I have implemented some changes and I'm getting an error.

[edrmonteiro]

The classes now are: public class ApplicationUser : IdentityUser { // HomeTown will be stored in the same table as Users public string HomeTown { get; set; } public virtual ICollection ToDoes { get; set; } public virtual ICollection ToDoes1 { get; set; }

    public virtual MyUserInfo MyUserInfo { get; set; }
}

public class ToDo
{
    public int Id { get; set; }
    public string Description { get; set; }
    public bool IsDone { get; set; }
    public virtual ICollection<ApplicationUser> User { get; set; }
    public virtual ICollection<ApplicationUser> User1 { get; set; }
}

Initialization file now is like: private void InitializeIdentityForEF(MyDbContext context) { var UserManager = new UserManager(new UserStore(context)); var RoleManager = new RoleManager(new RoleStore(context)); var myinfo = new MyUserInfo() { FirstName = "Pranav", LastName = "Rastogi" }; string name = "Admin"; string password = "123456"; string test = "test";

        //Create Role Test and User Test
        RoleManager.Create(new IdentityRole(test));

        var user1 = new ApplicationUser();
        user1.UserName = test;
        user1.HomeTown = "Seattle";
        user1.MyUserInfo = myinfo;
        user1.ToDoes = new List<ToDo>();

        UserManager.Create(user1, password);

        //Create Role Admin if it does not exist
        if (!RoleManager.RoleExists(name))
        {
            var roleresult = RoleManager.Create(new IdentityRole(name));
        }

        //Create User=Admin with password=123456
        var user = new ApplicationUser();
        user.UserName = name;
        user.HomeTown = "Seattle";
        user.MyUserInfo = myinfo;
        user.ToDoes = new List<ToDo>();
        var adminresult = UserManager.Create(user, password);

        //Add User Admin to Role Admin
        if (adminresult.Succeeded)
        {
            var result = UserManager.AddToRole(user.Id, name);
        }

        var todo = new List<ToDo>
        {
            new ToDo { Description = "teste1", IsDone = false, User = new List<ApplicationUser>()},   
            new ToDo { Description = "teste2", IsDone = false, User = new List<ApplicationUser>()},   
        };
        todo.ForEach(s => context.ToDoes.Add(s));
        context.SaveChanges();

        todo[0].User.Add(user);
        context.SaveChanges();

        user.ToDoes.Add(todo[0]);
        context.SaveChanges();
        user.ToDoes.Add(todo[1]);
        context.SaveChanges();

        var count1 = user.ToDoes.Count;         //Here the count is 2
        var count2 = user1.ToDoes.Count;         //Here the count is 0

        user1.ToDoes.Add(todo[0]);
        context.SaveChanges();

        user1.ToDoes.Add(todo[1]);
        context.SaveChanges();

        var count3 = user.ToDoes.Count;         //Here the count is 0
        var count4 = user1.ToDoes.Count;         //Here the count is 2
    }

The error: count1 and count3 must be 2, however when todo[0] and todo[1] are added to user1, they are removed from user todo list. Is this a bug or a error on the code? If I delete ToDoes1 from ApplicationUser class and User1 from ToDo class the error goes away. However my project will need it.

[edrmonteiro]

The problem was solved using modelBuilder.Entity.