Question

我在使用IndexedDB时遇到了麻烦。在Firefox 18上，当我创建一个新数据库时，onsuccess方法同时被调用onupgradeneeded。在Chrome 24上（这是我想要的行为），onsuccess方法仅在onupgradeneeded方法完成后调用。

根据有关IndexedDB的MDN信息，我的印象是，当调用onsuccess方法时，使用数据库是安全的，但这似乎不适用于Firefox。

(function(){
  app = {};

  // These will hold the data for each store.
  app.objectstores = [
    { name: 'UNIVERSITIES',
      keyPath: 'UID',
      autoIncrement: false,
      data_source: 'http://mysites.dev/nddery.ca_www/larelance/data/universite.json' },
  ];

  // Some information pertaining to the DB.
  app.indexedDB    = {};
  app.indexedDB.db = null
  app.DB_NAME      = 'testdb';
  app.DB_VERSION   = 1;

  /**
   * Attempt to open the database.
   * If the version has changed, deleted known object stores and re-create them.
   * We'll add the data later.
   *
   */
  app.indexedDB.open = function() {
    // Everything is done through requests and transactions.
    var request = window.indexedDB.open( app.DB_NAME, app.DB_VERSION );

    // We can only create Object stores in a onupgradeneeded transaction.
    request.onupgradeneeded = function( e ) {
      app.indexedDB.db = e.target.result;
      var db = app.indexedDB.db;

      // Delete all object stores not to create confusion and re-create them.
      app.objectstores.forEach( function( o ) {
        if ( db.objectStoreNames.contains( o.name ) )
          db.deleteObjectStore( o.name );

        var store = db.createObjectStore(
          o.name,
          { keyPath: o.keyPath, autoIncrement: o.autoIncrement }
        );

        app.indexedDB.addDataFromUrl( o.name, o.data_source );
      });
    }; // end request.onupgradeneeded()

    // This method is called before the "onupgradeneeded" has finished..??
    request.onsuccess = function( e ) {
      app.indexedDB.db = e.target.result;
      app.ui.updateStatusBar( 'Database initialized...' );

      // ***
      // Would like to query the database here but in Firefox the data has not
      // always been added at this point... Works in Chrome.
      //
    }; // end request.onsuccess()

    request.onerror = app.indexedDB.onerror;
  }; // end app.indexedDB.open()


  app.indexedDB.addDataFromUrl = function( store, url ) {
    var xhr = new XMLHttpRequest();
    xhr.open( 'GET', url, true );
    xhr.onload = function( event ) {
      if( xhr.status == 200 ) {
        console.log('*** XHR successful');
        // I would be adding the JSON data to the database object stores here.
      }
      else{
        console.error("addDataFromUrl error:", xhr.responseText, xhr.status);
      }
    };
    xhr.send();
  }; // end app.indexedDB.addDataFromUrl()
})();

谢谢！

Answer 1

您可能遇到的一件事是indexeddb中的自动提交功能。如果事务在短时间内变为非活动状态，它将提交事务并关闭它。

在您的情况下，您正在调用异步方法来填充数据，这就是事务可能变为非活动状态的原因。如果你在app.indexedDB.addDataFromUrl（o.name，o.data_source）之后添加一个console.write;您将看到在检索数据之前它将被调用，从而导致事务的提交。这就是调用成功回调时数据不存在的原因。事务的超时可能在Chrome中比在Firefox中更高。它没有在规范中描述，因此它可能因供应商而异。

顺便说一句，如果你想在你的ajax调用中添加数据，你也必须将对象存储作为参数传递。

Answer 2

在if( xhr.status == 200 ) {}内做你必须做的事情从那里调用一个事务，将数据放到objectStore以及你还需要什么

编辑：

我是这样做的，对我有用，只有在插入所有数据并且objectStore可以使用后才会调用oncomplete函数：

var xhr = new XMLHttpRequest();
xhr.open("GET", "http://...", true);
xhr.addEventListener("load", function(){
    if(xhr.status === 200){
        console.info("Data received with success");
        var data = JSON.parse(xhr.responseText);
        var transaction = db.transaction([STORe],'readwrite');
        var objstore = transaction.objectStore(STORE);
        for(i = 0; i < data.length; i++){
            objstore.put(data[i]);
        };
        transaction.oncomplete = function(event){
            //do what you need here
            console.info("Inserted data: " + data.length);
        };
        transaction.onerror = function(event){              
        };
        transaction.onabort = function(event){
        };
        transaction.ontimeout = function(event){
        };
        transaction.onblocked = function(event){
        };                      
    };
}, false);
xhr.send();

为什么在连接到indexedDB时，在onupgradeneeded之前有时会调用onsuccess？

2 个答案: