get; set; }
    public DbSet<User> User { get; set; }
}

public partial class User
{
    public User()
    {
        this.Comment = new HashSet<Comment>();
        this.Comment1 = new HashSet<Comment>();
        this.Post = new HashSet<Post>();
        this.Post1 = new HashSet<Post>();
    }

    public int id { get; set; }
    public string Login { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
    public System.DateTime CreatedAt { get; set; }
    public System.DateTime LastLogin { get; set; }

    public virtual ICollection<Comment> Comment { get; set; }
    public virtual ICollection<Comment> Comment1 { get; set; }
    public virtual ICollection<Post> Post { get; set; }
    public virtual ICollection<Post> Post1 { get; set; }
    public virtual User User1 { get; set; }
    public virtual User User2 { get; set; }
}

public partial class Post
{
    public Post()
    {
        this.Comment = new HashSet<Comment>();
    }

    public int id { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }
    public string TextFormatted { get; set; }
    public System.DateTime CreatedAt { get; set; }
    public System.DateTime UpdatedAt { get; set; }
    public Nullable<int> CreatedById { get; set; }
    public Nullable<int> UpdatedById { get; set; }
    public Nullable<int> UserId { get; set; }

    public virtual User User { get; set; }
    public virtual User User1 { get; set; }
    public virtual ICollection<Comment> Comment { get; set; }
}

public partial class Comment
{
    public int id { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }
    public string TextFormatted { get; set; }
    public System.DateTime CreatedAt { get; set; }
    public System.DateTime UpdatedAt { get; set; }
    public Nullable<int> CreatedById { get; set; }
    public Nullable<int> UpdatedById { get; set; }
    public Nullable<int> PostId { get; set; }

    public virtual User User { get; set; }
    public virtual User User1 { get; set; }
    public virtual Post Post { get; set; }
    public virtual Comment Comment1 { get; set; }
    public virtual Comment Comment2 { get; set; }
}

Questions:
1. As I understand, if I use DB First Development Model, I can't use my own models for data access, just models/classes, generated by ADO.NET Entity Data Model?
I tried to use my own model "UserOwn" except generated "User", so I got an error "Unable to retrieve metadata for 'TestDBFirst02.Models.UserOwn'". Expected.
2. Can I use both Development Model: Code First and DB First inside one project?
3. If I need to use generated models, what I need to do, when I want to use my own validation? I tried to modificate generated model, and it works:

[StringLength(50, ErrorMessage = "* Length might be less then 50 symbols")]
[Required(ErrorMessage = "* Login can't be empty")]
public string Login { get; set; } 

But, if I need to update model from DB, of course my validation code overwrites by ADO.NET Entity Data Model and attributes disappear. How can I overcome the situation with my own validation?

Answer 1

Answer the 3-rd question: need to use [MetadataTypeAttribute(typeof(UserValidation)] attribute and create validation class, so code is:

[MetadataType(typeof(UserValidation))]
public partial class User {}

public class UserValidation
{
    [StringLength(50, ErrorMessage = "* Length might be less then 50 symbols")]
    [Required(ErrorMessage = "* Login can't be empty")]
    public string Login { get; set; }
}

with the same! namespace, as User model has.
Read more:

• http://www.asp.net/mvc/tutorials/mvc-5/database-first-development/enhancing-data-validation
• http://jnye.co/Posts/19/adding-validation-to-models-created-by-entity-framework-database-first-c
• http://weblogs.asp.net/scottgu/asp-net-mvc-2-model-validation
• Database First Validation
• Adding validation to model with Database First model (EF 5)
• http://www.elevenwinds.com/data-validation-in-asp-net-mvc-database-first