Next Cache Components

# Cache Components (Next.js 16+)

Cache Components enable Partial Prerendering (PPR) - mix static, cached, and dynamic content in a single route.

## Enable Cache Components

```ts
// next.config.ts
import type { NextConfig } from 'next'

const nextConfig: NextConfig = {
  cacheComponents: true,
}

export default nextConfig
```

This replaces the old `experimental.ppr` flag.

---

## Three Content Types

With Cache Components enabled, content falls into three categories:

### 1. Static (Auto-Prerendered)

Synchronous code, imports, pure computations - prerendered at build time:

```tsx
export default function Page() {
  return (
    <header>
      <h1>Our Blog</h1>  {/* Static - instant */}
      <nav>...</nav>
    </header>
  )
}
```

### 2. Cached (`use cache`)

Async data that doesn't need fresh fetches every request:

```tsx
async function BlogPosts() {
  'use cache'
  cacheLife('hours')

  const posts = await db.posts.findMany()
  return <PostList posts={posts} />
}
```

### 3. Dynamic (Suspense)

Runtime data that must be fresh - wrap in Suspense:

```tsx
import { Suspense } from 'react'

export default function Page() {
  return (
    <>
      <BlogPosts />  {/* Cached */}

      <Suspense fallback={<p>Loading...</p>}>
        <UserPreferences />  {/* Dynamic - streams in */}
      </Suspense>
    </>
  )
}

async function UserPreferences() {
  const theme = (await cookies()).get('theme')?.value
  return <p>Theme: {theme}</p>
}
```

---

## `use cache` Directive

### File Level

```tsx
'use cache'

export default async function Page() {
  // Entire page is cached
  const data = await fetchData()
  return <div>{data}</div>
}
```

### Component Level

```tsx
export async function CachedComponent() {
  'use cache'
  const data = await fetchData()
  return <div>{data}</div>
}
```

### Function Level

```tsx
export async function getData() {
  'use cache'
  return db.query('SELECT * FROM posts')
}
```

---

## Cache Profiles

### Built-in Profiles

```tsx
'use cache'                    // Default: 5m stale, 15m revalidate
```

```tsx
'use cache: remote'           // Platform-provided cache (Redis, KV)
```

```tsx
'use cache: private'          // For compliance, allows runtime APIs
```

### `cacheLife()` - Custom Lifetime

```tsx
import { cacheLife } from 'next/cache'

async function getData() {
  'use cache'
  cacheLife('hours')  // Built-in profile
  return fetch('/api/data')
}
```

Built-in profiles: `'default'`, `'minutes'`, `'hours'`, `'days'`, `'weeks'`, `'max'`

### Inline Configuration

```tsx
async function getData() {
  'use cache'
  cacheLife({
    stale: 3600,      // 1 hour - serve stale while revalidating
    revalidate: 7200, // 2 hours - background revalidation interval
    expire: 86400,    // 1 day - hard expiration
  })
  return fetch('/api/data')
}
```

---

## Cache Invalidation

### `cacheTag()` - Tag Cached Content

```tsx
import { cacheTag } from 'next/cache'

async function getProducts() {
  'use cache'
  cacheTag('products')
  return db.products.findMany()
}

async function getProduct(id: string) {
  'use cache'
  cacheTag('products', `product-${id}`)
  return db.products.findUnique({ where: { id } })
}
```

### `updateTag()` - Immediate Invalidation

Use when you need the cache refreshed within the same request:

```tsx
'use server'

import { updateTag } from 'next/cache'

export async function updateProduct(id: string, data: FormData) {
  await db.products.update({ where: { id }, data })
  updateTag(`product-${id}`)  // Immediate - same request sees fresh data
}
```

### `revalidateTag()` - Background Revalidation

Use for stale-while-revalidate behavior:

```tsx
'use server'

import { revalidateTag } from 'next/cache'

export async function createPost(data: FormData) {
  await db.posts.create({ data })
  revalidateTag('posts')  // Background - next request sees f