Question

我已经看到多个JavaScript示例使用createIndex在ObjectStore创建后直接定义ObjectStore索引：

var objectStore = ixDb.createObjectStore(osName, { keyPath: pkName, autoIncrement: autoIncrement });

objectStore.createIndex("name", "name", { unique: false });

有人可以告诉我如何在不调用createIndex的情况下在预先存在的桌子上使用createObjectStore吗？我想这里真正的问题是如何在不使用createObjectStore的情况下获取对objectStore的引用？

我尝试了以下几种变体而没有运气：

var objectStore = window.IDBTransaction.objectStore(ObjectStoreName);
var index = objectStore.createIndex(ixName, fieldName, { unique: unique, multiEntry: multiEntry });

Answer 1

你在onupgradeneeded期间这样做，它应该与你首先制作对象存储的地方相同。在那里，您可以执行升级所需的任何操作，例如创建新索引。 Here is an example.

Answer 2

Chrome目前不支持onupgradeneeded事件。如果您想使用旧的或新的W3规范获得对ObjectStore的引用，这是使用旧的setVersion命令或通过新的onupgradeneeded事件通过onsuccess事件的一种可能的解决方法：

var ixDb; 
var ixDbRequest; 
var ixDbVersionTansaction;

//Check to see if we have a browser that supports IndexedDB
if (window.indexedDB) {

ixDbRequest = window.indexedDB.open(dbName, dbVersion);

//For browsers like chrome that support the old set version method
ixDbRequest.onsuccess = function (e) {

    ixDb = ixDbRequest.result || e.result;

    if (typeof ixDb.setVersion === "function") {

        //Put your version checking logic here 

        if (oldVersion < newVersion) {
            var verRequest = ixDb.setVersion(newVersion);

            verRequest.onerror = function (e) {
                //handling error logic here
            }

            verRequest.onsuccess = function (e) {
                //Get a reference to the version transaction 
                //from the old setVersion method.
                ixDbVersionTansaction = verRequest.result;
                //Create database using function provided by the user. 
                UserFunction();
            }
        }
    }
}; 

ixDbRequest.onupgradeneeded = function (e) {
    //FF uses this event to fire the transaction for upgrades.  
    //All browsers will eventually use this method. Per - W3C Working Draft 24 May 2012
    ixDb = ixDbRequest.result || e.currentTarget.result;

    //Get a reference to the version transaction via the onupgradeneeded event (e)
    ixDbVersionTansaction = e.currentTarget.transaction;

    //Create database using function provided by the user. 
    UserFunction();
};

UserFunction(){
    //ObjectStore is accessed via ixDbVersionTansaction variable 
    // in either instance (transaction..objectStore("ObjectStoreName"))
    var ObjectStore = ixDbVersionTansaction.objectStore("ObjectStoreName");
    var index = ObjectStore.createIndex("ixName", "fieldName");
}

使用Javascript在IndexedDB中为预先存在的ObjectStore添加索引

2 个答案: