rn-data-fetchinglisted

# 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-setup.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-patte