检查IndexedDB数据库是否存在 [英] Check if IndexedDB database exists

问题描述

是否可以检查IndexedDB数据库是否已存在?当程序尝试打开不存在的数据库时，将创建该数据库. 我能想到的唯一方法是如下所示，在这里测试objectStore是否已经存在，如果不存在，则删除数据库:

Is there a way to check if an IndexedDB database already exists? When a program tries to open a database that does not exists the database is created. The only way that I can think of is something like the following, where I test if an objectStore already exists, if it doesn't, the database is deleted:

var dbexists=false;
var request = window.indexedDB.open("TestDatabase");
request.onupgradeneeded = function(e) {
    db = e.target.result;
    if (!db.objectStoreNames.contains('todo')) {
       db.close();
       indexedDB.deleteDatabase("TestDatabase");
    } else {
       dbexists=true;
    }
}

推荐答案

在onupgradeneeded回调中，您可以检查版本. (e.target.result.oldversion).如果 它是0，数据库不存在.

In the onupgradeneeded callback you can check the version. (e.target.result.oldversion). If it is 0, the db didn't exist.

经过一番调查.您不能100％确定是否创建了新的数据库.我确定的一件事是，只有indexeddb的版本为1或更高版本时，您才可以使用它.我相信一个数据库可以存在并具有版本0(唯一的事实是您不能使用它，并且将调用onupgradeneeded事件).

After some investigation. You can't be 100% sure if a new db is created. 1 thing I am sure of is the fact that you can only work with an indexeddb if it has a version 1 or higher. I believe that a db can exist and have a version 0 (The only fact is you can't work with it and the onupgradeneeded event will be called).

我已经建立了自己的indexeddbviewer.在这种情况下，我打开没有版本的indexeddb，如果我进入onupgradeneeded事件，则意味着该数据库不存在.在这种情况下，我将异常终止称为中止"，这样它就不会升级到版本1.这是我检查它的方式.

I have build my own indexeddbviewer. In that I open the indexeddb without version and if I come in to the onupgradeneeded event, that means the db doesn't exist. In that case I call the abort so it doesn't upgrade to a version 1. This is the way I check it.

var dbExists = true;
var request = window.indexeddb.open("db");
request.onupgradeneeded = function (e){
    e.target.transaction.abort();
    dbExists = false;
}

但如上所述.在这种情况下，数据库可能会继续存在，但是onupgradeneeded将始终被调用

but as mentioned. It is possible that the db will continue to exist in that case, but the onupgradeneeded will always be called

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