Make undefined an illegal cache value (for successful queries)

[TkDodo]

Please see this discussion

This is an ever-recurring issue that you can't bail out of updates with setQueryData. But because the updater function gives you a potentially undefined value (if there is no cache entry for the key yet), TypeScript is very unhappy because you're supposed to create a new cache entry, and there is no "bailing out of it" because react-query actually creates the cache entry before the functional updater of setQueryData is called.

Proposed solution

As stated here:

• let's allow the setQueryData functional updater to return undefined
  • signature: T | ((prev: T | undefined) => T | undefined)
  • if undefined is returned, we do not create or update the cache entry
  • that means if we have a previous value and undefined is returned - undefined is not written to the cache, and observers are not informed about that.
  • this is technically breaking if undefined is a legit cache entry value for someone

This would be in-ine with what the initialData function already does: if undefined is returned from that, it is not persisted to the cache.

Also, if a fetch function returns undefined, we should:

• transform it to a failed promise (error)
• warn during development mode about it

[kayvaninvemo]

I face the same issue, I guess that the following code should be valid code:

      queryClient.setQueryData("Key", old => old);

[neongreen]

While we're at it: what should the type of setQueriesData be? If it only traverses existing queries, I guess it should use Updater<TData, TData> and not Updater<TData | undefined, TData> or Updater<TData | undefined, TData | undefined> (the latter is what the linked PR gives).

[TkDodo]

@neongreen A query could exist but still have undefined data in the cache, e.g. if it's in idle or error state. So the latter is correct.

[tannerlinsley]

🎉 This issue has been resolved in version 4.0.0-alpha.11 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[tannerlinsley]

🎉 This issue has been resolved in version 4.0.0-beta.1 🎉

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot 📦🚀