如何检测现有数据库的 PouchDB IndexedDB 适配器

Question

我有一个使用“idb”适配器的现有用户群。 对于新用户，我想使用“indexeddb”适配器创建数据库。 我需要找到一种方法来确定现有数据库使用的适配器，因为它可能是这两个中的任何一个。

Answer 1

要查找现有 PouchDB 数据库的当前适配器，您需要使用本机 IndexedDB API。 直接使用 PouchDB 是行不通的，因为它在数据库不存在时会创建数据库，当它是另一个版本时会失败。

下面的代码应该是诀窍（TypeScript）。

async function getCurrentAdapterForDb(dbname: string): Promise<string> {
  return new Promise<undefined | "idb" | "indexeddb">((resolve, reject) => {
    // To detect whether the database is using idb or indexeddb, we look at the version property of the indexeddb
    // If the database does not exists ==> onupgradeneeded is called with oldVersion = 0 (requesting version 1)
    // If the database exists, a version below Math.pow(10, 13) is considered idb. A version above is considered indexeddb.
    let request = window.indexedDB.open(`_pouch_${dbname}`);
    request.onupgradeneeded = function (e: IDBVersionChangeEvent): void {
      // Since no version has been requested, this mean the database do not exists.
      if (e.oldVersion === 0) {
        resolve(undefined); // Database does not exists
      }

      // We do not want the database to be created or migrated here, this is only a check. Therefore, abort the transaction.
      request.transaction.abort();
    };

    request.onerror = function (err: Event): void {
      if (request.error.code !== request.error.ABORT_ERR) {
        // Abort Error has been triggered above. Ignoring since we already resolved the promise.
        reject(request.error);
      }
    };

    request.onsuccess = function (): void {
      // When the database is successfully opened, we detect the adapter using the version
      // If we are dealing with a new database, oldVersion will be 0.
      // If we are dealing with an existing database, oldVersion will be less than indexedDbStartVersion.
      // indexedDbStartVersion is taken from pouchdb-adapter-indexeddb/index.es.js -- v7.2.2
      let indexedDbStartVersion = Math.pow(10, 13);

      if (request.result.version < indexedDbStartVersion) {
        resolve("idb");
      } else {
        resolve("indexeddb");
      }

      // Closes the database
      request.result.close();
    };
  })
}

Answer 2

请同时在浏览器中查看 PouchDB ：

console.log(yourPouchDBinstance.adapter);