Data Fetching (App Router)

Priority: P0 (CRITICAL)

Fetch data directly in Server Components using async/await.

Fetch API Extensions

Next.js extends the native fetch API for granular caching control.

• Static (Default): fetch('https://api.com') -> cache: 'force-cache'. Built at build time.
• Dynamic: fetch('...', { cache: 'no-store' }). Fetched on every request.
• Revalidated (ISR): fetch('...', { next: { revalidate: 60 } }). Cached for 60s.

Patterns

• Colocation: Fetch data where it's used. Next.js automatically deduplicates requests for the same URL in the same render pass.
• Parallel: Use Promise.all() to prevent waterfalls.

tsx const [user, posts] = await Promise.all([getUser(), getPosts()]);

• Blocking: To prevent UI blocking, wrap the component in <Suspense> and stream the result.

Revalidation

• Path: revalidatePath('/blog/[slug]') - Purges cache for specific route.
• Tag: revalidateTag('collection') - Purges all fetches tagged with next: { tags: ['collection'] }.

Client-Side Fetching (Live Data)

Server Components are the default, but for live/user-specific data that doesn't need SEO:

• SWR / TanStack Query: PREFERRED over useEffect. Handles caching, polling, and deduplication automatically.

```tsx 'use client'; import useSWR from 'swr';

// Good: "Stale-While-Revalidate" - Fast UI, then updates const { data } = useSWR('/api/user', fetcher); ```

• Anti-Pattern: Do not use useEffect to fetch data if you can avoid it. It causes "Flash of Loading Content" and waterfalls.

Anti-Patterns

• API Routes: Don't fetch your own API Routes (/api/...) from Server Components. Call the DB/Service function directly.