State Management with Zustand and React QueryLesson 6.3

React Query: fetching and caching server data

TanStack Query setup, QueryClient, QueryClientProvider, useQuery hook, queryKey, queryFn, loading and error states, automatic refetching, staleTime, cacheTime

React Query for Server State

React Query (TanStack Query) manages server state: fetching, caching, synchronizing, and updating. It replaces useEffect data fetching with built-in handling for loading, errors, refetching, and stale data.

npm install @tanstack/react-query

Setup

import { QueryClient, QueryClientProvider } from '@tanstack/react-query';

const queryClient = new QueryClient();

function App() {
  return (
    <QueryClientProvider client={queryClient}>
      <Router />
    </QueryClientProvider>
  );
}

useQuery

import { useQuery } from '@tanstack/react-query';

function UserList() {
  const { data, isLoading, isError, error } = useQuery({
    queryKey: ['users'],
    queryFn: () => fetch('/api/users').then(r => r.json()),
    staleTime: 60 * 1000, // 60 seconds before refetch
  });

  if (isLoading) return <p>Loading...</p>;
  if (isError) return <p>Error: {error.message}</p>;

  return <ul>{data.map(u => <li key={u.id}>{u.name}</li>)}</ul>;
}

React Query caches by queryKey. Multiple components using the same key share one request. After staleTime elapses, React Query refetches in the background when the window refocuses or the component remounts.