Question

我正在创建indexedDB数据库products_db。

onload将objectStore products_os添加到数据库。
从服务器获取数据并将数据添加到products_os。
在UI中显示数据。

add

onclick，尝试打开具有更高版本号的数据库并创建一个新的objectStore cart_os。 这是无法正常工作的地方。

当前行为：

当我以隐身模式打开chrome浏览器并将 index.html 文件加载到选项卡中时，UI中会显示一个表格行，但是{{ 1}}在Application中没有Developer Tools数据库中。
点击添加按钮后，系统会显示product_db事件的警报弹出indexedDB。（没有其他选项卡打开此站点！）。关闭弹出窗口后，现在单击同一添加按钮无济于事。
现在，如果我使用 cmd + shift + r 刷新页面，则会在表中添加新行。现在总共有两行。每次刷新时，都会添加新行。上一点对于UI中的所有添加按钮都是正确的，单击任何一个按钮都会触发警报，然后所有按钮都变得无用。（不会弹出onclick）。
如果我清除存储空间，然后执行 cmd + shift + r ，那么在UI中，我只会得到一行。

预期行为：

开发人员工具

应用

indexedDB不应为空。相反，应使用onblocked和function addCartData(e) {填充它。
在刷新时，如果不清除存储，则只应一行每次显示。
db（添加按钮），将打开一个具有新版本号的数据库，并向其添加objectStore objectStore。这样以后我就可以将onclick用于cart_os交易了。

index.html

cart_os

script.js

read/write

styles.css

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Product Table</title>
    <link href="styles.css" rel="stylesheet">
    <script src="script.js" defer></script>
  </head>
  <body>
    <table id='idb-table' style="width=100%" />
  </body>
</html>

product.json

// Create an instance of a db object for us to store the open database in
let db;

window.onload = function() {
  // Open our database; it is created if it doesn't already exist
  let request = window.indexedDB.open('products_db', 1);

  // onerror handler signifies that the database didn't open successfully
  request.onerror = function() {
    console.log('Database failed to open');
  }

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

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

    // Run the fetchProducts() function to fetch data from external API 
    fetchProducts();
  }

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

    // Create an objectStore to store our products in (basically like a single table)
    // including a auto-incrementing key
    let objectStore = db.createObjectStore('products_os', {keyPath: 'id', autoIncrement: true});

    // Define what data items the objectStore will contain
    objectStore.createIndex('title', 'title', {unique: false});
    objectStore.createIndex('price', 'price', {unique: false});
    objectStore.createIndex('inStock', 'inStock', {unique: false});

  }

  function fetchProducts() {
    let product1 = fetch('http://localhost:3001/location/pathname') // see product.json file
      .then(function(response) {
        return response.json();
      })
      .then(function(response) {
        addData(response);
      })
  }

  function addData(value) {
    // open a read/write db transaction, ready for adding the data
    let transaction = db.transaction(['products_os'], 'readwrite');

    // call an object store that's already been added to the database
    let objectStore = transaction.objectStore('products_os');

    let newItem = {
      title: value.title,
      price: value.sellingPrice,
      inStock: value.inStock,
    };

    // Make a request to add our newItem object to the object store
    var request = objectStore.add(newItem);

    transaction.oncomplete = function() {
      console.log('Transaction completed: database modification finished.');

      // update the display of data to show the newly added item, by running displayData() again.
      displayData();
    }

    transaction.onerror = function() {
      console.log('Transaction not opened due to error');
    };
  }

  function displayData() {
    // Open our object store and then get a cursor - which iterates through all the
    // different data items in the store
    let objectStore = db.transaction('products_os').objectStore('products_os');

    objectStore.openCursor().onsuccess = function(e) {
      // Get a reference to the cursor
      let cursor = e.target.result;

      // Get a reference to table
      let table = document.querySelector('#idb-table');

      // If there is still another data item to iterate through, keep running this code
      if(cursor) {
        // Insert into table,
        // structure the HTML fragment, and append it inside the table
        let tableRow = document.createElement('tr');
        for (let val in cursor.value) {
          if (Object.prototype.hasOwnProperty.call(cursor.value, val)) {
            if (val !== 'id') {
              let td = document.createElement('td');
              tableRow.appendChild(td);
              td.textContent = cursor.value[val];
            }
          }
        }
        let td = document.createElement('td');
        td.setAttribute('align', 'center');
        let addButton = document.createElement('button');
        td.appendChild(addButton);
        addButton.textContent = 'Add';
        addButton.addEventListener('click', function(e) {
          addCartData(e);
        })
        tableRow.appendChild(td);
        table.appendChild(tableRow);

        // Iterate to the next item in the cursor
        cursor.continue();
      }
    }
  }

  function addCartData(e) {
    // Open the db with higher version number
    let req = window.indexedDB.open('products_db', 2);

    req.onerror = function() {
      console.log('Database failed to open');
    }

    req.onsuccess = function() {
      console.log('Database opened successfully');

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

    req.onblocked = function(event) {
      // If some other tab is loaded with the database, then it needs to be closed
      // before we can proceed.
      alert("Please close all other tabs with this site open!");
    };

    req.onupgradeneeded = function(e){
      // Grab a reference to the opened database
      let db = e.target.result;

      // Create a cart objectStore to store our information added to the cart
      let cartStore = db.createObjectStore('cart_os', {keyPath: 'id', autoIncrement: true});

      // Define what data items the cart objectStore will contain
      cartStore.createIndex('title', 'title', {unique: false});
      cartStore.createIndex('price', 'price', {unique: false});
    }
  }

编辑

objectStore products_os was never added to db

如图所示，在 207 行出现错误table { font-family: arial, sans-serif; border-collapse: collapse; width: 100%; } td, th { border: 1px solid #dddddd; text-align: left; padding: 8px; } tr:nth-child(even) { background-color: #dddddd; } tr:last-child { text-align: center!important; }。

onupgradeneeded_version1：

{
   "title": "Newhide Designer",
   "productDescription": "",
   "sellingPrice": 119,
   "inStock": true,
}

Answer 1

嗯，对于如何改进此代码，我有很多建议，但要直截了当，我认为问题出在以下事实：首先打开数据库连接并保持打开状态（无限期）），然后在您的点击处理程序中，打开具有更高版本号的第二个数据库版本，如果单击该版本，则会在初始数据库连接仍处于打开状态时发生。

我建议将indexedDB.open => db逻辑封装在promise中。这将使代码更易于读写。然后，我建议更改您使用该承诺的方式。

这是我的想法：

function open(name, version, onupgradeneeded) {
  return new Promise(function executor(resolve, reject) {
    const request = indexeDB.open(name, version);
    request.onsuccess = function(event) { resolve(request.result); };
    request.onerror = function(event) { reject(request.result); };
    request.onblocked = function(event) { console.debug('blocked indefinitely'); };
    request.onupgradeneeded = onupgradeneeded;
  });
}

async function fetch_product() {
  const response = await fetch('http://localhost:3001/location/pathname');
  const data = await response.json();
  return data;
}

function add_product(db, data) {
  return new Promise(function(resolve, reject) {
    const transaction = db.transaction(..., 'readwrite');
    transaction.oncomplete = resolve;
    transaction.onerror = reject;
    const store = transaction.objectStore(...);
    store.put(data);
  });
}

function get_products(db) {
  return new Promise(function(resolve, reject) {
    const transaction = db.transaction(...);
    const store = transaction.objectStore(...);
    const request = store.getAll();
    request.onsuccess = function(event) {
      const products_array = request.result;
      resolve(products_array);
    };
    request.onerror = function(event) {
      reject(request.error);
    };
  });
}

function render_product(product) {
  const table = document.getElementById('table-id');

  // create rows and all that.
  // and append
  button.onclick = handle_click;
}

async function handle_click(event) {

  // Based on what was clicked, find and build the product data object
  // event.target is the button
  const row = event.target.closest('tr');
  const name = row.querySelector('td.namecolumn').textContent;
  // etc
  const product = {
    name: name
  };

  const db = await open(name, version2, onupgradeneeded_for_version2);
  await add_product(db, product);
  db.close();
}

async function onload() {
  const product = await fetch_product();
  const db = await open(name, version, onupgradeneeded_version1);
  await add_product(db, product);

  const products = await get_products(db);

  // we are done with the db now
  db.close();

  // print out product data
  for(const product of products) {
    render_product(product);
  }  
}

尝试打开具有更高版本号的数据库时触发了onblocked

1 个答案: