`@defer` gives `TypeError: Cannot read properties of undefined (reading 'length')`

[VinceBT-BG]

This is an example of query:

query listAuthorsWithStats(
	$authorIds: [ID!]
	$startDate: DateTime!
	$endDate: DateTime!
	$timeZone: String!
) {
	listAuthors(
		authorIds: $authorIds
		startDate: $startDate
		endDate: $endDate
	) {
		authors {
			id
			... @defer {
				stats(startDate: $startDate, endDate: $endDate, timeZone: $timeZone) {
					aggregates {
						labels
						value
					}
				}
			}
		}
	}
}

And this is the stacktrace of the error that I get:

[Network]: TypeError: Cannot read properties of undefined (reading 'length')
0:" at eval (webpack-internal:///../../node_modules/.pnpm/@apollo+client@3.12.4_@types+react@18.3.2_graphql@17.0.0-alpha.7.canary.pr.4297.42bcd01f7c733_bwcf472rfi3np7dy47bczsyb6q/node_modules/@apollo/client/utilities/common/incrementalResult.js:38:31)"
1:" at Array.forEach (<anonymous>)"
2:" at mergeIncrementalData (webpack-internal:///../../node_modules/.pnpm/@apollo+client@3.12.4_@types+react@18.3.2_graphql@17.0.0-alpha.7.canary.pr.4297.42bcd01f7c733_bwcf472rfi3np7dy47bczsyb6q/node_modules/@apollo/client/utilities/common/incrementalResult.js:36:28)"
3:" at QueryInfo.markResult (webpack-internal:///../../node_modules/.pnpm/@apollo+client@3.12.4_@types+react@18.3.2_graphql@17.0.0-alpha.7.canary.pr.4297.42bcd01f7c733_bwcf472rfi3np7dy47bczsyb6q/node_modules/@apollo/client/core/QueryInfo.js:274:103)"
4:" at eval (webpack-internal:///../../node_modules/.pnpm/@apollo+client@3.12.4_@types+react@18.3.2_graphql@17.0.0-alpha.7.canary.pr.4297.42bcd01f7c733_bwcf472rfi3np7dy47bczsyb6q/node_modules/@apollo/client/core/QueryManager.js:812:27)"
5:" at both (webpack-internal:///../../node_modules/.pnpm/@apollo+client@3.12.4_@types+react@18.3.2_graphql@17.0.0-alpha.7.canary.pr.4297.42bcd01f7c733_bwcf472rfi3np7dy47bczsyb6q/node_modules/@apollo/client/utilities/observables/asyncMap.js:27:31)"

I have been following the tutorial from here

These are the versions that I use:

"@apollo/client": "^3.12.4"
"graphql": "^17.0.0-alpha.7"

[jerelmiller]

Hey @VinceBT-BG 👋

Apollo Client is only compatible with the 17.0.0-alpha.2 format of @defer responses, so your issue is likely there. Can you try downgrading graphql to 17.0.0-alpha.2 and see if that fixes your issue?

[VinceBT-BG]

It looks like it fixed my issue, thanks
Is there somewhere we can keep track of the evolution of the @defer and @stream features for future production use ?

[jerelmiller]

@VinceBT-BG are you looking to track it from the GraphQL spec itself or Apollo's implementation of it? I'll give you both links anyways 😆

• Apollo's tracking issue for @defer/@stream: Add experimental support for @defer, @stream, and @live apollo-feature-requests#3
• GraphQL discussion on latest changes for incremental delivery format: New response format (June 2023) graphql/defer-stream-wg#69
• Spec edits for incremental delivery: Spec edits for incremental delivery, Section 3 & 7 only graphql/graphql-spec#1124

We're hoping the format is settled sometime soon so that we can update the client to support the newer format from the spec, but we've held off so that we aren't introducing too much churn in the client. I believe alpha.2 is the most popular format in the ecosystem right now, but here's to hoping we are able to move forward sometime soon 🤞

[robrichard]

Hi @jerelmiller, have you had a chance to review the latest incremental delivery response format? I think it would be a big help in moving the proposal forward if we have buy in from the major GraphQL clients. Would you or any other maintainers of apollo-client be willing to review and let us know that the current proposal works for you?

[jerelmiller]

@robrichard I was reading through it this morning, though I'm going to spend some more time with it (apologies, I haven't followed the spec changes super closely up until now). Barring any significant feedback, does it look like this might be the final or close to final version?

We have a team meeting this week to discuss @defer as well so I might have some updates there soon from us.

[robrichard]

@jerelmiller I can't guarantee this will be the final version until the spec edits are accepted, but there haven't been any proposed changes to the response format since the June 2023 version. I'm working now on getting the spec edits reviewed, but getting buy in from the wider graphql ecosystem will help give us confidence to move forward.

[jerelmiller]

@robrichard ok thats great to hear! Thanks for chiming in. I'll try and provide an update if I have one after our meeting this morning.

[jerelmiller]

Ok an update from our end:

We took a look at this as a team and will eventually set some time aside, but it will take a bit of time. We do plan to bake in a defer sprint eventually, but we need to tackle some existing defer issues to get a proper vetting of the new format. We'd also like to bring some internal teams with us which make take a bit of time. We will do our best to get to this as soon as we can but bear with us in the mean time!

[jerelmiller]

Hey all 👋

We've just released the first preview of @stream in 4.1.0-alpha.0 including support for the new incremental format shipped in graphql@17.0.0-alhpa.9. I'd be grateful if you could try it out and provide feedback!

npm i @apollo/client@next

Thanks so much!

---

@robrichard as we get feedback for @stream, I'll let you know if we encounter anything significant. I'm hoping we get some usage here so that we can prove out the format on the client end. Thanks for your patience from us!