How to declare one to one relationship using Entity Framework 4 Code First (POCO)

Question

How to declare a one to one relationship using Entity Framework 4 Code First (POCO)?

I found this question (one-to-one relationships in Entity Framework 4) , but the

Answer 1

public class User
{
    public int Id { get; set; }
    public string Username { get; set; }

    public virtual Profile Profile { get; set; }
}

public class Profile
{
    public int Id { get; set; }

    public int UserID { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string PostalCode { get; set; }
}

Add the virtual Profile and the UserID and I think that should get you there.