javascript - IndexedDB - 如何读取对象存储中的最大 ID

Question

我正在开发一个从服务器读取数据的网络应用程序，为了节省成本，需要将数据存储在浏览器上，以便它可以“增量”从服务器读取数据而不是全部读取每次，以减少网络使用。

我目前拥有的是:

• 将数组添加到现有对象存储的函数:

function IXDBaddItems(osName, items, callback) {
  const tx = db.transaction([osName], "readwrite");
  const obj = tx.objectStore(osName);

  items.forEach(item => {
    obj.put(item);
  })

  tx.oncomplete = (event) => {
    callback();
  }
};

• 一个函数，它在服务器上使用参数“lastId”进行增量 ajax 调用，并最终将结果存储在 objectStore 中

const getCorsiLastId = (lastId) => {
  makeAjaxCall(urlCorsiVendite, "POST", {
      ultimoId: lastId
    })
    .then(
      (resp) => {
        resp.forEach(d => {
          d.id = +d.id;
          d.id_course = +d.id_course;
          d.id_user = +d.id_user;
          d.insert_Date = new Date(d.insert_Date);
          d.nome_corso = d.nome_corso;
          d.year = +d.insert_Date.getFullYear();
          d.month = +d.insert_Date.getMonth() + 1;
          d.ref = +d.ref;
        });
      IXDBaddItems('corsiVendite', resp, () => console.log('db corsi update completed'));
      },
      (err) => console.log(err)
    );
};

• “异步主体”:

let db;

(async () => {
  let request = window.indexedDB.open('dbKpiMarketing', 1);

  // onerror handler signifies that the database didn't open successfully
  request.onerror = (e) => {
    console.log(e);
  };

  // onsuccess handler signifies that the database opened successfully
  request.onsuccess = async(e) => {
    console.log('Database opened successfully');

    // Store the opened database object in the db variable. This is used a lot below
    db = request.result;

    getCorsiLastId(0);
  };

  // Setup the database tables if this has not already been done
  request.onupgradeneeded = (e) => {
    // Grab a reference to the opened database
    let db = e.target.result;

    // Create an objectStore to store our data
    let osCorsi = db.createObjectStore('corsiVendite', {
      keyPath: 'id'
    });
    let osServizi = db.createObjectStore('serviziVendite', {
      keyPath: 'id'
    });

    console.log('Database setup complete');
  };

})();

现在我正在使用 lastId=0 调用 ajax 函数以取回所有内容。我需要让它充满活力。通过控制台中的这两行代码，我得到了我要找的东西:最高存储 ID。

let c = db.transaction('corsiVendite').objectStore('corsiVendite').getAll()
let lastIdCorsi = Math.max(...c.result.map(d=>d.id));

我需要在调用 getCorsiLastId(LastIdCorsi) 之前获取这两行并运行它们，但如果我尝试这样做，我会收到错误消息:Uncaught (in promise) DOMException: Failed to read the “IDBRequest”的“结果”属性:请求尚未完成。我知道交易需要一些时间，所以我不能立即使用结果。我该如何克服这个问题？

Answer 1

我想我已经解决了...我实际上已经在 IXDBaddItems 函数中使用事务的 oncomplete 方法做了正确的事情。我添加了这些行:

let t = db.transaction('corsiVendite', 'readwrite');
let o = t.objectStore('corsiVendite');
let c = o.getAll();
t.oncomplete = (e) => {
    LastId = Math.max(...c.result.map(d=>d.id));
};