如何在 for 循环(在每次迭代中产生一个承诺)完成后返回单个承诺? [英] How to return single promise after for loop (which produces a promise on every iteration) is complete?

问题描述

我的 promise 返回代码有问题，我有一个函数 getTagQuotes，其中包含一个 for 循环，该循环可以多次调用 API 以将数据返回到数组中.

I have a problem with my promise return code, I have a function getTagQuotes which contains a for loop which can make multiple calls an API to return data into an array.

我的代码如下:

// If there are tags, then wait for promise here:
if (tags.length > 0) {

    // Setting promise var to getTagQuotes:
    var promise = getTagQuotes(tags).then(function() {
        console.log('promise =',promise);

        // This array should contain 1-3 tags:
        console.log('tweetArrayObjsContainer =',tweetArrayObjsContainer);

        // Loop through to push array objects into chartObj:
        for (var i=0; i<tweetArrayObjsContainer.length; i++) {
            chartObj.chartData.push(tweetArrayObjsContainer[i]);
        }

        // Finally draw the chart:
        chartDirective = ScopeFactory.getScope('chart');
        chartDirective.nvd3.drawChart(chartObj.chartData);
    });
}

我的 getTagQuotes 函数返回承诺:

My getTagQuotes function with the promise return:

function getTagQuotes(tags) {
    var deferred = $q.defer(); // setting the defer
    var url      = 'app/api/social/twitter/volume/';

    // My for loop, which only returns ONCE, even if there are 3 tags
    for (var i=0; i<tags.length; i++) {
        var loopStep = i;
        rawTagData   = [];

        // The return statement
        return GetTweetVolFactory.returnTweetVol(url+tags[i].term_id)
            .success(function(data, status, headers, config) {
                rawTagData.push(data);

                // One the last loop, call formatTagData
                // which fills the tweetArrayObjsContainer Array
                if (loopStep === (rawTagData.length - 1)) {
                    formatTagData(rawTagData);
                    deferred.resolve();
                    return deferred.promise;
                }
            });
    }

    function formatTagData(rawData) {

        for (var i=0; i<rawData.length; i++) {
            var data_array = [];
            var loopNum = i;

            for (var j=0; j<rawData[loopNum].frequency_counts.length; j++) {
                var data_obj = {};
                data_obj.x = rawData[loopNum].frequency_counts[j].start_epoch;
                data_obj.y = rawData[loopNum].frequency_counts[j].tweets;
                data_array.push(data_obj);
            }

            var tweetArrayObj = {
                "key" : "Quantity"+(loopNum+1), "type" : "area", "yAxis" : 1, "values" : data_array
            };

            tweetArrayObjsContainer.push(tweetArrayObj);
        }
    }
}

注意这一行

return GetTweetVolFactory.returnTweetVol(url+tags[i].term_id)

它在我的 for 循环中:

it's inside my for loop:

for (var i=0; i<tags.length; i++)

如果我只需要循环一次，一切都很好.然而，只要有另一个标签(最多 3 个)，它仍然只返回第一个循环/数据.它不会等到 for 循环完成.然后返回承诺.所以我的 tweetArrayObjsContainer 总是只有第一个标签.

Everything works great if I only have to loop through once. However as soon as there is another tag (up to 3) it still only returns the first loop/data. It does not wait till the for loop is done. Then return the promise. So my tweetArrayObjsContainer always only has the first tag.

推荐答案

三个问题:

1. 您没有从 getTagQuotes 方法返回延迟承诺.
2. 你正在查看 i 是否通过循环，并且 for 循环已经完成 (i == (tags.length - 1))在调用第一个成功之前.
3. 您在循环的第一次迭代中调用了 return，因此您甚至没有到达第二个项目.

1. you didn't return the deferred promise from the getTagQuotes method.
2. you were looking at i to see if you were through the loop, and the for loop is already completed (i == (tags.length - 1)) before the first success is even called.
3. you called return in the first iteration of the loop so that you didn't even get to the 2nd item.

这是更正后的代码(尚未测试)

Here's corrected code (didn't test it yet)

function getTagQuotes(tags) {
    var deferred = $q.defer(); // setting the defer
    var url      = 'app/api/social/twitter/volume/';
    var tagsComplete = 0;

    for (var i=0; i<tags.length; i++) {
        rawTagData   = [];
        GetTweetVolFactory.returnTweetVol(url+tags[i].term_id)
            .success(function(data, status, headers, config) {
                rawTagData.push(data);
                tagsComplete++;

                if (tagsComplete === tags.length) {
                    formatTagData(rawTagData);
                    deferred.resolve();
                }
            });
    }

    return deferred.promise;
}

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