为什么连接索引资料时的onSuccess有时会调用之前onupgradeneeded？ [英] Why does onsuccess sometimes get called before onupgradeneeded when connecting to indexedDB?

问题描述

我有IndexedDB的麻烦。在Firefox 18，当我创建一个新的数据库，在的onSuccess 方法被调用，同时具有 onupgradeneeded 。在Chrome 24（这是我想要得到的行为），在的onSuccess 方法是在 onupgradeneeded 方法完成。

I am having trouble with IndexedDB. On Firefox 18, when I create a new database, the onsuccess method is called at the same time has onupgradeneeded. On Chrome 24 (this is the behavior I'd like to get), the onsuccess method is only called after the onupgradeneeded method has completed.

据对索引资料的MDN信息，我是IM pression下，当的onSuccess方法被调用，这是安全与数据库的工作，但本作看起来它是不能在Firefox。

According to the MDN information on IndexedDB, I was under the impression that when the onsuccess method was called, it was safe to work with the database but this make it seems like it is not in 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！

推荐答案

一个你可能患上同的事情是在IndexedDB的自动提交功能。如果交易很短的时间跨度变为无效，就会提交事务并关闭它。

One of the things you are probably suffering with is the auto-commit functionality in the indexeddb. If an transaction becomes inactive for a short timespan, it will commit the transaction and close it.

在你的情况你调用一个异步方法来填充数据，这就是为什么该交易可能变为无效。如果后添加console.write app.indexedDB.addDataFromUrl（o.name，o.data_source）;你将看到的是检索数据前，将被调用，从而导致该交易的提交。这就是为什么数据是不是当成功回调被称为present。这可能是进行交易的超时是比铬在Firefox更高。这不是在描述规范，因此它可以通过供应商而异。

In your case you are calling an async method to fill up the data, and that is why the transaction probably becomes inactive. if you add a console.write after app.indexedDB.addDataFromUrl( o.name, o.data_source ); you will see it will get called before your data is retrieved, causing the commit of the transaction. That is why the data isn't present when the success callback is called. It is possible that the timeout for transactions is higher in chrome than in Firefox. It isn't described in the spec so it can vary by vendor.

顺便说一句，如果你想在你的Ajax调用添加数据，你将不得不通过对象存储作为参数也是如此。

btw, if you want to add data in your ajax call, you will have to pass the object store as a parameter as well.

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