c# - Entity framework multi threading

Question

i want to remove entities on a background thread but we can not delete entities on another thread that it has be created on so how can i do that and keep the ui responding? i'm tying to use the backgroundworker class here is the code

void deletePeriodWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            Thread.Sleep(3000);
            List<Period> selectedPeriods = e.Argument as List<Period>;

            foreach (Period period in selectedPeriods)
            {
                while (period.Transactions.Count > 0)
                {
                    Transaction transaction = period.Transactions[0];
                    this.Dispatcher.Invoke(new Action(() => context.Transactions.Remove(transaction)), 
                        System.Windows.Threading.DispatcherPriority.Normal);
                }

                this.Dispatcher.Invoke(new Action(() => context.Periods.Remove(period)), 
                    System.Windows.Threading.DispatcherPriority.Normal);
            }
            this.Dispatcher.Invoke(new Action(() => context.SaveChanges()),
                    System.Windows.Threading.DispatcherPriority.Normal);
        }

Rang · Accepted Answer · 2014-05-05 03:27:47Z

2

Don't use 'foreach' to delete entities. When you delete a entity,the source is changed, it may throw an exception. Use 'for' instead. And why you delete it in a new thread?UI will be updated when all of the delete operations are finished.

try like this:

UI(List): itemsource={Binding LstTest}

background:

deletePeriodWorker_DoWork() {

        List<Period> selectedPeriods = e.Argument as List<Period>;

        foreach (Period period in selectedPeriods)
        {
            while (period.Transactions.Count > 0)
            {
                //operation
            }

            //ui updating
            this.Dispatcher.Invoke(new Action(() => LstTest.Remove(period)), 
                System.Windows.Threading.DispatcherPriority.Normal);

            //EF updating
            context.Periods.Remove(period);

        }

        //context savechanges

}

edited May 5, 2014 at 3:27

answered May 5, 2014 at 1:36

Rang

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6 Comments

Matti Virkkunen Over a year ago

Seeing that the source is a plain List<T> it can't be changed by deleting entities, so using foreach is perfectly fine and more readable.

Lerner Over a year ago

Rang but what will happen while the entities are being deleted if it takes a while will the ui remain responding?

Rang Over a year ago

Yes you are right.I am not seeing that the code is context.Periods.Remove(XX). We can't add/remove items to the collection in foreach.

Lerner Over a year ago

Hi rang let say i'm deleting 1000 transactions it could take 2/3 seconds so what will be than?

Rang Over a year ago

Motty, Try another way.Don't creat relationship between delete entities and UI updating. UI's itemsource is binding with a list,add/remove it's items in a new thread.Don't delete entites in a new thread.

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