Rn Data Fetching

rn-data-fetching — guardrail for data fetching in React Native + Expo

For the current Expo API and per-version details, verify against the Expo docs / MCP mcp.expo.dev / expo/skills (see rn-fundamentals → Source of truth).

The 5 rules (non-negotiable)

1. TanStack Query is the default for any data that comes from the network. fetch + useEffect is acceptable ONLY in didactic examples or for one-off bootstrap calls (e.g. reading a config at app start).
2. One QueryClient per app, mounted at the root layout. Never instantiate per-screen.
3. Query keys are arrays, hierarchical, with the most specific filter last: ["posts", "list", { filter }]. NEVER stringly-typed keys.
4. Every mutation invalidates the queries it affects. Use queryClient.invalidateQueries({ queryKey: [...] }) in onSuccess. Optimistic updates use onMutate + onError rollback.
5. staleTime ≥ 60_000 ms is the default to avoid refetch-on-focus storms. Tune per query based on freshness need.

Quick decision tree

• "Should I use fetch or TanStack Query?" → references/decision-tree.md
• "How do I set up TanStack Query in a fresh Expo app?" → references/tanstack-query-rn.md
• "What's the right query key shape, the right cancel pattern, the right loading state?" → references/patterns.md
• "Show me a working query / mutation / infinite scroll example" → references/examples/
• "Why does my fetch race on unmount?" → references/concepts.md

Common anti-patterns (NEVER do)

• ❌ useEffect(() => { fetch(...).then(setData) }, []) for production data — no retry, no dedup, no cancel.
• ❌ useState<Data | null>(null) + useState<boolean>(false) for loading — let TanStack Query own server state.
• ❌ queryKey: "posts" as a string — must be an array.
• ❌ Calling setData after the component unmounts — TanStack Query handles cancel automatically.
• ❌ Mutation that updates the server but does NOT invalidateQueries — UI shows stale data.
• ❌ Refetching on every navigation — set staleTime per query.

Sources

• Course: codewithbeto.dev/rnCourse — lesson 7 "Fetching Data from an API" + lesson 8 "Rendering Lists and TypeScript" (free).
• Official: https://tanstack.com/query/v5/docs/framework/react/overview
• Official: https://tanstack.com/query/v5/docs/framework/react/guides/mutations
• Official: https://docs.expo.dev/develop/development-builds/use-development-builds/