Add KeepPreviousData and more control over the cache.

[oSethoum]

Can you please add KeepPreviousData for placeholder to both useQuery and useInfiniteQuery for the purpose of preserving the current data while fetching when for example search or any other param change.

Also if you can add a way to configure the caching, for example sometimes i want to cache to an sqlite database for complete offline use.

[jezsung]

I'll look into adding the keepPreviousData option. I didn't implement it since it has been removed from TanStack Query V5 but this option may be necessary as Flutter Query does not support callback argument for the placeholder option. TanStack Query V5, written in TypeScript, supports a callback argument via union type which was the reason why TanStack Query team has removed the keepPreviousData option.

I have intentionally hid the QueryCache from the public API to keep it internal and not to introduce breaking changes too often. Caching to an SQLite database seems to be another concern which could be supported via data persistence. The QueryCache is designed to be used only for in-memory caching to allow sharing the same query state across widget trees.

TanStack Query is trying to provide data persistence through a separate API, not QueryCache. I have attempted to bring similar feature to Flutter Query but it's not trivial. I'm expecting it to take some time to implement this feature.

[oSethoum]

Thank you for taking the consideration, looking forward to see the feature.