/nextjs-data-fetching

name: nextjs-data-fetching
description: Provides Next.js App Router data fetching patterns including SWR and React Query integration, parallel data fetching, Incremental Static Regeneration (ISR), revalidation strategies, and error boundaries. Use when implementing data fetching in Next.js applications, choosing between server and client fetching, setting up caching strategies, or handling loading and error states.
allowed-tools: Read, Write, Edit, Bash

Next.js Data Fetching

Overview

Provides patterns for data fetching in Next.js App Router: server-side fetching, SWR/React Query integration, ISR, revalidation, error boundaries, and loading states.

When to Use

• Implementing data fetching in Next.js App Router
• Choosing between Server Components and Client Components
• Setting up SWR or React Query for client-side caching
• Configuring ISR, time-based, or on-demand revalidation
• Handling loading and error states
• Building forms with Server Actions

Instructions

Server Component Fetching

Fetch directly in async Server Components:

async function getPosts() {
  const res = await fetch('https://api.example.com/posts');
  if (!res.ok) throw new Error('Failed to fetch posts');
  return res.json();
}

export default async function PostsPage() {
  const posts = await getPosts();
  return (
    <ul>
      {posts.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  );
}

Parallel Data Fetching

Use `Promise.all()` for independent requests:

async function getDashboardData() {
  const [user, posts, analytics] = await Promise.all([
    fetch('/api/user').then(r => r.json()),
    fetch('/api/posts').then(r => r.json()),
    fetch('/api/analytics').then(r => r.json()),
  ]);
  return { user, posts, analytics };
}

export default async function DashboardPage() {
  const { user, posts, analytics } = await getDashboardData();
  // Render dashboard
}

Sequential Data Fetching (When Dependencies Exist)

async function getUserPosts(userId: string) {
  const user = await fetch(`/api/users/${userId}`).then(r => r.json());
  const posts = await fetch(`/api/users/${userId}/posts`).then(r => r.json());
  return { user, posts };
}

Time-based Revalidation (ISR)

async function getPosts() {
  const res = await fetch('https://api.example.com/posts', {
    next: { revalidate: 60 } // Revalidate every 60 seconds
  });
  return res.json();
}

On-Demand Revalidation

// app/api/revalidate/route.ts
import { revalidateTag } from 'next/cache';
import { NextRequest } from 'next/server';

export async function POST(request: NextRequest) {
  const tag = request.nextUrl.searchParams.get('tag');
  if (tag) {
    revalidateTag(tag);
    return Response.json({ revalidated: true });
  }
  return Response.json({ revalidated: false }, { status: 400 });
}

Tag data for selective revalidation:

async function getPosts() {
  const res = await fetch('https://api.example.com/posts', {
    next: { tags: ['posts'], revalidate: 3600 }
  });
  return res.json();
}

Opt-out of Caching

async function getRealTimeData() {
  const res = await fetch('https://api.example.com/data', {
    cache: 'no-store'
  });
  return res.json();
}

// Or:
export const dynamic = 'force-dynamic';

Client-Side Data Fetching

SWR Integration

Install: `npm install swr`

'use client';

import useSWR from 'swr';

const fetcher = (url: string) => fetch(url).then(r => r.json());

export function Posts() {
  const { data, error, isLoading } = useSWR('/api/posts', fetcher, {
    refreshInterval: 5000,
    revalidateOnFocus: true,
  });

  if (isLoading) return <div>Loading...</div>;
  if (error) return <div>Failed to load posts</div>;

  return (
    <ul>
      {data.map((post: any) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  );
}

React Query Integration

Install: `npm install @tanstack/react-query`

// app/providers.tsx
'use client';

import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
import { useState } from 'react';

export function Providers({ children }: { children: React.ReactNode }) {
  const [queryClient] = useState(() => new QueryClient({
    defaultOptions: {
      queries: {
        staleTime: 60 * 1000,
        refetchOnWindowFocus: false,
      },
    },
  }));

  return (
    <QueryClientProvider client={queryClient}>
      {children}
    </QueryClientProvider>
  );
}

See [react-query.md](references/react-query.md) for mutations, optimistic updates, infinite queries, and advanced patterns.

Error Boundaries

Wrap client-side data fetching in Error Boundaries to handle failures gracefully:

See [error-boundaries.md](references/error-boundaries.md) for full `ErrorBoundary` implementations (basic, with reset callback) and usage examples with data fetching.

Server Actions

Use Server Actions for mutations with cache revalidation:

See [server-actions.md](references/server-actions.md) for complete examples including form validation with `useActionState`, error handling, and cache invalidation.

Loading States

loading.tsx Pattern

// app/posts/loading.tsx
export default function PostsLoading() {
  return (
    <div className="space-y-4">
      {[...Array(5)].map((_, i) => (
        <div key={i} className="h-16 bg-gray-200 animate-pulse rounded" />
      ))}
    </div>
  );
}

Suspense Boundaries

// app/posts/page.tsx
import { Suspense } from 'react';
import { PostsList } from './PostsList';
import { PostsSkeleton } from './PostsSkeleton';

export default function PostsPage() {
  return (
    <div>
      <h1>Posts</h1>
      <Suspense fallback={<PostsSkeleton />}>
        <PostsList />
      </Suspense>
    </div>
  );
}

Best Practices

1. **Default to Server Components** — Fetch in Server Components for better performance 2. **Use parallel fetching** — `Promise.all()` for indep