Membina asas panduan ini untuk mencipta cache dalam memori, kami akan meneruskannya dengan memperkenalkan kekekalan data boleh dikonfigurasikan. Dengan memanfaatkan corak Penyesuai dan Strategi, kami akan mereka bentuk sistem yang boleh diperluaskan yang memisahkan mekanisme storan daripada logik caching, membenarkan penyepaduan pangkalan data atau perkhidmatan yang lancar mengikut keperluan.

Visi: Menyahganding Seperti ORM

Matlamatnya adalah untuk menjadikan cache boleh dipanjangkan tanpa mengubah logik terasnya. Diilhamkan oleh sistem ORM, pendekatan kami melibatkan abstraksi API dikongsi. Ini membolehkan storan — seperti localStorage, IndexedDB atau pangkalan data jauh—berfungsi secara bergantian dengan perubahan kod yang minimum.

Kelas Asas Penyesuai Storan

Berikut ialah kelas abstrak yang mentakrifkan API untuk sebarang sistem kegigihan:

export abstract class StorageAdapter {
  abstract connect(): Promise<void>;
  abstract add(key: string, value: unknown): Promise<void>;
  abstract get(key: string): Promise<unknown | null>;
  abstract getAll(): Promise<Record<string, unknown>>;
  abstract delete(key: string): Promise<void>;
  abstract clear(): Promise<void>;
}

Sebarang penyelesaian storan mesti memanjangkan kelas asas ini, memastikan konsistensi dalam interaksi. Sebagai contoh, berikut ialah pelaksanaan untuk IndexedDB:

Contoh: Penyesuai IndexedDB

Penyesuai ini melaksanakan antara muka StorageAdapter untuk mengekalkan data cache dalam gedung IndexedDB.

import { StorageAdapter } from './storage_adapter';

/**
 * IndexedDBAdapter is an implementation of the StorageAdapter 
 * interface designed to provide a persistent storage mechanism 
 * using IndexedDB. This adapter can be reused for other cache 
 * implementations or extended for similar use cases, ensuring 
 * flexibility and scalability.
 */
export class IndexedDBAdapter extends StorageAdapter {
  private readonly dbName: string;
  private readonly storeName: string;
  private db: IDBDatabase | null = null;

  /**
   * Initializes the adapter with the specified database and store 
   * names. Defaults are provided to make it easy to set up without 
   * additional configuration.
   */
  constructor(dbName: string = 'cacheDB', storeName: string = 'cacheStore') {
    super();
    this.dbName = dbName;
    this.storeName = storeName;
  }

  /**
   * Connects to the IndexedDB database and initializes it if 
   * necessary. This asynchronous method ensures that the database 
   * and object store are available before any other operations. 
   * It uses the `onupgradeneeded` event to handle schema creation 
   * or updates, making it a robust solution for versioning.
   */
  async connect(): Promise<void> {
    return await new Promise((resolve, reject) => {
      const request = indexedDB.open(this.dbName, 1);

      request.onupgradeneeded = (event) => {
        const db = (event.target as IDBOpenDBRequest).result;
        if (!db.objectStoreNames.contains(this.storeName)) {
          db.createObjectStore(this.storeName, { keyPath: 'key' });
        }
      };

      request.onsuccess = (event) => {
        this.db = (event.target as IDBOpenDBRequest).result;
        resolve();
      };

      request.onerror = () => reject(request.error);
    });
  }

  /**
   * Adds or updates a key-value pair in the store. This method is 
   * asynchronous to ensure compatibility with the non-blocking 
   * nature of IndexedDB and to prevent UI thread blocking. Using 
   * the `put` method ensures idempotency: the operation will 
   * insert or replace the entry.
   */
  async add(key: string, value: unknown): Promise<void> {
    await this._withTransaction('readwrite', (store) => store.put({ key, value }));
  }

  /**
   * Retrieves the value associated with a key. If the key does not 
   * exist, null is returned. This method is designed to integrate 
   * seamlessly with caching mechanisms, enabling fast lookups.
   */
  async get(key: string): Promise<unknown | null> {
    return await this._withTransaction('readonly', (store) =>
      this._promisifyRequest(store.get(key)).then((result) =>
        result ? (result as { key: string; value: unknown }).value : null
      )
    );
  }

  /**
   * Fetches all key-value pairs from the store. Returns an object 
   * mapping keys to their values, making it suitable for bulk 
   * operations or syncing with in-memory caches.
   */
  async getAll(): Promise<Record<string, unknown>> {
    return await this._withTransaction('readonly', (store) =>
      this._promisifyRequest(store.getAll()).then((results) =>
        results.reduce((acc: Record<string, unknown>, item: { key: string; value: unknown }) => {
          acc[item.key] = item.value;
          return acc;
        }, {})
      )
    );
  }

  /**
   * Deletes a key-value pair by its key. This method is crucial 
   * for managing cache size and removing expired entries. The 
   * `readwrite` mode is used to ensure proper deletion.
   */
  async delete(key: string): Promise<void> {
    await this._withTransaction('readwrite', (store) => store.delete(key));
  }

  /**
   * Clears all entries from the store. This method is ideal for 
   * scenarios where the entire cache needs to be invalidated, such 
   * as during application updates or environment resets.
   */
  async clear(): Promise<void> {
    await this._withTransaction('readwrite', (store) => store.clear());
  }

  /**
   * Handles transactions in a reusable way. Ensures the database 
   * is connected and abstracts the transaction logic. By 
   * centralizing transaction handling, this method reduces 
   * boilerplate code and ensures consistency across all operations.
   */
  private async _withTransaction<T>(
    mode: IDBTransactionMode,
    callback: (store: IDBObjectStore) => IDBRequest | Promise<T>
  ): Promise<T> {
    if (!this.db) throw new Error('IndexedDB is not connected');
    const transaction = this.db.transaction([this.storeName], mode);
    const store = transaction.objectStore(this.storeName);
    const result = callback(store);
    return result instanceof IDBRequest ? await this._promisifyRequest(result) : await result;
  }

  /**
   * Converts IndexedDB request events into Promises, allowing for 
   * cleaner and more modern asynchronous handling. This is 
   * essential for making IndexedDB operations fit seamlessly into 
   * the Promise-based architecture of JavaScript applications.
   */
  private async _promisifyRequest<T>(request: IDBRequest): Promise<T> {
    return await new Promise((resolve, reject) => {
      request.onsuccess = () => resolve(request.result as T);
      request.onerror = () => reject(request.error);
    });
  }
}

Mengintegrasikan Penyesuai ke dalam Cache

Cache menerima StorageAdapter pilihan. Jika disediakan, ia memulakan sambungan pangkalan data, memuatkan data ke dalam ingatan dan memastikan cache serta storan sentiasa disegerakkan.

private constructor(capacity: number, storageAdapter?: StorageAdapter) {
  this.capacity = capacity;
  this.storageAdapter = storageAdapter;

  if (this.storageAdapter) {
    this.storageAdapter.connect().catch((error) => {
      throw new Error(error);
    });

    this.storageAdapter.getAll().then((data) => {
      for (const key in data) {
        this.put(key, data[key] as T);
      }
    }).catch((error) => {
      throw new Error(error);
    });
  }

  this.hash = new Map();
  this.head = this.tail = undefined;

  this.hitCount = this.missCount = this.evictionCount = 0;
}

Mengapa Corak Penyesuai dan Strategi?

Menggunakan corak Penyesuai:

• Decouples cache daripada mekanisme storan tertentu.
• Memastikan kebolehlanjutan untuk bahagian belakang storan baharu.

Menggabungkan dengan corak Strategi:

• Mendayakan pemilihan masa jalan lapisan kegigihan.
• Memudahkan ujian dengan mengejek penyesuai yang berbeza.

Amalan Reka Bentuk Utama

• API Abstrak: Mengekalkan logik cache agnostik butiran storan.
• Cache Singleton: Memastikan konsistensi keadaan dikongsi.
• Permulaan Async: Mengelakkan operasi menyekat semasa persediaan.
• Lazy Loading: Hanya memuatkan data berterusan apabila penyesuai storan disediakan.

Langkah Seterusnya

Reka bentuk ini teguh tetapi memberi ruang untuk penambahbaikan:

• Optimumkan logik penyegerakan untuk prestasi yang lebih baik.
• Percubaan dengan penyesuai tambahan seperti Redis atau SQLite.

Cubalah! ?

Jika anda ingin menguji cache dalam tindakan, ia tersedia sebagai pakej npm: adev-lru. Anda juga boleh menerokai kod sumber penuh pada GitHub: repositori adev-lru. Saya mengalu-alukan sebarang cadangan, maklum balas yang membina atau sumbangan untuk menjadikannya lebih baik! ?

Selamat pengekodan! ?

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