我正在尝试从嵌套的 for 循环中提取值。我的循环从 Redis 获取值，我想将这些值添加到名为“info”的数组变量中。

重要的一点是 for 循环。

app.get('/query', function(req, res) {

    var info = [];

    redisClient.keys("todo:*", function(err, data) {            

        if (err) return console.log(err);

        for (var i = 0, len = data.length; i < len; i++) {
            var id = data[i];
            var listItem, author, goodness;

            redisClient.hgetall(data[i], function(err, obj) {
                listItem = obj.listItem;
                author = obj.author;
                goodness = {
                    id: id,
                    listItem: listItem,
                    author: author
                }
                info.push(goodness);
                console.log("In here: " + info);

            }); 
            console.log("Out here: " + info);
        }
        console.log("Way out here: " + info);
    }); 
    console.log("WAY THE HECK OUT HERE: " + info);
});

基本上，我希望将变量“goodness”中的值推送到名为“info”的数组变量中。当我执行代码时，信息数组会在这里填满，

console.log("In here: " + info);

but I have not found a way to extract the info array to have values outside of the redisClient.hgetall() function. I have tried return statements to no avail, though as a beginning programmer there is a decent chance I'm not doing these properly.

NOTE: I have tried to take guidance from the original answer and I must be doing something wrong, or the solution given wasn't good enough, or both. I have added the Q library to my project, and have tried to find a solution. Here is my current code:

app.get('/query', function(req, res) {

    var redisKeys = Q.nbind(redisClient.keys, redisClient);
    var redisHGetAll = Q.nbind(redisClient.hgetall, redisClient);
    var id, listItem, author;

    var info = [];

    redisKeys('todo:*').then(function (data) {
        console.log("First: " + data);
       var QAll = Q.all(data.map(processKeysFunc(info)));
       console.log("Reading within this: " + data);
       console.log("Next within this: " + QAll);
    }, function (err) { 
        if (err) return console.log(err);
        }).then(function () {
       console.log("Finally: " + data);

    })();

    function processKeysFunc(array) {
        return function (key) {
            console.log("This is the key: " + key);
            return redisHGetall(key).then(function (obj) {
                console.log("This is the obj: " + obj);
                array.push({
                    id: obj.id,
                    listItem: obj.listItem,
                    author: obj.author
                });
            });
        };
    }
});

这是我在 console.log 中得到的:

First: todo:281f973d-6ffd-403b-a0f4-9e8958caed35,todo:7ed8c557-0f15-4555-9119-
6777e1c952e8,todo:eb8dbee1-92ca-450e-8248-ad78548cd754,todo:712e8d27-bf9b-46f0-bfdd-
c53ef7d14441,todo:301dd91a-2b65-4b87-b129-a5ad569e38e5,todo:720d98b8-bdec-446d-a178-
fb7e264522aa,todo:d200c6cf-2ee5-443b-b7dc-d245c16899c8,todo:8169e9af-0204-42c8-9ddf-
3b00f7161b11

This is the key: todo:281f973d-6ffd-403b-a0f4-9e8958caed35

最佳答案

node.js 通常是非阻塞的，这就是使用回调的原因。传递给 .hgetall 的回调只会在完全接收到来自 redis 的数据时执行。它周围的其余代码将立即执行，而不是等待来自 redis 的数据。事实上，由于 .hgetall 调用可能涉及 IO，因此回调将始终在周围代码执行后运行。

您有几种选择，包括使用 Promises ( https://github.com/kriskowal/q )。

我将建议一个解决方案，该解决方案应该可以理解您的代码的当前结构:

app.get('/query', function(req, res) {

    var info = [];
    var completed = 0;

    redisClient.keys("todo:*", function(err, data) {            

        if (err) return console.log(err);

        for (var i = 0, len = data.length; i < len; i++) {
            var id = data[i];
            var listItem, author, goodness;

            redisClient.hgetall(data[i], function(err, obj) {
                completed++;
                if (err) return console.log(err);

                listItem = obj.listItem;
                author = obj.author;
                goodness = {
                    id: id,
                    listItem: listItem,
                    author: author
                }
                info.push(goodness);
                console.log("In here: " + info);

                if (completed === data.length) {
                    // Do something with info here, all work has finished
                }

            }); 
            console.log("Out here: " + info);
        }
        console.log("Way out here: " + info);
    }); 
    console.log("WAY THE HECK OUT HERE: " + info);
});

关键位是新变量 completed，它跟踪返回了多少回调。

不过，我强烈建议改用 promises。像这样的东西:

var Q = require('q');

var redisKeys = Q.nbind(redisClient.keys, redisClient);
var redisHGetall = Q.nbind(redisClient.hgetall, redisClient);

app.get('/query', function(req, res) {
    var info = [];
    redisKeys('todo:*').then(function (data) {
        return Q.all(data.map(processKeysFunc(info));
    }, function (err) { /* handle error */ }).then(function () {
       console.log('Complete info array=%j', info);
       res.setHeader('Content-Type', 'application/json');
       res.end(JSON.stringify(info));
    });
});

function processKeysFunc(array) {
    return function (key) {
        return redisHGetall(key).then(function (obj) {
            var goodness = {
                id: key,
                listItem: obj.listItem,
                author: obj.author
            };
            array.push(goodness);
        });
    }
}

processKeysFunc 返回一个函数，以便您可以干净地传递 info 数组，而无需定义每个内联函数。如果您更喜欢内联，那也行。

关于javascript - 在嵌套 for 循环中获取值 - node.js、javascript、redis、Q 库，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27778042/