Question

我对JS和函数式编程非常陌生，我很难找到一个优雅的解决方案来解决这个问题。本质上，我想向MongoDB服务器发出异步请求，并将结果返回到async to map函数。我遇到的问题是async.map中的实际函数本身就是异步的。我想在这里知道一个优雅的解决方案，或者至少得到一个指向正确方向的指针！谢谢！

  async.map(subQuery,
    function(item){
      collection.distinct("author", item, function(err, authors){
        counter++;
        console.log("Finished query: " + counter);

        var key = item['subreddit'];
        return { key: authors };
      })
    },

    function(err, result){
      if (err)
        console.log(err);
      else{
        console.log("Preparing to write to file...");

        fs.writeFile("michaAggregate.json", result, function() {
          console.log("The file was saved!");
        });
      }

      db.close();
    }
  );

Answer 1

只有在获取数据时才应处理项目。只需使用回调即JavaScript的常用方法。像这样：

var processItem = function(item){  
// Do some street magic with your data to process it

// Your callback function that will be called when item is processed.
onItemProccessed();
}

async.map(subQuery,
function(item){
  collection.distinct("author", item, function(err, authors){
    counter++;
    console.log("Finished query: " + counter);

    var key = item['subreddit'];
    processItem(item);
  })
},

function(err, result){
  if (err)
    console.log(err);
  else{
    // That string added **ADDED** 
    console.log('HEEY! I done with processing all data so now I can do what I want!');
    console.log("Preparing to write to file...");

    fs.writeFile("michaAggregate.json", result, function() {
      console.log("The file was saved!");
    });
  }

  db.close();
}
);

<强> ADDED

根据async.map的规范，您可以看到：

https://github.com/caolan/async

async.map(arr, iterator, callback):

callback(err, results) - A callback which is called when all iterator functions have finished, or an error occurs. Results is an array of the transformed items from the arr.正如您所看到的，回调正是您所需要的！

在Async.map中撤消异步函数的结果

1 个答案: