Tanstack Query

TanStack Query v5 (React)

Setup

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

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 60 * 1000, // 1 min (default is 0)
      gcTime: 5 * 60 * 1000, // 5 min (default)
      retry: 3,              // 3 retries with exponential backoff (default)
      refetchOnWindowFocus: true, // default
    },
  },
})

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

Important Defaults

Key recommendation: Set staleTime above 0 to control refetch frequency rather than disabling individual refetch triggers.

queryOptions — co-locate key + fn

Always use queryOptions to define query configurations. It enables type inference across useQuery, prefetchQuery, getQueryData, and setQueryData.

import { queryOptions, infiniteQueryOptions } from '@tanstack/react-query'

export function todosOptions(filters: TodoFilters) {
  return queryOptions({
    queryKey: ['todos', filters],
    queryFn: () => fetchTodos(filters),
    staleTime: 5 * 1000,
  })
}

// Works everywhere with full type inference:
useQuery(todosOptions({ status: 'done' }))
useSuspenseQuery(todosOptions({ status: 'done' }))
queryClient.prefetchQuery(todosOptions({ status: 'done' }))
queryClient.setQueryData(todosOptions({ status: 'done' }).queryKey, newData)
const cached = queryClient.getQueryData(todosOptions({ status: 'done' }).queryKey)
//    ^? TodoItem[] | undefined

For infinite queries, use infiniteQueryOptions (same pattern, adds initialPageParam and getNextPageParam).

useQuery

const {
  data,              // TData | undefined
  error,             // TError | null
  status,            // 'pending' | 'error' | 'success'
  isPending,         // no cached data yet
  isError,
  isSuccess,
  isFetching,        // queryFn is running (including background refetch)
  isLoading,         // isPending && isFetching (first load only)
  isPlaceholderData, // showing placeholder, not real data
  isStale,
  refetch,
  fetchStatus,       // 'fetching' | 'paused' | 'idle'
} = useQuery({
  queryKey: ['todos', userId],  // unique cache key (Array)
  queryFn: () => fetchTodos(userId),
  enabled: !!userId,            // disable until userId exists
  staleTime: 60_000,
  select: (data) => data.filter(t => !t.done), // transform/filter
  placeholderData: keepPreviousData,            // smooth pagination
})

Query states: status tells you "do we have data?"; fetchStatus tells you "is the queryFn running?". They are orthogonal — a query can be pending + paused (no data, no network).

Query Keys

Keys must be Arrays. They are hashed deterministically.

// Object key order does NOT matter — these are equivalent:
useQuery({ queryKey: ['todos', { status, page }] })
useQuery({ queryKey: ['todos', { page, status }] })

// Array item order DOES matter — these are different:
useQuery({ queryKey: ['todos', status, page] })
useQuery({ queryKey: ['todos', page, status] })

Rule: If your queryFn depends on a variable, include it in the queryKey. The key acts as a dependency array.

useMutation

const queryClient = useQueryClient()

const mutation = useMutation({
  mutationFn: (newTodo: CreateTodoInput) => api.post('/todos', newTodo),
  onSuccess: (data, variables) => {
    // Invalidate related queries to trigger refetch
    queryClient.invalidateQueries({ queryKey: ['todos'] })
    // Or update cache directly with response data
    queryClient.setQueryData(['todos', data.id], data)
  },
  onError: (error, variables, onMutateResult) => {},
  onSettled: (data, error, variables, onMutateResult) => {},
})

// Trigger:
mutation.mutate({ title: 'New todo' })

// Or with per-call callbacks:
mutation.mutate(input, { onSuccess: () => navigate('/todos') })

// Async variant (returns Promise):
const data = await mutation.mutateAsync(input)

Lifecycle: onMutate → mutationFn → onSuccess/onError → onSettled. Callbacks returning promises are awaited.

Gotcha: Per-call mutate() callbacks only fire for the latest call if mutations overlap. Use useMutation-level callbacks for reliable logic.

Query Invalidation

// Prefix match (default) — invalidates ['todos'] and ['todos', { page: 1 }]
queryClient.invalidateQueries({ queryKey: ['todos'] })

// Exact match only
queryClient.invalidateQueries({ queryKey: ['todos'], exact: true })

// Predicate for fine-grained control
queryClient.invalidateQueries({
  predicate: (query) => query.queryKey[0] === 'todos' && query.queryKey[1]?.version >= 10,
})

// ALL queries
queryClient.invalidateQueries()

Invalidation marks queries as stale and triggers background refetch for active (rendered) queries.

Optimistic Updates

Approach 1: Via the UI (simpler, recommended)

Render optimistic state from variables directly in JSX:

const { mutate, variables, isPending, isError } = useMutation({
  mutationFn: (text: string) => api.post('/todos', { text }),
  onSettled: () => queryClient.invalidateQueries({ queryKey: ['todos'] }),
})

// In JSX:
{todos.map(todo => <li key={todo.id}>{todo.text}</li>)}
{isPending && <li style={{ opacity: 0.5 }}>{variables}</li>}

Access pending mutations from other components with useMutationState:

const pendingTodos = useMutationState<string>({
  filters: { mutationKey: ['addTodo'], status: 'pending' },
  select: (mutation) => mutation.state.variables,
})

Approach 2: Via cache (with rollback)

useMutation({
  mutationFn: updateTodo,
  onMutate: async (newTodo, context) => {
    await context.client.cancelQueries({ queryKey: ['todos'] })
    const previous = context.client.getQueryData(['todos'])
    context.client.setQueryData(['todos'], (old) => [...old, newTodo])
    return { previous }
  },
  onError: (err, newTodo, onMutateResult, context) => {
    context.client.setQueryData(['todos'], onMutateResult.previous)
  },
  onSettled: (data, error, variables, onMutateResult, context) => {
    context.client.invalidateQueries({ queryKey: ['todos'] })
  },
})

Always cancelQueries before optimistic update to prevent background refetches from overwriting.

Infinite Queries

const {
  data,               // { pages: T[], pageParams: unknown[] }
  fetchNextPage,
  fetchPreviousPage,
  hasNextPage,        // true when getNextPageParam returns non-null/undefined
  hasPreviousPage,
  isFetchingNextPage,
  isFetchingPreviousPage,
} = useInfiniteQuery({
  queryKey: ['projects'],
  queryFn: ({ pageParam }) => fetchProjects(pageParam),
  initialPageParam: 0,     // REQUIRED
  getNextPageParam: (lastPage, allPages) => lastPage.nextCursor ?? undefined,
  maxPages: 3,             // optional: cap cached pages
})

// Render all pages:
{data.pages.map((page, i) => (
  <Fragment key={i}>
    {page.items.map(item => <div key={item.id}>{item.name}</div>)}
  </Fragment>
))}

// Load more:
<button => fetchNextPage()} disabled={!hasNextPage || isFetchingNextPage}>
  {isFetchingNextPage ? 'Loading...' : hasNextPage ? 'Load More' : 'No more'}
</button>

Gotcha: data is { pages, pageParams }, not flat data. initialData and placeholderData must match this shape.

Paginated Queries (keep previous data)

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

const { data, isPlaceholderData } = useQuery({
  queryKey: ['projects', page],
  queryFn: () => fetchProjects(page),
  placeholderData: keepPreviousData,
})

// Prefetch next page for instant transitions:
queryClient.prefetchQuery({
  queryKey: ['projects', page + 1],
  queryFn: () => fetchProjects(page + 1),
})

Prefetching

// In event handlers (hover/focus):
const prefetch = () => queryClient.prefetchQuery(todosOptions())
<button

// In components (avoid Suspense waterfalls):
function Layout({ id }: { id: string }) {
  usePrefetchQuery(commentsOptions(id)) // starts fetch immediately
  return (
    <Suspense fallback="Loading...">
      <Article id={id} />
    </Suspense>
  )
}

// Prefetch infinite queries:
queryClient.prefetchInfiniteQuery({
  ...projectsInfiniteOptions(),
  pages: 3, // prefetch first 3 pages
})

Dependent Queries

const { data: user } = useQuery({
  queryKey: ['user', email],
  queryFn: () => getUserByEmail(email),
})

const { data: projects } = useQuery({
  queryKey: ['projects', user?.id],
  queryFn: () => getProjectsByUser(user!.id),
  enabled: !!user?.id, // waits for user query
})

Type-safe disabling with skipToken:

import { skipToken } from '@tanstack/react-query'

const { data } = useQuery({
  queryKey: ['projects', userId],
  queryFn: userId ? () => getProjects(userId) : skipToken,
})

skipToken prevents refetch() from working — use enabled: false if you need manual refetch.

setQueryData — immutability

// WRONG — mutating cache in place
queryClient.setQueryData(['todo', id], (old) => {
  if (old) old.title = 'new' // DO NOT DO THIS
  return old
})

// CORRECT — return new object
queryClient.setQueryData(['todo', id], (old) =>
  old ? { ...old, title: 'new' } : old
)

Further Reference

• Full API signatures (useQuery, useMutation, useInfiniteQuery, QueryClient): See references/api-reference.md
• SSR & Next.js (hydration, App Router, streaming): See references/ssr-nextjs.md
• Testing (renderHook, mocking, setup): See references/testing.md
• Advanced patterns (TypeScript, Suspense, waterfalls, network modes): See references/advanced-patterns.md