Question

I am trying to save my contact, which has references to ContactRelation (just the relationship of the contact, married, single, etc) and Country. But everytime I try to save my contact, which is validated I get the exception ‘ADO.Net Entity Framework An entity object cannot be referenced by multiple instances of IEntityChangeTracker’

public Contact CreateContact(Contact contact) {     _entities.AddToContact(contact); //throws the exception     _entities.SaveChanges();     return contact ; } 

I’m using a loosely coupled MVC design with Services and Repositories. I’ve read a lot of posts about this exception but none give me a working answer…

Thank you, Peter

Answer 1

[Update]
Because L2E is used you need to save all the linked objects first before you can save the main object. Which makes sense otherwise you would create (in my example) an artist without it’s contact object. This isn’t allowed by the database design.
[/Update]

Here’s my implementation which worked.

[AcceptVerbs(HttpVerbs.Post)] public ActionResult Create([Bind(Exclude = 'Id')] Artist artist, [Bind(Prefix = 'Contact')] Contact contact, [Bind(Prefix = 'Country')] Country country, [Bind(Prefix = 'ContactRelationship')] ContactRelationship contactRelationship) {     ViewData['Countries'] = new SelectList(new CountryService(_msw).ListCountries().OrderBy(c => c.Name), 'ID', 'Name');     ViewData['ContactRelationships'] = new SelectList(new ContactRelationshipService(_msw).ListContactRelationships().OrderBy(c => c.ID), 'ID', 'Description');      country = _countryService.GetCountryById(country.ID);     contact.Country = country;     contactRelationship = _contactRelationshipService.GetContactRelationship(contactRelationship.ID);     contact.ContactRelationship = contactRelationship;     if(_contactService.CreateContact(contact)){         artist.Contact = contact;         if (_service.CreateArtist(artist))             return RedirectToAction('Index');             }     return View('Create'); } 

And then in my ContactRepository :

public Contact CreateContact(Contact contact) {     _entities.AddToContact(contact); //no longer throws the exception     _entities.SaveChanges();     return contact ; } 

I also found on this website that it is best to keep the same context throughout the application so I’m now using a special Data class for this:

Rick Strahl and Samuel Maecham have taught me that you should keep your datacontext per user per request. Which means putting it in the HttpContext for web applications. Read all about it here

public class Data {     public static MyDBEntities MyDBEntities     {         get         {             if (HttpContext.Current != null && HttpContext.Current['myDBEntities'] == null)             {                 HttpContext.Current['myDBEntities'] = new MyDBEntities ();             }             return HttpContext.Current['myDBEntities'] as MyDBEntities;         }         set {              if(HttpContext.Current != null)                 HttpContext.Current['myDBEntities'] = value;          }     } }