Can conflicting/related mutations be consolidated?

[PabloRomanH]

I'm adopting an offline-first approach on my website with optimistic updates everywhere where it's possible.

I'm finding that when offline, many mutations can be created that could be reduced to a much smaller number of mutations, because they are just updating the same value. I'm finding two patterns of types of mutations that would be great to be able to join into fewer calls to the backend:

• Consecutive mutations that update the same value. In this case, only the last one should be executed.
• Cumulative mutations. Each mutation adds a certain amount to a value. By adding up the amounts in all the mutations that are waiting to be executed, I can calculate a total amount to be added, and replace all of them with a single mutation.

Is this possible?

[TkDodo]

It's an interesting request. Currently, we just execute all paused mutations, one after the other, via resumePausedMutations():

query/packages/query-core/src/mutationCache.ts

Lines 163 to 180 in aa94bdd

	resumePausedMutations(): Promise<unknown> {
	this.#resuming = (this.#resuming ?? Promise.resolve())
	.then(() => {
	const pausedMutations = this.#mutations.filter((x) => x.state.isPaused)
	return notifyManager.batch(() =>
	pausedMutations.reduce(
	(promise, mutation) =>
	promise.then(() => mutation.continue().catch(noop)),
	Promise.resolve() as Promise<unknown>,
	),
	)
	})
	.then(() => {
	this.#resuming = undefined
	})
	return this.#resuming
	}

I thought about adding a muationFilter to that function, and while this would work (I think), the other mutations would still remain in the cache in paused state and might be resumed at another time. Also, we call that function, not you :/

So I think what you'd have to do is hook into the mutationCache and delete / consolidate mutations on your own. I think you could subscribe to the mutationCache, listen to events and then manipulate the cache, e.g. by calling remove on older mutations. You might have to tag them with a muationKey so that you know which ones belong together ...