Compositionsrouter Query

CRITICAL: For SSR, create QueryClient inside the createRouter factory function. A module-level singleton leaks data between server requests.

Setup: QueryClient in Router Context

Basic (Client-Only)

// src/main.tsx
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
import {
  RouterProvider,
  createRouter,
  createRootRouteWithContext,
} from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

// Root route declares that router context includes queryClient
// (root route file creates it with createRootRouteWithContext — see below)

const queryClient = new QueryClient()

const router = createRouter({
  routeTree,
  defaultPreloadStaleTime: 0, // Let Query manage caching
  context: { queryClient },
  Wrap: ({ children }) => (
    <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
  ),
})

declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}

function App() {
  return <RouterProvider router={router} />
}

Root Route with Context

// src/routes/__root.tsx
import { createRootRouteWithContext, Outlet } from '@tanstack/react-router'
import type { QueryClient } from '@tanstack/react-query'

// Double parentheses: factory pattern
export const Route = createRootRouteWithContext<{
  queryClient: QueryClient
}>()({
  component: () => <Outlet />,
})

SSR-Safe Setup

// src/router.tsx
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
import { createRouter } from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

export function createAppRouter() {
  // Fresh QueryClient per request — prevents data leaking between SSR requests
  const queryClient = new QueryClient()

  return createRouter({
    routeTree,
    defaultPreloadStaleTime: 0,
    context: { queryClient },
    Wrap: ({ children }) => (
      <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
    ),
  })
}

declare module '@tanstack/react-router' {
  interface Register {
    router: ReturnType<typeof createAppRouter>
  }
}

SSR with setupRouterSsrQueryIntegration

For automatic SSR dehydration/hydration and streaming:

npm install @tanstack/react-router-ssr-query

// src/router.tsx
import { QueryClient } from '@tanstack/react-query'
import { createRouter } from '@tanstack/react-router'
import { setupRouterSsrQueryIntegration } from '@tanstack/react-router-ssr-query'
import { routeTree } from './routeTree.gen'

export function createAppRouter() {
  const queryClient = new QueryClient()

  const router = createRouter({
    routeTree,
    defaultPreloadStaleTime: 0,
    context: { queryClient },
  })

  setupRouterSsrQueryIntegration({
    router,
    queryClient,
    // wrapQueryClient: true (default — wraps with QueryClientProvider)
    // handleRedirects: true (default — handles redirect() from queries)
  })

  return router
}

The integration:

• Dehydrates query state on the server and hydrates on the client automatically
• Streams queries that resolve during server render to the client
• Handles redirect() thrown from queries/mutations

Manual SSR Dehydration/Hydration (Without SSR Query Package)

// src/router.tsx
import { QueryClient, dehydrate, hydrate } from '@tanstack/react-query'
import { QueryClientProvider } from '@tanstack/react-query'
import { createRouter } from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

export function createAppRouter() {
  const queryClient = new QueryClient()

  return createRouter({
    routeTree,
    defaultPreloadStaleTime: 0,
    context: { queryClient },
    dehydrate: () => ({
      queryClientState: dehydrate(queryClient),
    }),
    hydrate: (dehydrated) => {
      hydrate(queryClient, dehydrated.queryClientState)
    },
    Wrap: ({ children }) => (
      <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
    ),
  })
}

Core Pattern: ensureQueryData in Loader + useSuspenseQuery in Component

This is the recommended pattern. The loader ensures data is in the cache before render (no loading flash). The component subscribes to the cache for updates.

// src/routes/posts.tsx
import { queryOptions, useSuspenseQuery } from '@tanstack/react-query'
import { createFileRoute } from '@tanstack/react-router'

interface Post {
  id: string
  title: string
}

const postsQueryOptions = queryOptions({
  queryKey: ['posts'],
  queryFn: (): Promise<Array<Post>> =>
    fetch('/api/posts').then((r) => r.json()),
})

export const Route = createFileRoute('/posts')({
  loader: ({ context }) => {
    // ensureQueryData returns cached data if available, fetches if not in cache
    // To also refetch stale data, pass revalidateIfStale: true
    return context.queryClient.ensureQueryData(postsQueryOptions)
  },
  component: PostsPage,
})

function PostsPage() {
  // useSuspenseQuery subscribes to cache — gets background updates
  const { data: posts } = useSuspenseQuery(postsQueryOptions)

  return (
    <ul>
      {posts.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  )
}

With Dynamic Params

// src/routes/posts/$postId.tsx
import { queryOptions, useSuspenseQuery } from '@tanstack/react-query'
import { createFileRoute } from '@tanstack/react-router'

interface Post {
  id: string
  title: string
  content: string
}

const postQueryOptions = (postId: string) =>
  queryOptions({
    queryKey: ['posts', postId],
    queryFn: () => fetch(`/api/posts/${postId}`).then((r) => r.json()),
  })

export const Route = createFileRoute('/posts/$postId')({
  loader: ({ context, params }) => {
    return context.queryClient.ensureQueryData(postQueryOptions(params.postId))
  },
  component: PostPage,
})

function PostPage() {
  const { postId } = Route.useParams()
  const { data: post } = useSuspenseQuery(postQueryOptions(postId))

  return <article>{post.title}</article>
}

Streaming Pattern: prefetchQuery (Not Awaited)

For non-critical data, start the fetch without blocking navigation:

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

export const Route = createFileRoute('/dashboard')({
  loader: ({ context }) => {
    // Await critical data
    const user = context.queryClient.ensureQueryData(userQueryOptions)

    // Start non-critical fetch without awaiting — streams during SSR
    context.queryClient.prefetchQuery(analyticsQueryOptions)

    return user
  },
  component: Dashboard,
})

function Dashboard() {
  // Critical: suspense (data ready immediately)
  const { data: user } = useSuspenseQuery(userQueryOptions)

  // Non-critical: regular query (shows loading state)
  const { data: analytics, isLoading } = useQuery(analyticsQueryOptions)

  return (
    <div>
      <h1>Welcome {user.name}</h1>
      {isLoading ? <Skeleton /> : <AnalyticsChart data={analytics} />}
    </div>
  )
}

Error Handling with useQueryErrorResetBoundary

import { useEffect } from 'react'
import { useQueryErrorResetBoundary } from '@tanstack/react-query'
import { useRouter } from '@tanstack/react-router'

export const Route = createFileRoute('/posts')({
  loader: ({ context }) =>
    context.queryClient.ensureQueryData(postsQueryOptions),
  errorComponent: PostsErrorComponent,
  component: PostsPage,
})

function PostsErrorComponent({
  error,
  reset,
}: {
  error: Error
  reset: () => void
}) {
  const router = useRouter()
  const queryErrorResetBoundary = useQueryErrorResetBoundary()

  useEffect(() => {
    queryErrorResetBoundary.reset()
  }, [queryErrorResetBoundary])

  return (
    <div>
      <p>{error.message}</p>
      <button onClick={() => router.invalidate()}>Retry</button>
    </div>
  )
}

Common Mistakes

1. HIGH: Not setting defaultPreloadStaleTime to 0

Router has a built-in preload cache (default staleTime for preloads is 30s). This prevents Query from controlling data freshness during preloading.

// WRONG — Router's preload cache serves stale data, Query never refetches
const router = createRouter({ routeTree })

// CORRECT — disable Router's preload cache, let Query manage freshness
const router = createRouter({
  routeTree,
  defaultPreloadStaleTime: 0,
})

2. HIGH: Creating QueryClient outside createRouter for SSR

A module-level singleton QueryClient is shared across all server requests, leaking user data between requests.

// WRONG — shared across SSR requests
const queryClient = new QueryClient()
export function createAppRouter() {
  return createRouter({
    routeTree,
    context: { queryClient },
  })
}

// CORRECT — new QueryClient per createAppRouter call
export function createAppRouter() {
  const queryClient = new QueryClient()
  return createRouter({
    routeTree,
    context: { queryClient },
  })
}

3. MEDIUM: Awaiting prefetchQuery in loader blocks rendering

prefetchQuery is designed to fire-and-forget. Awaiting it blocks the navigation transition until the data resolves, defeating the purpose of streaming.

// WRONG — blocks navigation, no streaming benefit