Cloudflare Developers•3w ago

Nested steps

Heya 👋 quick question to confirm my understanding: do nested steps behave identical to non-nested ones with regards to cache usage after failures? Specifically, if a nested step fails, would the cached results from all parent steps be reused? Or is the caching of parent steps tied to the success of the (most) inner step(s) somehow?

10 Replies

Seekerdasbatatas•3w ago

by nested steps, you mean this?

await step.do('outer', async () => {
  await step.do('inner', async () => {

  })
})

await step.do('outer', async () => {
  await step.do('inner', async () => {

  })
})

Timo ReimannOP•3w ago

Yes

Seekerdasbatatas•3w ago

This is a pattern that I don't know if I would recommend to use 😅 - but I think that the caching of the parent steps are tied to the success of the inner ones

Timo ReimannOP•3w ago

Hmm yeah it guess it's not super useful when the outer and inner steps' fates are tied (which actually makes sense to be the case).

Seekerdasbatatas•3w ago

for curiosity’s sake, why do you want to do nested steps?

Timo ReimannOP•3w ago

The use case I have in mind is where you invoke an external API that returns a list, and then for each result or so you may need to invoke another API. Trying to think how to model that best and wondered if nesting would be helpful here or not.

Seekerdasbatatas•3w ago

then I would do something like this:

const results = step.do('get list', async () => {
  return ["this", "is", "a", "list", "of", "results"]
})

await Promise.all(results.map((val) => step.do(`call another api for: ${val}`, async () => {
  return await fetch('another-api-call')
}))

const results = step.do('get list', async () => {
  return ["this", "is", "a", "list", "of", "results"]
})

await Promise.all(results.map((val) => step.do(`call another api for: ${val}`, async () => {
  return await fetch('another-api-call')
}))

you also get concurrency (for I/O tasks) for free in this case 🙂

Timo ReimannOP•3w ago

Nice, that looks elegant. I suppose that would cache succeeded steps at the per-val level even if one of the many calls eventually failed?

Seekerdasbatatas•3w ago

yes, exactly

Timo ReimannOP•3w ago

Great, thanks Luís.

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Nested steps