如何同步访问indexedDB？ [英] How can I access indexedDB synchronously?

问题描述

indexedDB有规范，说明您可以同步访问索引数据库，但它还没有实现。

The indexedDB has a spec saying that you can access an indexed database synchronously, but it hasn't been implemented yet.

我只是想知道是否有办法让它手动同步，

I was just wondering if there is a way to make it synchronous manually,

我的JavaScript看起来像这样，

My JavaScript looks like this,

var trans = databaseAsync.transaction(["mapTile"], IDBTransaction.READ_WRITE);
var store = trans.objectStore("mapTile");
var keyRange = IDBKeyRange.bound(evt.data[0], evt.data[0]);
var cursorRequest = store.openCursor(keyRange);

// can you put some kind of wait in here?

cursorRequest.onsuccess = function(e)
{
    var result = e.target.result;
    if(!!result == false)
    {
    }
}

那么你可以在那里放一些东西让它等到onsuccess方法被调用后再继续吗？

So can you put something in there to make it wait until the onsuccess method has been called before continuing on?

我想要的原因这是上面的代码包含在这个方法中，

The reason why I want to do this is the code above is wrapped inside this method,

dojo.extend(esri.layers.ArcGISTiledMapServiceLayer, {
      getTileUrl : function(level, row, col)
      {
          // blah
          return url;
      }

所以它是一个ESRI图块层（它会将图块加载到我的网页上的地图上），并且该方法需要立即返回特定图块的网址。它将是一个加载图像的URL，如果它没有缓存在数据库中，或者这个，

So it is an ESRI tile layer (which will load tiles onto a map on my web page), and that method needs to return the url straight away for a particular tile. It will either be a URL to load the image from if it isn't cached in the database already, or this,

data:image;base64,*BASE64DATA*

其中 BASE64DATA 是来自的数据以前缓存的数据库。

Where BASE64DATA is the data from the database if previously cached.

我是s之前使用localStorage，它同步工作，但是有5MB限制，所以我想我会尝试使用indexedDB。

I was previously using the localStorage for this, which works synchronously, but that has a 5MB limit so I thought I would experiment with indexedDB.

推荐答案

几个月前我问过的这个问题的接受答案。不幸的是，它依赖于仅在Firefox中支持的JavaScript 1.7（生成器）的功能。希望有一天这种技术会得到更广泛的支持。

An elegant way of doing this is provided in the accepted answer to this question I asked a couple months ago. Unfortunately, it relies on feature of JavaScript 1.7 (generators) that is only supported in Firefox. Hopefully some day this technique will be more widely supported.

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