React Native Academy · Урок

Очистка хранилища и стратегии миграции

«Очистка хранилища и стратегии миграции» — бесплатный урок React Native Academy на CoddyKit. Это урок 4 из 4. Ты можешь прочитать весь урок бесплатно ниже — а потом практиковать его прямо в браузере с встроенным редактором кода и ИИ-репетитором 24/7. Это часть пути обучения React Native Academy, и твой прогресс синхронизируется между веб-версией и приложением CoddyKit. Курс React Native Academy содержит 4 уроков всего.

Части этого урока еще не переведены и отображаются на английском.

Why Storage Maintenance Matters

As your app evolves across versions, the data structure you store in AsyncStorage may change. Old data from previous app versions might not match what the new code expects, leading to crashes or incorrect behavior. A solid storage maintenance strategy — including selective clearing and versioned migrations — is essential for apps that have real users with existing data.

Removing Specific Keys with multiRemove

AsyncStorage.multiRemove accepts an array of key strings and deletes all of them in a single operation. This is more efficient than calling removeItem repeatedly in a loop. Use it when a user action should clear a specific subset of data — for example removing all cached API responses without touching user preferences.

async function clearCache() {
  const cacheKeys = [
    'posts_cache',
    'comments_cache',
    'user_feed_cache',
  ];
  try {
    await AsyncStorage.multiRemove(cacheKeys);
    console.log('Cache cleared');
  } catch (err) {
    console.error('Failed to clear cache:', err);
  }
}

Clearing All App Data with clear

AsyncStorage.clear() removes all keys stored by the app. Use this only for destructive operations like a factory reset or during development when you need a clean slate. In production, always confirm with the user before calling clear() because it cannot be undone and deletes everything — preferences, cached data, and auth tokens alike.

async function factoryReset() {
  await AsyncStorage.clear();
  // Reset in-memory state too
  useAuthStore.getState().logout();
  useSettingsStore.getState().reset();
  navigation.reset({ index: 0, routes: [{ name: 'Onboarding' }] });
}

Finding Keys to Remove Dynamically

When you store data with dynamic keys (like post_123, post_456), use getAllKeys to find them and filter by a prefix before passing the matching keys to multiRemove. This pattern is useful for clearing all cached pages from a paginated feed without hardcoding each key.

async function clearPostsCache() {
  const allKeys = await AsyncStorage.getAllKeys();
  const postKeys = allKeys.filter((key) => key.startsWith('post_'));
  if (postKeys.length > 0) {
    await AsyncStorage.multiRemove(postKeys);
    console.log('Cleared', postKeys.length, 'cached posts');
  }
}

What Is a Storage Migration?

A storage migration upgrades stored data from one schema version to a newer one. When you release a new app version that changes how data is stored — for example renaming a key or adding a required field — migrating existing users' data prevents crashes and data loss. Migrations run once on startup and mark the completion with a version flag.

Versioning Your Storage Schema

Store a schema version number in AsyncStorage alongside your data. On startup, read this version number and compare it to the current expected version. If they differ, run the appropriate migration steps, then update the stored version number. Future launches skip the migration because the versions match.

const CURRENT_VERSION = 3;
const VERSION_KEY = 'storage_version';

async function getStorageVersion(): Promise<number> {
  const v = await AsyncStorage.getItem(VERSION_KEY);
  return v ? parseInt(v, 10) : 0; // 0 means fresh install or pre-versioning
}

async function setStorageVersion(version: number) {
  await AsyncStorage.setItem(VERSION_KEY, String(version));
}

Writing a Migration Function

Write a migration function that handles each version upgrade step. Use a switch statement or a series of if checks that fall through from the stored version up to the current version. Each case applies the changes needed to advance one version, so a user upgrading from v1 to v3 runs both the v1-to-v2 and v2-to-v3 migrations in sequence.

async function runMigrations(fromVersion: number) {
  if (fromVersion < 1) {
    // v0 → v1: rename 'user_name' key to 'username'
    const old = await AsyncStorage.getItem('user_name');
    if (old) {
      await AsyncStorage.setItem('username', old);
      await AsyncStorage.removeItem('user_name');
    }
  }
  if (fromVersion < 2) {
    // v1 → v2: add default 'fontSize' to settings
    const json = await AsyncStorage.getItem('settings');
    if (json) {
      const settings = JSON.parse(json);
      if (!settings.fontSize) settings.fontSize = 'medium';
      await AsyncStorage.setItem('settings', JSON.stringify(settings));
    }
  }
  await setStorageVersion(CURRENT_VERSION);
}

Running Migrations on App Start

Call the migration logic in your root component's useEffect before anything else reads from storage. This ensures all data is in the expected shape before any screen tries to use it. Keep migrations idempotent — running them twice on the same data should produce the same result to handle edge cases like interrupted writes.

useEffect(() => {
  async function init() {
    const version = await getStorageVersion();
    if (version < CURRENT_VERSION) {
      await runMigrations(version);
    }
    // Now safe to load data — migration is complete
    await loadAppData();
    setAppReady(true);
  }
  init();
}, []);

Expiring Cached Data

Cache data should not live forever. Store a timestamp alongside cached API responses and check whether it has expired when the app starts or when the user navigates to a screen. If expired, delete the cache and fetch fresh data. A helper function that wraps the cache check makes this reusable across all cached endpoints.

const CACHE_TTL_MS = 60 * 60 * 1000; // 1 hour

async function isCacheExpired(key: string): Promise<boolean> {
  const tsStr = await AsyncStorage.getItem(key + '_timestamp');
  if (!tsStr) return true;
  return Date.now() - parseInt(tsStr, 10) > CACHE_TTL_MS;
}

async function setCache(key: string, data: any) {
  await AsyncStorage.setItem(key, JSON.stringify(data));
  await AsyncStorage.setItem(key + '_timestamp', String(Date.now()));
}

Selective Logout: Clearing Only User Data

When a user logs out, clear their personal data (auth token, profile, private cache) but preserve device preferences like theme and language. Use multiRemove with a specific list of keys rather than clear(). This provides a better UX because the user's display preferences are still there when they log back in.

const USER_DATA_KEYS = ['authToken', 'userProfile', 'feed_cache', 'userId'];

async function logout() {
  await AsyncStorage.multiRemove(USER_DATA_KEYS);
  // Preferences (theme, language) remain intact
  navigation.reset({ index: 0, routes: [{ name: 'Login' }] });
}

Documenting Your Storage Schema

Maintain a storage schema documentation file in your project that lists every AsyncStorage key, its type, its default value, and which version it was introduced. This is invaluable when writing migrations, debugging storage issues, and onboarding new developers. Treat it like a database schema — update it every time you add, rename, or remove a stored key.

/**
 * AsyncStorage Schema v3
 * -------------------------
 * Key              | Type    | Since | Description
 * authToken        | string  | v1    | JWT auth token
 * username         | string  | v1    | (was user_name in v0)
 * settings         | JSON    | v1    | { darkMode, notifications, fontSize }
 *   .fontSize added v2, .language added v3
 * storage_version  | number  | v1    | Current schema version
 */

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: multiRemove efficiently clears a specific set of keys while leaving others intact, versioned migrations upgrade old stored data when the app schema changes across releases, and expiring cached data with timestamps prevents stale API responses from living in storage indefinitely. Next up we explore camera access with expo-camera.

Часто задаваемые вопросы

Урок «Очистка хранилища и стратегии миграции» бесплатный?

Да — полный текст урока «Очистка хранилища и стратегии миграции» бесплатно доступен здесь в веб-версии. Чтобы практиковать его интерактивно (встроенный редактор кода и ИИ-репетитор 24/7) и разблокировать остальной курс React Native Academy, подпишись на CoddyKit PRO. Курс React Native Academy содержит 4 уроков всего.

Чему я научусь в уроке «Очистка хранилища и стратегии миграции»?

Используйте multiRemove и clear для выборочной и полной очистки кэша и реализуйте версионируемую стратегию миграции для обработки изменений схемы хранилища между обновлениями приложения. Ты практикуешь React Native Academy с помощью реального кода, который запускаешь прямо в браузере, и ИИ-репетитор 24/7 отвечает на твои вопросы во время урока.

Нужен ли мне опыт, чтобы начать React Native Academy?

Предыдущий опыт не требуется. React Native Academy на CoddyKit структурирован для всех уровней — от новичков до продвинутых, поэтому ты можешь начать отсюда или с самого начала и учиться в своем темпе. Это урок 4 из 4.

Сколько времени занимает урок «Очистка хранилища и стратегии миграции»?

Большинство уроков CoddyKit занимают около 5–10 минут. Каждый из них компактный и интерактивный, поэтому ты постоянно делаешь прогресс и продолжаешь с того же места в веб-версии и приложении.

Можно ли писать и запускать код в этом уроке React Native Academy?

Да. Каждый урок React Native Academy включает встроенный редактор кода, поэтому ты пишешь и запускаешь реальный код прямо в браузере и получаешь моментальную обратную связь от AI — локальная установка не требуется.

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