Question

好的，这里有很多事情发生，但我试图尽可能地解决这个问题。

在我的node.js Express项目中，我进行了两次API请求调用，第二次调用依赖于第一次调用。为了简化此任务，我使用异步模块中的瀑布方法。

在getVideoDetails函数中，我将第二个API请求置于循环中，并从第一个响应中检索videoId以获取视频数据。

目前我遇到的问题是，var extended只给我body值，而我预计会result + body。

我想知道这是因为_extend不应该在循环中。我还不清楚如何在循环外调用回调（结果）来使结果可访问。

async.waterfall([

    function getVideos (getVideoCallback) {

        ...

    },

    function getVideoDetails (result, getVideoDetailsCallback) {

        var urls = [];

        Object.keys(result.items).forEach(function(item) {
            urls.push ("https://www.googleapis.com/youtube/v3/videos?part=contentDetails&id=" + result.items[item].contentDetails.videoId + "&key=xxx");
        })

        urls.forEach(function(url) {
            request( url, function(err, response, body) {
                if(err) { console.log(err); return; }
                body = JSON.parse(body);    

                var extended = _.extend(result, body);

                getVideoDetailsCallback(null, extended);

            });
        });

    }
], function (err, result) {

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

    callback(result);

});

Answer 1

如果你想按顺序做这些事情......

1. Generate an array asynchronously
2. Do some asynchronous process for each item in the array
3. Do something asynchronous after you have processed the array

...那么这是使用异步库可以实现的一种方式。

var request = require("request");
var _ = require("lodash");
var db = require("whatever you are using");

module.exports = function(req, res) {
    var params = req.params;

    async.waterfall([

        function getVideos(next) {
            db.findAll().then(function(rows) {
                next(null, rows);
            });
        },

        function forEachVideoDoSomethingAsync(videos, next) {
            var urls = videos.map(function(obj) {
                obj.url = obj.name + "http://googleapi.com/whatever";
                return obj;
            });

            /** this is the part you are missing **/

            //async.map takes three arguments
            //1. the array you want to work on
            //2. a function that is applied to each item in the array
            //    the iterator function receives two arguments
            //    1. the current item in the array
            //    2. a callback you invoke when you want to move to the next item
            //3. a callback that is executed once the loop has been completed

            async.map(urls, function(currentItem, callback) {
                request(currentItem.url, function(err, response, body) {
                    if (err) 
                        return console.log(error);
                    //you probably have to extend the current item in the array with the response object
                    var json = JSON.parse(body);
                    var extended = _.extend(currentItem, json);
                    //each item you send via the callback will be pushed into the result of async.map
                    callback(extended);
                });
            }, function(err, urls_extended) {
                //urls_extended is now an array of extended items
                //now you have to exit the waterfall
                next(null, urls_extended);
            });

        }

    ], function(err, urls_extended) {
        if (err) 
            return console.log(err);
        //exit the entire process
        res.send(urls_extended);
    })

};

Node.js - 使用async.waterfall的依赖API请求调用，并使用underscore.extend合并JSON响应

1 个答案: