router-query-integration

What this skill does

# Router × Query Integration

Seamlessly integrate TanStack Router with TanStack Query for optimal SPA performance and instant navigation.

## Route Loader + Query Prefetch

The key pattern: Use route loaders to prefetch queries BEFORE navigation completes.

**Benefits:**
- Loaders run before render, eliminating waterfall
- Fast SPA navigations (instant perceived performance)
- Queries still benefit from cache deduplication
- Add Router & Query DevTools during development (auto-hide in production)

## Basic Pattern

```typescript
// src/routes/users/$id.tsx
import { createFileRoute } from '@tanstack/react-router'
import { queryClient } from '@/app/queryClient'
import { usersKeys, fetchUser } from '@/features/users/queries'

export const Route = createFileRoute('/users/$id')({
  loader: async ({ params }) => {
    const id = params.id

    return queryClient.ensureQueryData({
      queryKey: usersKeys.detail(id),
      queryFn: () => fetchUser(id),
      staleTime: 30_000, // Fresh for 30 seconds
    })
  },
  component: UserPage,
})

function UserPage() {
  const { id } = Route.useParams()
  const { data: user } = useQuery({
    queryKey: usersKeys.detail(id),
    queryFn: () => fetchUser(id),
  })

  // Data is already loaded from loader, so this returns instantly
  return <div>{user.name}</div>
}
```

## Using Query Options Pattern (Recommended)

**Query Options** provide maximum type safety and DRY:

```typescript
// features/users/queries.ts
import { queryOptions } from '@tanstack/react-query'

export function userQueryOptions(userId: string) {
  return queryOptions({
    queryKey: ['users', userId],
    queryFn: () => fetchUser(userId),
    staleTime: 30_000,
  })
}

export function useUser(userId: string) {
  return useQuery(userQueryOptions(userId))
}

// src/routes/users/$userId.tsx
import { userQueryOptions } from '@/features/users/queries'
import { queryClient } from '@/app/queryClient'

export const Route = createFileRoute('/users/$userId')({
  loader: ({ params }) =>
    queryClient.ensureQueryData(userQueryOptions(params.userId)),
  component: UserPage,
})

function UserPage() {
  const { userId } = Route.useParams()
  const { data: user } = useUser(userId)

  return <div>{user.name}</div>
}
```

## Multiple Queries in Loader

```typescript
export const Route = createFileRoute('/dashboard')({
  loader: async () => {
    // Run in parallel
    await Promise.all([
      queryClient.ensureQueryData(userQueryOptions()),
      queryClient.ensureQueryData(statsQueryOptions()),
      queryClient.ensureQueryData(postsQueryOptions()),
    ])
  },
  component: Dashboard,
})

function Dashboard() {
  const { data: user } = useUser()
  const { data: stats } = useStats()
  const { data: posts } = usePosts()

  // All data pre-loaded, renders instantly
  return (
    <div>
      <UserHeader user={user} />
      <StatsPanel stats={stats} />
      <PostsList posts={posts} />
    </div>
  )
}
```

## Dependent Queries

```typescript
export const Route = createFileRoute('/users/$userId/posts')({
  loader: async ({ params }) => {
    // First ensure user data
    const user = await queryClient.ensureQueryData(
      userQueryOptions(params.userId)
    )

    // Then fetch user's posts
    return queryClient.ensureQueryData(
      userPostsQueryOptions(user.id)
    )
  },
  component: UserPostsPage,
})
```

## Query Client Setup

**Export the query client for use in loaders:**

```typescript
// src/app/queryClient.ts
import { QueryClient } from '@tanstack/react-query'

export const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 0,
      gcTime: 5 * 60_000,
      retry: 1,
    },
  },
})

// src/main.tsx
import { QueryClientProvider } from '@tanstack/react-query'
import { queryClient } from './app/queryClient'

ReactDOM.createRoot(document.getElementById('root')!).render(
  <StrictMode>
    <QueryClientProvider client={queryClient}>
      <RouterProvider router={router} />
    </QueryClientProvider>
  </StrictMode>
)
```

## Prefetch vs Ensure

**`prefetchQuery`** - Fire and forget, don't wait:
```typescript
loader: ({ params }) => {
  // Don't await - just start fetching
  queryClient.prefetchQuery(userQueryOptions(params.userId))
  // Navigation continues immediately
}
```

**`ensureQueryData`** - Wait for data (recommended):
```typescript
loader: async ({ params }) => {
  // Await - navigation waits until data is ready
  return await queryClient.ensureQueryData(userQueryOptions(params.userId))
}
```

**`fetchQuery`** - Always fetches fresh:
```typescript
loader: async ({ params }) => {
  // Ignores cache, always fetches
  return await queryClient.fetchQuery(userQueryOptions(params.userId))
}
```

**Recommendation:** Use `ensureQueryData` for most cases - respects cache and staleTime.

## Handling Errors in Loaders

```typescript
export const Route = createFileRoute('/users/$userId')({
  loader: async ({ params }) => {
    try {
      return await queryClient.ensureQueryData(userQueryOptions(params.userId))
    } catch (error) {
      // Let router error boundary handle it
      throw error
    }
  },
  errorComponent: ({ error }) => (
    <div>
      <h1>Failed to load user</h1>
      <p>{error.message}</p>
    </div>
  ),
  component: UserPage,
})
```

## Invalidating Queries After Mutations

```typescript
// features/users/mutations.ts
export function useUpdateUser() {
  const queryClient = useQueryClient()
  const navigate = useNavigate()

  return useMutation({
    mutationFn: (user: UpdateUserDTO) => api.put(`/users/${user.id}`, user),
    onSuccess: (updatedUser) => {
      // Update cache immediately
      queryClient.setQueryData(
        userQueryOptions(updatedUser.id).queryKey,
        updatedUser
      )

      // Invalidate related queries
      queryClient.invalidateQueries({ queryKey: ['users', 'list'] })

      // Navigate to updated user page (will use cached data)
      navigate({ to: '/users/$userId', params: { userId: updatedUser.id } })
    },
  })
}
```

## Preloading on Link Hover

```typescript
import { Link, useRouter } from '@tanstack/react-router'

function UserLink({ userId }: { userId: string }) {
  const router = useRouter()

  const handleMouseEnter = () => {
    // Preload route (includes loader)
    router.preloadRoute({ to: '/users/$userId', params: { userId } })
  }

  return (
    <Link
      to="/users/$userId"
      params={{ userId }}
      onMouseEnter={handleMouseEnter}
    >
      View User
    </Link>
  )
}
```

Or use built-in preload:
```typescript
<Link
  to="/users/$userId"
  params={{ userId: '123' }}
  preload="intent" // Preload on hover/focus
>
  View User
</Link>
```

## Search Params + Queries

```typescript
// src/routes/users/index.tsx
import { z } from 'zod'

const searchSchema = z.object({
  page: z.number().default(1),
  filter: z.enum(['active', 'all']).default('all'),
})

export const Route = createFileRoute('/users/')({
  validateSearch: searchSchema,
  loader: ({ search }) => {
    return queryClient.ensureQueryData(
      usersListQueryOptions(search.page, search.filter)
    )
  },
  component: UsersPage,
})

function UsersPage() {
  const { page, filter } = Route.useSearch()
  const { data: users } = useUsersList(page, filter)

  return <UserTable users={users} page={page} filter={filter} />
}
```

## Suspense Mode

With Suspense, you don't need separate loading states:

```typescript
export const Route = createFileRoute('/users/$userId')({
  loader: ({ params }) =>
    queryClient.ensureQueryData(userQueryOptions(params.userId)),
  component: UserPage,
})

function UserPage() {
  const { userId } = Route.useParams()

  // Use Suspense hook - data is NEVER undefined
  const { data: user } = useSuspenseQuery(userQueryOptions(userId))

  return <div>{user.name}</div>
}

// Wrap route in Suspense boundary (in __root.tsx or layout)
<Suspense fallback={<Spinner />}>
  <Outlet />
</Suspense>
```

## Performance Best Practices

1. **Prefetch in Loaders** - Alw