Coalescing multiple load() calls

[ovaris]

I'd like to use Dataloader with await's, but the problem is that batching doesn't work, I guess it has something to do with ticks & event loop. Could someone give me a working example where I could use await's to call load() functions so that it would still use batching?

A simple test.js script:

const DataLoader = require('dataloader')

const testLoader = new DataLoader((ids) => {
  console.log('testLoader', ids)
  return Promise.resolve(ids)
})

const dummyFunction = async () => {
  await testLoader.load(1) // <--- DOES NOT BATCH
  await testLoader.load(2)

  await Promise.all([testLoader.load(3), testLoader.load(4)]) // <-- BATCHES
}

;(async () => {
  await dummyFunction()
})()

output:

node --version
v16.20.2
node test.js
testLoader [ 1 ]
testLoader [ 2 ]
testLoader [ 3, 4 ]

I have a async Express handler function where I'd like to use loader with await's to load stuff from DB, so really basic stuff.
Any tips appreciated!

[joewestcott]

If you use the await keyword, execution will pause at that step until completion, hence, no batching.

[ardatan]

You cannot expect batching to work in your scenario. To understand better, you can ask this question "What if first await's result is needed in the following?"

  const res =  await testLoader.load(1) 
  await testLoader.load(res)

So it is not possible to use batching like that.

[ovaris]

Yeah, thanks, makes perfectly sense, closing this issue.