Cannot access a disposed object

[fiyazbinhasan]

I'm getting this error where it's telling me that my context is already disposed so I cant access it anymore. I've this trigger implemented in my Order.cs class, which basically updates the order status,

static Order()
{
    Triggers<Bill>.Inserted += async e =>
    {
        await PaymentStatusChangeNotifierAsync(e);
    };
}

Following is the PaymentStatusChangeNotifierAsync code,

private static async Task<int> PaymentStatusChangeNotifierAsync(IEntry<Bill, Microsoft.EntityFrameworkCore.DbContext> e)
{
    Task.Factory.StartNew(() =>
    {
        var orderedItems = e.Context.Entry(e.Entity.Order)
                                .Collection(o => o.OrderItems).Query()
                                .Where(wi => wi.OrderId == e.Entity.OrderId);

        var paidAmountSumation = e.Entity.Order.Bills.Sum(b => b.PaidAmount);

        var orderedItemAmountSumation = orderedItems.Sum(oi => oi.Quantity * (oi.UnitPrice - oi.Discount));

        if (paidAmountSumation == 0)
            e.Entity.Order.PaymentStatus = PaymentStatus.Unpaid;
        else if (paidAmountSumation == orderedItemAmountSumation)
            e.Entity.Order.PaymentStatus = PaymentStatus.Paid;
        else
            e.Entity.Order.PaymentStatus = PaymentStatus.PartialPaid;
    }).Wait();

    return await e.Context.SaveChangesAsync();
}

The await PaymentStatusChangeNotifierAsync(e); occasionally gives me the following exception.

Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application.

Is there any problems with my trigger implementation?

[NickStrupat]

Hi Fiyaz!

The issue is that your trigger handler is asynchronous and at the moment this library does not support that.

Also, I'm curious why you're creating a new Task inside your asynchronous handler?

You get the error sometimes because the context is disposed after it is used, but your handler may still be trying to run in some other thread. Since your handler makes use of the e.Context object, it may or may not be disposed by the time your handler code runs. Basically this is thread-unsafe.

Some simple fixes are:

• Inside your asynchronous handler code, create a new context instance and use that one
  • NOTE: you're doing payment stuff here, which should definitely be in one single transaction... so don't use this option
• Make your handler code synchronous
  • Have all your handlers synchronous and use the e.Context object which keeps it as one transaction
  • Outside of the handler (where you actually add Bill objects to your context, call the SaveChangesAsync so the entire transaction is run outside your calling thread.

Cheers.

[fiyazbinhasan]

I think i get the idea. Sorry I left the Task.Factory.StartNew in the code. Actually I was trying different things to get rid of that problem. But now I know that the handlers can't be asynchronous! Thanks @NickStrupat 👍