サーバー状態の管理
SWRやReact Queryなどを含め、サーバーから取得したデータを管理し、UIと同期させ続けるための戦略を学びます
「サーバー状態の管理」はCoddyKit上の無料Next.js 15 Fullstack (App Router + Server Actions)レッスンです。 これはレッスン3/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはNext.js 15 Fullstack (App Router + Server Actions)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Next.js 15 Fullstack (App Router + Server Actions)コースには全4レッスンが含まれています。
このレッスンの一部はまだ翻訳されておらず、英語で表示されています。
What is Server State?
When building applications, you deal with different kinds of data. Server state refers to data that lives on a remote server, like a list of products, user profiles, or blog posts.
It's distinct from client state, which is data managed purely within your application, such as whether a modal is open or a theme is dark/light.
Challenges of Server State
Managing server state can be tricky because:
- It's Asynchronous: Data isn't instantly available; it takes time to fetch.
- It Can Be Stale: The data on the server might change after you've fetched it.
- Caching is Hard: How do you store fetched data efficiently and know when to refetch?
- Error Handling: Network requests can fail, requiring robust error management.
- Loading States: Users need feedback while data is being fetched.
Introducing SWR & React Query
Libraries like SWR (Stale-While-Revalidate) and React Query (now TanStack Query) are designed specifically to tackle these server state challenges in React applications.
They provide powerful hooks that simplify data fetching, caching, revalidation, and error handling, making your UI more robust and responsive.
Simple Asynchronous Fetch
Before using a library like SWR, fetching data asynchronously often involves manual handling of loading, success, and error states. Here's a basic JavaScript example:
async function fetchData() {
console.log("Fetching data...");
try {
const response = await fetch('https://jsonplaceholder.typicode.com/todos/1');
if (!response.ok) {
throw new Error(`HTTP error! status: ${response.status}`);
}
const data = await response.json();
console.log("Data fetched: ", data.title);
} catch (error) {
console.error("Fetch error: ", error.message);
}
}
fetchData();The useSWR Hook
SWR wraps this fetching logic into a convenient React Hook called useSWR. It automatically provides the data, error, and a loading state (implicitly via data being undefined initially).
You provide a unique key (often the API endpoint) and a fetcher function that makes the actual data request.
import useSWR from 'swr';
const fetcher = url => fetch(url).then(res => res.json());
function UserProfile() {
// The key is '/api/user', the fetcher is our function
const { data, error } = useSWR('/api/user', fetcher);
if (error) return <div>Failed to load user.</div>;
if (!data) return <div>Loading user...</div>;
return <div>Hello, {data.name}!</div>;
}
// In a Next.js app, UserProfile would be rendered
// inside a page component.Smart Caching & Deduping
One of SWR's core features is its intelligent caching. When multiple components request data with the same key, SWR automatically deduplicates these requests, fetching the data only once.
It then shares this cached data across all subscribers, preventing unnecessary network calls and improving performance. This is crucial for large applications.
Stale-While-Revalidate Strategy
SWR's name comes from its Stale-While-Revalidate caching strategy. This means:
- It immediately returns the cached (stale) data to the UI.
- It then sends a request to revalidate (fetch new) data in the background.
- Once new data arrives, it updates the UI.
This provides an instant user experience while ensuring data freshness.
Automatic Revalidation
SWR and React Query automatically revalidate data in several common scenarios, ensuring your UI always reflects the latest server state:
- On Focus: When the browser tab or window regains focus.
- On Reconnect: When the network connection is restored.
- On Interval: You can configure periodic revalidation for frequently changing data.
This significantly reduces the need for manual data refreshing.
Mutating Data & UI Updates
When you perform actions that change server data (e.g., submitting a form to create a new post), you need to update your UI. SWR provides a mutate function to help with this.
You can use mutate to manually revalidate the data associated with a key, or even update the local cache directly for immediate optimistic UI updates.
Server State Check
Which of the following are key benefits of using a library like SWR or React Query for managing server state?
Recap & Next Steps
You've explored the world of server state and learned why it requires special handling compared to client state. Libraries like SWR and React Query are indispensable tools for Next.js developers, simplifying data fetching, caching, revalidation, and error management.
By leveraging these libraries, you can build more performant, reliable, and user-friendly applications with less effort. Keep practicing these concepts to master your data fetching!
よくある質問
「サーバー状態の管理」レッスンは無料ですか？
はい。「サーバー状態の管理」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Next.js 15 Fullstack (App Router + Server Actions)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Next.js 15 Fullstack (App Router + Server Actions)コースには全4レッスンが含まれています。
「サーバー状態の管理」で何を学びますか？
SWRやReact Queryなどを含め、サーバーから取得したデータを管理し、UIと同期させ続けるための戦略を学びます ブラウザで直接実行するハンズオンコードでNext.js 15 Fullstack (App Router + Server Actions)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。
Next.js 15 Fullstack (App Router + Server Actions)を始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのNext.js 15 Fullstack (App Router + Server Actions)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン3/4です。
「サーバー状態の管理」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このNext.js 15 Fullstack (App Router + Server Actions)レッスンでコードを書いて実行できますか？
はい。すべてのNext.js 15 Fullstack (App Router + Server Actions)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。