Basic example of EF Code First w/ MVC...

EfCodeFirstExample.cs

public class Thing
{
    [Key]
    public int Id { get; set; }

    public int ParentThingId { get; set; }
    public virtual ParentThing Parent { get; set; }
}

public class ThingConfiguration : EntityTypeConfiguration<Thing>
{
    // Tells EF how to map the relationship...
    public ThingConfiguration()
    {
        this.HasRequired(t => t.Parent).WithMany().HasForeignKey(t => t.ParentThingId);
    }
}

public class ParentThing
{
    [Key]
    public int Id { get; set; }

    public virtual ICollection<Thing> Things { get; set; }
}

public class ParentThingConfiguration : EntityTypeConfiguration<ParentThing>
{
    // Nothing needed here to map the relationship with Thing, 
    // but we need this class to add to the data context implementation
    public ParentThingConfiguration()
    {
        // More mappings to other objects as needed here...
    }
}

public class ThingContext : DbContext
{
    public DbSet<Thing> Things { get; set; }
    public DbSet<ParentThing> ParentThings { get; set; }

    // DbModelBuilder is just ModelBuilder if you're not using the latest version of Code First
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new ThingConfiguration());
        modelBuilder.Configurations.Add(new ParentThingConfiguration());
    }
}

public class ThingController : Controller
{
    private readonly IThingRepository repository;

    public ThignController(IThingRepository repository)
    {
        this.repository = repository;

        // AutoMapper FTW
        Mapper.CreateMap<ThingViewModel, Thing>();
    }

    [HttpPost]
    public ActionResult CreateThing(ThingViewModel model)
    {
        if (ModelState.IsValid)
        {
            var parentThing = repository.GetParentThingById(model.ParentThingId);
            var thing = Mapper.Map<ThingViewModel, Thing>(model);

            // Here comes the "magic". I'd really like to rip this out, but I needed it 
            // to get my tests passing. However, when I step through this and inspect the
            // parentThing object, it never seems to be null when it's attached to 
            // the current ThingContext. It only ever seems to be null when I'm using
            // a mocked repository.
            if (parentThing.Things == null)
            {
                parentThing.Things = new List<Thing>();
            }

            parentThing.Things.Add(thing);
            repository.Save();

            return RedirectToAction("w00t");
        }

        TempData["Thing"] = model;
        return RedirectToAction("TryAgain");
    }
}