Question

I am having issues with my application. I have a db table for a print queue. When I read from that table in a loop, once I add that record to the view model, I then want to delete it from the database…this would be the most efficient way to do it, but EF barks:

An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

I’ve tried using multiple contexts… but that didn’t seem to work either. I’ve seen articles like Rick Strahl’s, but frankly it was above my level of understanding, and not exactly sure if it helps my issue here and seemed quite an in depth solution for something as simple as this.

Is there a simple way to accomplish what I am trying to achieve here?

Here is my code:

public List<InventoryContainerLabelViewModel> CreateLabelsViewModel(int intFacilityId)
        {
            var printqRep = new Repository<InventoryContainerPrintQueue>(new InventoryMgmtContext());
            var printqRepDelete = new Repository<InventoryContainerPrintQueue>(new InventoryMgmtContext());
            IQueryable<InventoryContainerPrintQueue> labels = 
                printqRep.SearchFor(x => x.FacilityId == intFacilityId);

            List<InventoryContainerLabelViewModel> labelsViewModel = new List<InventoryContainerLabelViewModel>();

            if (labels.Count() > 0)
            {
                //Get printq record
                foreach (InventoryContainerPrintQueue label in labels)
                {
                    IEnumerable<InventoryContainerDetail> icDtls = 
                        label.InventoryContainerHeader.InventoryContainerDetails;

                    //Get print details
                    foreach (InventoryContainerDetail icDtl in icDtls)
                    {
                        labelsViewModel.Add(new InventoryContainerLabelViewModel()
                            {
                                ...
                                populate view model here
                            }
                        );//Add label to view model

                    } //for each IC detail

                    //Delete the printq record
                    printqRepDelete.Delete(label); <======== Error Here

                } //foreach label loop
            }//label count > 0
            return labelsViewModel.ToList();
        }

Answer 1

In the end, I added a column to the printq table for status, then in the the loop updated it to processed, then called a separate method to delete it.

public List<InventoryContainerLabelViewModel> CreateLabelsViewModel(int intFacilityId)
    {
        InventoryMgmtContext dbContext = new InventoryMgmtContext();
        var printqRep = new Repository<InventoryContainerPrintQueue>(dbContext);

        IEnumerable<InventoryContainerPrintQueue> unprintedPrtqRecs = 
            printqRep.SearchFor(x => x.FacilityId == intFacilityId && x.Printed == false);

        List<InventoryContainerLabelViewModel> labelsViewModel = new List<InventoryContainerLabelViewModel>();

        if (unprintedPrtqRecs.Count() > 0)
        {
            //Get printq record
            foreach (InventoryContainerPrintQueue unprintedPrtqRec in unprintedPrtqRecs)
            {
                IEnumerable<InventoryContainerDetail> icDtls = 
                    unprintedPrtqRec.InventoryContainerHeader.InventoryContainerDetails;

                //Get container details to print
                foreach (InventoryContainerDetail icDtl in icDtls)
                {
                    labelsViewModel.Add(new InventoryContainerLabelViewModel()
                        {
                            ...
                        }
                    );//Get IC details and create view model
                } //for each IC detail

                unprintedPrtqRec.Printed = true;
                printqRep.Update(unprintedPrtqRec, unprintedPrtqRec, false);

            } //foreach label loop

            //Commit updated to Printed status to db
            dbContext.SaveChanges();

        }//label count > 0
        return labelsViewModel;
    }

    public ActionConfirmation<int> DeletePrintQRecs(int intFacilityId)
    {
        InventoryMgmtContext dbContext = new InventoryMgmtContext();
        var printqRep = new Repository<InventoryContainerPrintQueue>(dbContext);

        IEnumerable<InventoryContainerPrintQueue> printedPrtqRecs =
            printqRep.SearchFor(x => x.FacilityId == intFacilityId && x.Printed == true);

        foreach (InventoryContainerPrintQueue printedPrtqRec in printedPrtqRecs)
        {
            //Delete the printq record
            printqRep.Delete(printedPrtqRec, false);
        }

        //Save Changes on all deletes
        ActionConfirmation<int> result;
        try
        {
            dbContext.SaveChanges();
            result = ActionConfirmation<int>.CreateSuccessConfirmation(
                        "All Label Print Q records deleted successfully.",
                        1);
        }
        catch (Exception ex)
        {
            result = ActionConfirmation<int>.CreateFailureConfirmation(
                string.Format("An error occured attempting to {0}. The error was: {2}.",
                        "delete Label Print Q records",
                        ex.Message),
                        1
                        );
        }

        return result;
    }