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walmartlabs / lacinia

GraphQL implementation in pure Clojure
http://lacinia.readthedocs.io/en/latest/
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Feature request - add post-hook to source-stream #201

Closed henryw374 closed 2 years ago

henryw374 commented 6 years ago

Hi,

I need to run some code after the query has been executed in source-stream and I don't see any way of doing this in lacinia currently. In my case, a query-scoped, in-memory cache needs flushing.

As a workaround, I've copy/pasted the innards of the source-stream callback to my own code (so my code puts the result into response-data-ch) and I've added the hook I need after the query result is delivered.

Any thoughts?

Thanks, Henry

oliyh commented 6 years ago

I think this issue belongs in lacinia-pedestal?

But while it's here... A pre-hook would be useful too. For queries we get to use interceptors to do set up and tear down but with subscriptions we only have set-up and tear down per websocket connection. For use cases like per-query metrics, cache life cycles etc it would be useful to have pre and post query hooks.

Thanks

hlship commented 6 years ago

It seems to me, that this logic can live inside the streamer.

It is invoked at the correct time to set up your cache.

It provides a shutdown callback to clean things up when either side of the conversation shuts down. That's where you clear your cache.

henryw374 commented 6 years ago

Hi, thanks for picking this up.

Actually what we need here is query-scoped hooks. For example, we want a query run to have it's own (level 1) cache, to provide consistency for that query result, and after that query has run, flush results to a level 2 cache.

I have sketched an implementation.. What I've done so far would be a breaking change but it just illustrates what we need. If you're happy with the idea, I could keep working on it to make a PR.

hlship commented 2 years ago

I'm sorry this has dragged on so long, the ideas are fine, but it got ignored. Please re-open if this is still something that would be helpful. I would consider a more general system where callback functions could be registred with Lacinia to cover more of the lifecycle of queries and subscriptions.

henryw374 commented 2 years ago

Ok Thanks. I think we still have the copied-over-code-plus-hack doing its thing in our app.

I don't have the time or inclination work on anything more general atm.