Entity Framework - "New transaction is not allowed because there are other threads running in the session"

Question

I am getting the following error trying to save changes in entity framework -

System.Data.SqlClient.SqlException: New transaction is not allowed because there are other threads running in the session.

I have seen various answers to this problem, but I cannot seem to get any of them to work, basically I am saving a large number of items in a transaction inside my repository, I have to loop through several items to delete them and write an audit record.

All other answers I have seen for this (E.g. Mark Staffords Answer) suggest declaring an explicit transaction (which I have) or by only calling save changes after completing the loop (this is not an option due to the way auditing currently works - the audit ID is required to write the audit details records).

The error is thrown whenever 'SaveChanges' is called inside the delete method, see below -

public virtual void Save(DoseReturn oldDoseReturn)
{
    // Get the datetime when the save started
    DateTime saveStartTime = DateTime.Now;
    Dictionary<string, object> oldValues = new Dictionary<string, object>();
    Dictionary<string, object> newValues = new Dictionary<string, object>();

    // Get the object context and open a new transaction
    ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;
    objectContext.Connection.Open();
    DbTransaction transaction = objectContext.Connection.BeginTransaction();

    // Use the transaction for all updates
    using (transaction)
    {
        if (oldDoseReturn != null)
        {
              IDoseReturnStatusRepository statusRepository = new DoseReturnStatusRepository();
              var list = statusRepository.AsQueryable().Where(x => x.DoseReturnID == oldDoseReturn.DoseReturnID);

              foreach (var item in list)
              {
                  statusRepository.Delete(item, objectRetrievedDateTime, objectContext, saveStartTime, out oldValues, out newValues);
              }

              context.SaveChanges();

              // Get the relevant repository
              IDoseReturnsRepository repository = new DoseReturnsRepository();

              // audit and delete the object
              repository.Delete(oldDoseReturn, objectRetrievedDateTime, objectContext, saveStartTime, out oldValues, out newValues);

              context.SaveChanges();
         }
    }

    try
    {
         // Conduct a final save, then commit the transaction
         context.SaveChanges();
         transaction.Commit();
    }
    catch (Exception ex)
    {
         // An error has occurred, rollback the transaction and close the connection, then present the error
         transaction.Rollback();
         objectContext.Connection.Close();
         throw ex;
    }
    // Close the connection
    objectContext.Connection.Close();
}

public virtual void Delete(T entity, DateTime? objectRetrievedDateTime, ObjectContext objectContext, DateTime saveStartTime, out Dictionary<string, object> oldValues, out Dictionary<string, object> newValues)
    {
        oldValues = new Dictionary<string, object>();
        newValues = new Dictionary<string, object>();

        if (entity == null)
        {
            throw new ArgumentException("Cannot update a null entity.");
        }

        string entityName = entity.GetType().Name;

        if (!objectRetrievedDateTime.HasValue || !this.AuditsAfterRetieval(objectRetrievedDateTime, entityName, entity, saveStartTime))
        {
            this.DeletedEntityAudit(entity, out oldValues, out newValues);

            context.Entry(entity).State = System.Data.EntityState.Deleted;
            this.context.Set<T>().Remove(entity);
            this.Audit(entity, entityName, "Delete", oldValues, newValues, true);
            this.context.SaveChanges();
        }
        else
        {
            throw new Exception("Object cannot be saved as it has been amended in another thread");
        }
    }

Answer 1

This might be because you are enumerating results when trying to save changes.

Try changing this line:

var list = statusRepository.AsQueryable()
               .Where(x => x.DoseReturnID == oldDoseReturn.DoseReturnID);

to:

var list = statusRepository.AsQueryable()
               .Where(x => x.DoseReturnID == oldDoseReturn.DoseReturnID)
               .ToList();

As a side note invoking .SaveChanges() inside a loop is usually not a good idea as it is in general an expensive operation (talks to the database).