460 lines
10 KiB
Markdown
460 lines
10 KiB
Markdown
# Next.js Data Fetching
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Server-side data fetching, caching strategies, revalidation, and loading patterns.
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## Fetch API Extensions
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Next.js extends native fetch with caching and revalidation:
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```tsx
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// Force cache (default) - cache forever
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fetch('https://api.example.com/data', { cache: 'force-cache' })
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// No cache - fetch on every request
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fetch('https://api.example.com/data', { cache: 'no-store' })
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// Revalidate - cache with time-based revalidation
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fetch('https://api.example.com/data', { next: { revalidate: 3600 } })
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// Tag-based revalidation
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fetch('https://api.example.com/data', { next: { tags: ['posts'] } })
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```
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## Caching Strategies
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### Static Data (Default)
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Fetched at build time, cached indefinitely:
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```tsx
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// app/posts/page.tsx
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async function getPosts() {
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const res = await fetch('https://api.example.com/posts')
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// Same as: fetch(url, { cache: 'force-cache' })
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return res.json()
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}
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export default async function Posts() {
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const posts = await getPosts()
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return <PostsList posts={posts} />
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}
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```
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Use for: Content that rarely changes, static pages
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### Dynamic Data
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Fetched on every request:
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```tsx
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async function getUser() {
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const res = await fetch('https://api.example.com/user', {
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cache: 'no-store'
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})
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return res.json()
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}
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export default async function Profile() {
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const user = await getUser()
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return <div>{user.name}</div>
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}
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```
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Use for: User-specific data, real-time content
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### Incremental Static Regeneration (ISR)
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Revalidate cached data after time period:
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```tsx
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async function getPosts() {
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const res = await fetch('https://api.example.com/posts', {
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next: { revalidate: 60 } // Revalidate every 60 seconds
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})
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return res.json()
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}
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export default async function Posts() {
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const posts = await getPosts()
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return <PostsList posts={posts} />
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}
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```
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How it works:
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1. First request: Generate page, cache it
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2. Subsequent requests: Serve cached page
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3. After 60s: Next request triggers regeneration in background
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4. New page cached, served to subsequent requests
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Use for: News sites, blogs, product listings
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## Revalidation Strategies
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### Time-Based Revalidation
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```tsx
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// Revalidate every hour
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fetch('https://api.example.com/posts', {
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next: { revalidate: 3600 }
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})
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// Revalidate every 10 seconds
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fetch('https://api.example.com/trending', {
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next: { revalidate: 10 }
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})
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```
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### On-Demand Revalidation
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Revalidate specific paths or tags programmatically:
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```tsx
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// app/actions.ts
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'use server'
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import { revalidatePath, revalidateTag } from 'next/cache'
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export async function createPost(formData: FormData) {
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const post = await db.post.create({
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data: {
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title: formData.get('title'),
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content: formData.get('content')
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}
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})
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// Revalidate specific path
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revalidatePath('/posts')
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revalidatePath(`/posts/${post.id}`)
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// Or revalidate by tag
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revalidateTag('posts')
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}
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```
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Tag-based revalidation:
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```tsx
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// Fetch with tags
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async function getPosts() {
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const res = await fetch('https://api.example.com/posts', {
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next: { tags: ['posts', 'content'] }
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})
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return res.json()
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}
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async function getComments(postId: string) {
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const res = await fetch(`https://api.example.com/comments/${postId}`, {
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next: { tags: ['comments', `post-${postId}`] }
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})
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return res.json()
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}
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// Revalidate all 'posts' tagged requests
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revalidateTag('posts')
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// Revalidate specific post comments
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revalidateTag(`post-${postId}`)
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```
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### Route Segment Config
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Configure entire route segment:
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```tsx
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// app/posts/page.tsx
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export const revalidate = 3600 // Revalidate every hour
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export default async function Posts() {
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const posts = await fetch('https://api.example.com/posts').then(r => r.json())
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return <PostsList posts={posts} />
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}
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```
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Options:
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```tsx
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export const dynamic = 'auto' // default
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export const dynamic = 'force-dynamic' // no caching
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export const dynamic = 'error' // error if dynamic
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export const dynamic = 'force-static' // force static
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export const revalidate = false // never revalidate (default)
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export const revalidate = 0 // no cache
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export const revalidate = 60 // revalidate every 60s
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export const fetchCache = 'auto' // default
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export const fetchCache = 'default-cache'
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export const fetchCache = 'only-cache'
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export const fetchCache = 'force-cache'
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export const fetchCache = 'default-no-store'
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export const fetchCache = 'only-no-store'
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export const fetchCache = 'force-no-store'
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```
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## Data Fetching Patterns
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### Parallel Fetching
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Fetch multiple resources simultaneously:
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```tsx
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async function getData() {
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// Start both requests in parallel
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const [posts, users] = await Promise.all([
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fetch('https://api.example.com/posts').then(r => r.json()),
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fetch('https://api.example.com/users').then(r => r.json())
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])
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return { posts, users }
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}
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export default async function Page() {
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const { posts, users } = await getData()
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return (
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<div>
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<PostsList posts={posts} />
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<UsersList users={users} />
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</div>
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)
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}
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```
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### Sequential Fetching
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Fetch dependent data:
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```tsx
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async function getData(postId: string) {
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// Fetch post first
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const post = await fetch(`https://api.example.com/posts/${postId}`).then(r => r.json())
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// Then fetch author based on post data
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const author = await fetch(`https://api.example.com/users/${post.authorId}`).then(r => r.json())
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return { post, author }
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}
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export default async function Post({ params }: { params: { id: string } }) {
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const { post, author } = await getData(params.id)
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return (
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<article>
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<h1>{post.title}</h1>
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<p>By {author.name}</p>
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<div>{post.content}</div>
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</article>
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)
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}
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```
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### Preloading Data
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Optimize sequential waterfalls:
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```tsx
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// lib/data.ts
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import { cache } from 'react'
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export const getUser = cache(async (id: string) => {
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const res = await fetch(`https://api.example.com/users/${id}`)
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return res.json()
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})
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// app/user/[id]/page.tsx
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import { getUser } from '@/lib/data'
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// Preload before component renders
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async function preload(id: string) {
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void getUser(id) // Start fetching immediately
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}
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export default async function User({ params }: { params: { id: string } }) {
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preload(params.id) // Start fetch
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// Render other UI
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const user = await getUser(params.id) // Will use cached result
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return <div>{user.name}</div>
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}
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```
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## Loading States
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### Loading File
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Automatic loading UI:
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```tsx
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// app/dashboard/loading.tsx
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export default function Loading() {
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return <div className="spinner">Loading dashboard...</div>
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}
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// app/dashboard/page.tsx
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export default async function Dashboard() {
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const data = await fetchDashboard()
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return <DashboardView data={data} />
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}
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```
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### Suspense Boundaries
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Granular loading states:
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```tsx
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// app/dashboard/page.tsx
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import { Suspense } from 'react'
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async function Revenue() {
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const data = await fetchRevenue() // 2s
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return <RevenueChart data={data} />
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}
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async function Sales() {
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const data = await fetchSales() // 0.5s
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return <SalesTable data={data} />
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}
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export default function Dashboard() {
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return (
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<div>
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<h1>Dashboard</h1>
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<Suspense fallback={<RevenueChartSkeleton />}>
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<Revenue />
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</Suspense>
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<Suspense fallback={<SalesTableSkeleton />}>
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<Sales />
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</Suspense>
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</div>
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)
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}
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```
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Sales loads after 0.5s, Revenue after 2s - no blocking.
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## Static Generation
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### generateStaticParams
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Pre-render dynamic routes at build time:
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```tsx
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// app/posts/[slug]/page.tsx
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export async function generateStaticParams() {
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const posts = await fetch('https://api.example.com/posts').then(r => r.json())
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return posts.map(post => ({
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slug: post.slug
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}))
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}
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export default async function Post({ params }: { params: { slug: string } }) {
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const post = await fetch(`https://api.example.com/posts/${params.slug}`).then(r => r.json())
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return <article>{post.content}</article>
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}
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```
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Generates static pages at build:
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- `/posts/hello-world`
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- `/posts/nextjs-guide`
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- `/posts/react-tips`
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### Dynamic Params Handling
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```tsx
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// app/posts/[slug]/page.tsx
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export const dynamicParams = true // default - generate on-demand if not pre-rendered
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export const dynamicParams = false // 404 for paths not in generateStaticParams
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```
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## Error Handling
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### Try-Catch in Server Components
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```tsx
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async function getData() {
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try {
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const res = await fetch('https://api.example.com/data')
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if (!res.ok) {
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throw new Error('Failed to fetch data')
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}
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return res.json()
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} catch (error) {
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console.error('Data fetch error:', error)
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return null
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}
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}
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export default async function Page() {
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const data = await getData()
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if (!data) {
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return <div>Failed to load data</div>
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}
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return <DataView data={data} />
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}
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```
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### Error Boundaries
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```tsx
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// app/error.tsx
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'use client'
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export default function Error({
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error,
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reset,
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}: {
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error: Error & { digest?: string }
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reset: () => void
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}) {
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return (
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<div>
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<h2>Something went wrong!</h2>
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<button onClick={() => reset()}>Try again</button>
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</div>
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)
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}
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```
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## Database Queries
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Direct database access in Server Components:
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```tsx
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// lib/db.ts
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import { PrismaClient } from '@prisma/client'
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const prisma = new PrismaClient()
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export async function getPosts() {
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return prisma.post.findMany({
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include: { author: true },
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orderBy: { createdAt: 'desc' }
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})
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}
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// app/posts/page.tsx
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import { getPosts } from '@/lib/db'
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export default async function Posts() {
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const posts = await getPosts()
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return <PostsList posts={posts} />
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}
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```
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## Best Practices
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1. **Default to static** - Use `cache: 'force-cache'` or default behavior
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2. **Use ISR for semi-dynamic content** - Balance freshness and performance
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3. **Fetch in parallel** - Use `Promise.all()` for independent requests
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4. **Add loading states** - Use Suspense for better UX
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5. **Handle errors gracefully** - Provide fallbacks and error boundaries
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6. **Use on-demand revalidation** - Trigger updates after mutations
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7. **Tag your fetches** - Enable granular cache invalidation
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8. **Dedupe automatically** - Next.js dedupes identical fetch requests
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9. **Avoid client-side fetching** - Use Server Components when possible
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10. **Cache database queries** - Use React cache() for expensive queries
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