Cloning entity with EF 6, null reference exception

Question

I am trying to clone an entity (EF 6.x, code first), using the technique here: Entity Framework 5 deep copy/clone of an entity

However, I get a strange NullReference exception when trying to add the cloned ticket to the DbSet:

var clonedTicket = _context.Tickets
          .AsNoTracking()
          .Include(o => o.Lines.Select(l => l.Serials))
          .Include(o => o.Payments.Select(p => p.PayCodeInfo))
          .SingleOrDefault(o => o.TicketId == ticketId);

clonedTicket.TicketId = _context.Tickets.Max(o => o.TicketId) + 1;

foreach (var line in clonedTicket.Lines)
    line.TicketId = clonedTicket.TicketId;

foreach (var payment in clonedTicket.Payments)
    payment.TicketId = clonedTicket.TicketId;

  _context.Tickets.Add(clonedTicket);  <---- System.NullReferenceException
  _context.SaveChanges();

The exception is on _context.Tickets.Add(clonedTicket).

clonedTicket looks perfectly normal, nothing is null that should not be. Of course, both _context and Tickets (the DbSet) are non-null.

Here is the full exception:

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=EntityFramework
  StackTrace:
       at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.MarkForeignKeyPropertiesModified()
       at System.Data.Entity.Core.Objects.DataClasses.EntityReference.AddToNavigationPropertyIfCompatible(RelatedEnd otherRelatedEnd)
       at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.IncludeEntity(IEntityWrapper wrappedEntity, Boolean addRelationshipAsUnchanged, Boolean doAttach)
       at System.Data.Entity.Core.Objects.DataClasses.EntityCollection`1.Include(Boolean addRelationshipAsUnchanged, Boolean doAttach)
       at System.Data.Entity.Core.Objects.DataClasses.RelationshipManager.AddRelatedEntitiesToObjectStateManager(Boolean doAttach)
       at System.Data.Entity.Core.Objects.ObjectContext.AddObject(String entitySetName, Object entity)
       at System.Data.Entity.Internal.Linq.InternalSet`1.<>c__DisplayClassd.<Add>b__c()
       at System.Data.Entity.Internal.Linq.InternalSet`1.ActOnSet(Action action, EntityState newState, Object entity, String methodName)
       at System.Data.Entity.Internal.Linq.InternalSet`1.Add(Object entity)
       at System.Data.Entity.DbSet`1.Add(TEntity entity)
       at TheRepo.CreateCloneFromTicket(Int32 ticketId, String clientIp) in c:\...\TheRepo.cs:line 23
       at TheController.CreateReturn(Int32 ticketId) in c:\...\TheController.cs:line 232
       at lambda_method(Closure , Object , Object[] )
       at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
       at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
       at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
  InnerException: 

What am I missing here?

Answer 1

I got this working. The trick was to set ProxyCreationEnabled = false before retrieving the entity:

_context.Configuration.ProxyCreationEnabled = false;
var returnTicket = _context.Tickets
   .AsNoTracking()
   .Include(o => o.Lines.Select(l => l.Serials))
   .Include(o => o.Payments)
   .SingleOrDefault(o => o.TicketId == ticketId);
_context.Configuration.ProxyCreationEnabled = true;

I cannot say that I fully understand why this is, but I guess it has to do with the lazy loading that EF does when ProxyCreation is enabled (which I do not need/want here, since I am loading the related entities explicitly).