Caching, stale time e refetch in background

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Dati aggiornati e obsoleti

staleTime

useQuery({
  queryKey: ['users'],
  queryFn: fetchUsers,
  staleTime: 60_000, // fresh for 60 seconds
})

Impostare staleTime per i dati statici

// Effectively never stale — reload only on explicit invalidation
useQuery({ queryKey: ['countries'], queryFn: fetchCountries,
  staleTime: Infinity })

gcTime (garbage collection)

useQuery({
  queryKey: ['products'],
  queryFn: fetchProducts,
  gcTime: 10 * 60 * 1000, // keep in memory for 10 minutes
})

staleTime e gcTime

Indicatori di refetch in background

const { data, isLoading, isFetching } = useQuery({ /* ... */ });

return (
  <>
    {isLoading ? <Spinner /> : <DataView data={data} />}
    {isFetching && !isLoading && <RefreshIndicator />}
  </>
);

refetchOnWindowFocus

useQuery({
  queryKey: ['settings'],
  queryFn: fetchSettings,
  refetchOnWindowFocus: false,
})

refetchInterval per il polling

useQuery({
  queryKey: ['liveStats'],
  queryFn: fetchStats,
  refetchInterval: 5000, // every 5 seconds
})

Dati segnaposto

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

useQuery({
  queryKey: ['posts', page],
  queryFn: () => fetchPage(page),
  placeholderData: keepPreviousData,
})

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