Correlate events with extrinsics in a utility.batch call in Polkadot

Question

In Polkadot and Kusama emitted module events has the phase property so we can correlate them with the extrinsic that triggered that event but I can not do the same when the extrinsic is included in a utility.batch (https://polkadot.js.org/docs/substrate/extrinsics#batchcalls-veccall) extrinsic (as far as I know all the events are related to the utility.batch call so you can not correlate them individually).

Is there a way to correlate an event with the related extrinsic included in a utility.batch call?

Answer 1

The utility.batch call emits events which allow you to organize which extrinsic events are coming from each extrinsic.

Between each call, you should see an Event::ItemCompleted after an extrinsic as successfully completed, or a Event::BatchInterrupted if one of the items in the batch caused the whole batch to stop. After the whole batch is done, you will see Event::BatchCompleted.

You can see an example of that here: https://polkadot.subscan.io/extrinsic/8997424-2

Here you can see ItemCompleted between the crowdloan contribution (the first extrinsic), the memo being updated (the second extrinsic).

So it is just a matter of using these as delimiters, and organizing the events to the appropriate sub-batch call.