Optimistic updates failing seemingly randomly

[gregoralbrecht]

Hey there! 👋 I'm trying to get optimistic updates working with 2 custom hooks, but I must be doing something horribly wrong because some updates just don't appear like I'd expect them to.

For the sake of easy reproduction, I tried finding a public dummy API that supports POST requests, so here's a sandbox: https://codesandbox.io/s/musing-keldysh-s2bmn?file=/src/hooks/useAddPost.ts

More specifically, I have 2 main issues with this:

1. Optimistic updates randomly disappear after being added

I'd expect this to just work fine and it does in like 90% of the time. However, sometimes, the optimistically-added post briefly appears in the list, then disappears again until it's refetched some time later. You can see this by adding some random posts and seeing the described behavior.

2. The query is randomly undefined / doesn't exist

At least in this CodeSandbox, the query is sometimes undefined. Is this due to it being a dev server? Hot module replacement? I honestly don't know, but sometimes queryClient.getQueryData() returns undefined (as mentioned in the docs). Not sure why that is, though, and I don't know how to handle that case for optimistic updates?

I'd much appreciate any help here! 🙃

PS: I already looked at the "Optimistic Updates in TypeScript" example and it seems broken.

PPS: I also wanted to ask this on Discord, but the current link results in a "Unable to accept invite"

[TkDodo]

this seems to be purely an issue with that json placeholder api. We create an entry, and the next fetch sometimes doesn't return that entry 🤷 .

PS: I already looked at the "Optimistic Updates in TypeScript" example and it seems broken.

what's broken there please?

PPS: I also wanted to ask this on Discord, but the current link results in a "Unable to accept invite"

hmm the discord link works for me...

[gregoralbrecht]

seems to be purely an issue with that json placeholder API

Well, that's reassuring then :) Thanks for taking a look! 🙏

what's broken there please?

Sorry for the vague description, seems like I need some sleep. Everything works fine as long as you let CodeSandbox do its thing first.

Do you have any idea why the query cache might get unmounted randomly? #2065 seems to mention the same issue.

[TkDodo]

I answered in that other discussion: #2065 (comment)