Apsync subscription lambda resolver

I have created a mutation and a subscription to that mutation. Unless I did not select a resolver for that subscription - everything is working fine. This is what called local resolver, right?

But, say, I need some logic to be done for data formatting before give it to subscriber. I have added an lambda for that and set it as data source an resolver for this subscription. But this lambda only triggered once - when I creating subscription in graphql playground. Then it newer triggers again as mutation runs again and again.

What might be the reason of such behavior? If this is expected?

I can’t help much beyond confirming that’s how AppSync works. Even AWS has said this.

can you please show a link on where they said this

Not without spending a lot of time searching for one. If you need a link then I would start at the Github issues for aws-amplify or aws-mobile-appsync-sdk-js

can you maybe comment another strange situation I got with subscriptions: - whatever data structure I request in subscription, every time I will only got fields specified in mutation

despite the fact that I chose id in subscription, I will get cost because it was selected in mutation. Is it expected behavior?

This is expected too. Only the fields passed to the mutation are available in the subscription. It’s the way AppSync works.

The subscription is need to have a selection of subfields. There is an error if I don’t select any. But if I do, they just ignored. This all looks very strange…


This also means that I can’t actually control what data would be passed to subscriber. I might have same mutation to be triggered with different subfields by different clients, the single subscriber would have different data in those cases then. Looks inconsistent…