Data Fetching

Overview

This skill covers server-side data fetching and caching patterns using Next.js 16+ Cache Components approach with Partial Prerendering (PPR). It combines fine-grained caching control with server-side data fetching for optimal performance.

Core Principles

Data Access Rules

• NEVER call Drizzle ORM directly - Always use server actions defined in lib/actions/
• Cache at the component level - Use the use cache directive in pages/layouts, not in action files
• Wrap dynamic content - Use Suspense boundaries to separate static and dynamic content
• Use lifetime profiles - Always specify cacheLife() with appropriate profile

Cache Components Workflow

1. Planning Data Fetching

Before implementing:

• Identify what data is needed for the page/component
• Determine what content should be instantly visible (cached) vs. what can stream (dynamic)
• Locate the appropriate server actions in lib/actions/ or create new ones if needed
• Plan cache tags for data that needs manual invalidation

2. Implementing Cached Data Fetching

Follow this pattern in pages or layouts:

import { cacheLife } from 'next/cache'
import { getModels } from '@/lib/actions/models'

export default async function ModelsPage() {
  'use cache'
  cacheLife('hours')

  const models = await getModels()

  return <div>{/* render models */}</div>
}

3. Handling Dynamic Content

For runtime-dependent data (cookies, headers, searchParams):

import { Suspense } from 'react'

export default function Page() {
  return (
    <>
      <h1>Static Content</h1>
      <Suspense fallback={<Skeleton />}>
        <DynamicUserContent />
      </Suspense>
    </>
  )
}

async function DynamicUserContent() {
  const session = await getSession() // uses cookies()
  return <div>{session.user.name}</div>
}

Caching Configuration

Cache Life Profiles

Use built-in lifetime profiles with cacheLife():

Default Choice: Use 'hours' for most content unless you have specific requirements.

Cache Tags and Revalidation

Using cacheTag for Manual Invalidation

Tag cached data that needs to be invalidated on specific events:

import { cacheLife, cacheTag } from 'next/cache'
import { getModelById } from '@/lib/actions/models'

export default async function ModelPage({ params }: { params: { id: string } }) {
  'use cache'
  cacheLife('hours')
  cacheTag('models', `model-${params.id}`)

  const model = await getModelById(params.id)
  return <div>{/* render model */}</div>
}

Invalidating Cache with updateTag

Use in server actions for immediate cache expiration (read-your-own-writes):

'use server'
import { updateTag } from 'next/cache'

export async function updateModel(id: string, data: ModelData) {
  // Update database via action
  await updateModelAction(id, data)

  // Immediately expire cache so user sees fresh data
  updateTag(`model-${id}`, 'models')
}

Using revalidateTag for Background Refresh

For stale-while-revalidate pattern:

'use server'
import { revalidateTag } from 'next/cache'

export async function createModel(data: ModelData) {
  await createModelAction(data)

  // Stale-while-revalidate: serve stale, refresh in background
  revalidateTag('models', 'max')
}

Best Practices

Caching Strategy

• Cache pages/layouts, not actions - Add use cache directive in pages/layouts that consume actions, never in action files themselves
• Wrap actions in cached functions - The page/layout function itself becomes the caching boundary
• Use Suspense boundaries - Separate static shell from dynamic/streaming content
• Tag strategically - Use cache tags for content that changes infrequently but needs manual updates

Performance Optimization

• Minimize dynamic APIs - Avoid using cookies(), headers(), or searchParams in cached functions
• Parallel data fetching - Multiple server actions can be called in parallel within a cached component
• Appropriate cache lifetimes - Balance freshness needs with server load

Data Mutation Patterns

• Use updateTag for user mutations - When users need to see their changes immediately
• Use revalidateTag for background updates - When serving slightly stale data is acceptable
• Tag hierarchies - Use multiple tags (e.g., 'models' and 'model-123') for flexible invalidation

Common Patterns

Pattern 1: Cached List Page

import { cacheLife, cacheTag } from 'next/cache'
import { getModels } from '@/lib/actions/models'

export default async function ModelsPage() {
  'use cache'
  cacheLife('hours')
  cacheTag('models')

  const models = await getModels()
  return <div>{/* render list */}</div>
}

Pattern 2: Cached Detail Page with Params

import { cacheLife, cacheTag } from 'next/cache'
import { getModelById } from '@/lib/actions/models'

export default async function ModelPage({ params }: { params: { id: string } }) {
  'use cache'
  cacheLife('hours')
  cacheTag('models', `model-${params.id}`)

  const model = await getModelById(params.id)
  return <div>{/* render detail */}</div>
}

Pattern 3: Mixed Static and Dynamic Content

import { Suspense } from 'react'
import { cacheLife } from 'next/cache'

export default function Page() {
  return (
    <>
      <StaticContent />
      <Suspense fallback={<LoadingSkeleton />}>
        <DynamicContent />
      </Suspense>
    </>
  )
}

async function StaticContent() {
  'use cache'
  cacheLife('hours')

  const data = await getStaticData()
  return <div>{/* render */}</div>
}

async function DynamicContent() {
  const session = await getSession() // uses cookies
  const userData = await getUserData(session.userId)
  return <div>{/* render */}</div>
}

Pattern 4: Server Action with Cache Invalidation

'use server'
import { updateTag } from 'next/cache'
import { updateModelAction } from '@/lib/actions/models'

export async function updateModel(id: string, data: FormData) {
  const result = await updateModelAction(id, data)

  if (result.status === 'success') {
    // Immediately expire cache for this specific model and all models
    updateTag(`model-${id}`, 'models')
  }

  return result
}

Important Constraints

Serialization Requirements

• Arguments must be serializable - Pass primitives, plain objects, and arrays only
• No class instances or functions - Cannot pass non-serializable values as arguments to cached functions
• Unserializable return values are OK - Can return React components or other unserializable values if you don't introspect them

What NOT to Cache

• Functions using runtime APIs - cookies(), headers(), searchParams should not be in cached functions
• Server Actions - Never add use cache to server action files; cache at the consumption point
• Highly personalized content - User-specific data that varies per request

Configuration

Enable Cache Components in next.config.ts:

const nextConfig = {
  cacheComponents: true,
}

export default nextConfig

Troubleshooting

Cache Not Working

• Verify cacheComponents: true is set in next.config.ts
• Check that use cache is at the top of the function body
• Ensure you're using Node.js runtime (Edge Runtime not supported)
• Verify function arguments are serializable

Stale Data Issues

• Check cache lifetime profile - may need shorter duration
• Use updateTag instead of revalidateTag for immediate updates
• Verify cache tags match between caching and invalidation

Performance Issues

• Profile which content needs to be cached vs. dynamic
• Use more Suspense boundaries to improve streaming
• Consider longer cache lifetimes for stable content
• Review database query performance in server actions