javascript - 从indexeddb分段加载数据

Question

我正在使用 IndexedDB，我有一个包含大约 4000 条记录的数据库。我试图一次加载一小块记录。类似于您在推特上看到的无限滚动。我尝试用谷歌搜索这个并没有找到代码示例，但遇到了高级方法。我尝试使用它，但仍然没有成功。浏览器一次加载所有记录。如何才能一次只加载少量记录？

var openRequest = indexedDB.open("USA", 1);

        openRequest.onsuccess = function (e) {
            var db = e.target.result;
            var transaction = db.transaction(["Male"], "readonly");
            var objectStore = transaction.objectStore("Male");
            var cursor = objectStore.openCursor();

            cursor.onsuccess = function (e) {
                var res = e.target.result;

                if (res) {
                    res.advance(25);
                    res.continue();
                    console.log(res.value);
                }
            }
        }

Answer 1

res.advance(25) 将跳过 25 行，但仍会加载其余行。我更改了你的代码+添加了一些评论。您可能想使用这样的东西:

var openRequest = indexedDB.open("USA", 1);

openRequest.onsuccess = function (e) {
    var db = e.target.result;
    var transaction = db.transaction(["Male"], "readonly");
    var objectStore = transaction.objectStore("Male");
    var cursor = objectStore.openCursor();
    var results = null; // variable to store the results
    var startIndex = 25,
        maxResults = 25;

    cursor.onsuccess = function (e) {
        var res = e.target.result;

        if (res) {
            if (!results) {
                results = [];
                // skip rows, but only the first time
                res.advance(startIndex);
            } else {
                results.push(res.value)
                // We don't have 25 results yet, continue to load a next one
                if(results.length < maxResults) {
                    res.continue();
                }
            }
        }
    }
    transaction.oncomplete = function() { 
        // maxResults loaded or maybe it was the last page so it might not be full
        console.log(results);
    }
}

下面的示例要简单得多，并且可以使用自动增量，但只有在未删除结果时页面才会满(不是完整的代码，但都是关于 IDBKeyRange.bound(0, 25) 的)

var cursor = objectStore.openCursor(IDBKeyRange.bound(0, 25));
var results = [];
cursor.onsuccess = function (e) {
    var res = e.target.result;
    if (res) {
        results.push(res.value)
    }
}
transaction.oncomplete = function() { 
    console.log(results);
}