stackoveflow:24605152

class Program
{
    static void Main(string[] args)
    {


        var context = new TestContext();
        context.Parents.Add(new Parent
        {
            Name = "Parent",
            Child1s = new Collection<Child1>
            {
                new Child1
                {
                    Child2 = new Child2()
                    {
                        Name = "Child2"
                    },
                    Name = "Child1"
                }
            }
        });

        context.SaveChanges();

        Console.ReadKey();
    }

    public class Parent
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        public string Name { get; set; }

        public ICollection<Child1> Child1s { get; set; }
    }

    public class Child1
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        public string Name { get; set; }

        public Child2 Child2 { get; set; }

        public Parent Parent { get; set; }
    }

    public class Child2
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int Id { get; set; }

        public string Name { get; set; }

        public Child1 Child1 { get; set; }
    }

    public class TestContext : DbContext
    {
        static TestContext()
        {
            AppDomain.CurrentDomain.SetData("DataDirectory", @"E:\");
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<TestContext, Migrations.Configuration>());
        }

        public DbSet<Parent> Parents { get; set; }

        public TestContext()
            : base(
                @"Data Source=(LocalDb)\v11.0;AttachDbFilename=|DataDirectory|\CloudComputingDB-20140610.mdf;Initial Catalog=CloudComputingDB-20140610;Integrated Security=True;MultipleActiveResultSets=True;"
                )
        {

        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Child1>().HasRequired(c1 => c1.Child2).WithRequiredPrincipal(c2 => c2.Child1);
            base.OnModelCreating(modelBuilder);
        }
    }
}