无法读取未定义IndexedDB的属性“事务”

Question

我使用IndexDB来创建用户的对象存储，但是当试图添加用户时，我在var request = db.transaction(['person'], 'readwrite')行上得到了一个错误。

给出的错误是：

“未定义的TypeError:无法读取未定义的属性‘在test.js:45的添加(test.js:32)’”

我的剧本是这样的：

var request = window.indexedDB.open("connectDB", 1);

request.onerror = function (event) 
{
console.log('The database is opened failed');
};

var db;

request.onsuccess = function (event) 
{
    db = request.result;
console.log('The database is opened successfully');
};

var db;

request.onupgradeneeded = function (event) 
{
    db = event.target.result;
    var objectStore;
    if (!db.objectStoreNames.contains('users'))
    {
        objectStore = db.createObjectStore('users', { keyPath: 'id' });
        objectStore.createIndex('name', 'name', { unique: false });
        objectStore.createIndex('email', 'email', { unique: true });
    }
}

function add() 
{
  var request = db.transaction(['person'], 'readwrite')
    .objectStore('person')
    .add({ id: 1, name: 'Jam', age: 24, email: 'jam@example.com' });

  request.onsuccess = function (event) {
    console.log('The data has been written successfully');
  };

  request.onerror = function (event) {
    console.log('The data has been written failed');
  }
}

add();

如能提供任何帮助，将不胜感激。

Answer 1

当db未初始化时，您似乎试图在调用add()期间访问它(请注意，对add()的调用是在执行脚本时立即发生的)。

但是，只有在成功创建数据库连接时才初始化db变量：

request.onsuccess = function (event) 
{
    db = request.result;
    console.log('The database is opened successfully');

    // It is now safe to interact with the database
};

解决这个问题的方法有很多种，不过最简单的方法是将对add()的调用转移到onsuccess处理程序中，如下所示：

request.onsuccess = function (event) 
{
    db = request.result;
    console.log('The database is opened successfully');

    add(); // Add this
};

// add(); <-- remove this from the end of your script

最后，我注意到声明了两个var db;变量--考虑删除其中一个变量。希望这能有所帮助！