EF4.1 : How to deal with items being added to an Object's collection

I'm using EF4.1 for the first time (so be patient with me) but I just cant get to grips with how I can add new items to a sub collection of an object and then save the object.

For example, with the classes below, I can initially save the TravelTicket (containing multiple People) into my database, but as soon as I add a new person and then try to save the TravelTicket again I get:

An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.

Can anyone help?

public class TravelTicket
{
  public int Id { get; set; }
  public string Destination { get; set; }
  public virtual List<Person> Members { get; set; }
}

public class Person
{
  public int Id { get; set; }
  public string Name{ get; set; }
}

EDITED: All relevant code added as requested:

Domain Models:

public class TravelTicket
{
    public int Id { get; set; }
    public string Destination { get; set; }
    public virtual ICollection<Person> Members { get; set; }
}

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

The DB Context:

public class TicketContext : DbContext
{
    public TicketContext()
        : base("TicketStore")
    { }

    public DbSet<TravelTicket> TravelTickets { get; set; }
    public DbSet<Person> People { get; set; }
}

The Repository (relevant methods only):

public class TicketRepository : ITicketRepository
{

    TicketContext context = new TicketContext();

    public void InsertOrUpdate(TravelTicket quoteContainer)
    {
        if (quoteContainer.Id == default(int))
        {
            // New entity
            context.TravelTickets.Add(quoteContainer);
        }
        else
        {
            // Existing entity
            context.Entry(quoteContainer).State = EntityState.Modified;
        }
    }

    public void Save()
    {
        try
        {
            context.SaveChanges();
        }
        catch (DbEntityValidationException dbEx)
        {
            foreach (var validationErrors in dbEx.EntityValidationErrors)
            {
                foreach (var validationError in validationErrors.ValidationErrors)
                {
                    Trace.开发者_开发技巧TraceInformation("Property: {0} Error: {1}", validationError.PropertyName, validationError.ErrorMessage);
                }
            }
        }
    }
}

public interface ITicketRepository
{
    void InsertOrUpdate(TravelTicket travelTicket);
    void Save();
}

The consuming (example) MVC Controller code:

public class TicketSaleController : Controller
{
    private readonly ITicketRepository ticketRepository;

    public TicketSaleController()
        : this(new TicketRepository())
    {
    }

    public TicketSaleController(ITicketRepository ticketRepository)
    {
        this.ticketRepository = ticketRepository;
    }

    public ActionResult Index()
    {
        TravelTicket ticket = new TravelTicket();
        ticket.Destination = "USA";
        List<Person> travellers = new List<Person>();
        travellers.Add(new Person { Name = "Tom" });
        travellers.Add(new Person { Name = "Dick" });
        travellers.Add(new Person { Name = "Harry" });
        ticket.Members = travellers;

        ticketRepository.InsertOrUpdate(ticket);
        ticketRepository.Save();

        Session["Ticket"] = ticket;
        return RedirectToAction("Next");
    }

    public ActionResult Next()
    {
        TravelTicket ticket = (TravelTicket)Session["Ticket"];
        ticket.Members.Add(new Person { Name = "Peter" });
        ticket.Members.Add(new Person { Name = "Paul" });
        ticketRepository.InsertOrUpdate(ticket);
        ticketRepository.Save();
        return View();
    }
}

The call "ticketRepository.InsertOrUpdate(ticket);" on the "Next" method causes the exception:

An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.

FURTHER EDIT: If I pull the object back from the database after its been saved instead of pulling the object from the session, adding the 2 new persons works OK:

Works: TravelTicket ticket = ticketRepository.Find(ticketId); ticket.Members.Add(new Person { Name = "Peter" }); ticket.Members.Add(new Person { Name = "Paul" }); ticketRepository.InsertOrUpdate(ticket); ticketRepository.Save();

Doesn't Work: TravelTicket ticket = (TravelTicket)Session["Ticket"]; ticket.Members.Add(new Person { Name = "Peter" }); ticket.Members.Add(new Person { Name = "Paul" }); ticketRepository.InsertOrUpdate(ticket); ticketRepository.Save();

I'd need to see the code you are using to add items and then persist them. Until that a few generic advice.

It seems like you're using a long-living context to do your stuff. It's a good practice to use short living context, like this:

• Instance context
• Do a single operation
• Dispose the context

Rinse and repeat for every operation you have to do. While following this good practice, you could be indirectly solving your problem.

Again, for more specific help, please post the code you're using ;)

In your mapping class for person, you may need do something like this

 Property(p => p.Id)
            .StoreGeneratedPattern = StoreGeneratedPattern.Identity;