未做任何更改时出现OptimisticConcurrency异常

在MVC web应用程序中使用实体框架6调用SaveChanges()时，我偶尔会收到OptimisticConcurrency异常，即使我没有更改此执行线程内的任何对象。当然，在不同的线程/进程中进行更改是可能的。OptimisticConcurrency异常似乎是不可能发生的，但是，唉，它经常发生。

var launchedSurvey = DB.Find<LaunchedSurvey>(id);
DB.SaveChanges(); // throws OptimisticConcurrencyException 

我调用SaveChanges，即使没有变化发生简单的测试，因为当添加记录时，我收到了相同的异常，但没有对现有对象发生任何变化……这似乎也不应该抛出OptimisticConcurrencyException。

这是错误信息

System.Exception: TestSave Failed ---> System.Data.Entity.Infrastructure.DbUpdateException: SaveChangesAndReload caught exception and attempted to handle it => attempts:5
 ---> System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception. Handling of exceptions while saving can be made easier by exposing foreign key properties in your entity types. See the InnerException for details. ---> System.Data.Entity.Core.OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on understanding and handling optimistic concurrency exceptions.
   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.ValidateRowsAffected(Int64 rowsAffected, UpdateCommand source)
   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions options, Boolean executeInExistingTransaction)
   at System.Data.Entity.Internal.InternalContext.SaveChanges()

这是LaunchedSurvey的c-tor

public LaunchedSurvey()
{
    CreationTime = DateTime.UtcNow;
    WorkerLaunchedSurveys = new Collection<WorkerLaunchedSurvey>();
    WorkerQualificationRequests = new Collection<WorkerQualificationRequest>();
    _remainingDemographic = new DateTime(1900, 1, 1);
    MinimumPercent = 0.10;
    ExcludeList = new List<LaunchedSurvey>();
    IncludeList = new List<LaunchedSurvey>();
    ScreenedWorkers = new List<ScreenedWorker>();
    EmailMessages = new List<EmailMessage>();
    AssignmentsPendingWorkers = new HashSet<AssignmentsPendingWorker>();
    ExcludedWorkersManual = new List<AmazonWorkerExcluded>();
    IncludedWorkersManual = new List<AmazonWorkerIncluded>();
    PendingWorkersQualificationsUnknown = new List<AmazonWorkerPending>();
    Tags = new List<Tag>();
    ManualQualificationTypeIdList = new List<QualificationType>();
    WorkerSurveyStatisticAuto = new WorkerSurveyStatisticAuto();
    WorkerSurveyStatisticManual = new WorkerSurveyStatisticManual();
    WorkerUniqueIdentifierList = new List<WorkerUniqueIdentifier>();
}

对此的任何见解都非常感谢!