如何等待猫鼬查询的结果? [英] How to wait for the result of a mongoose query?

问题描述

我尝试根据猫鼬查询的结果过滤数组.标准过滤器函数期望回调返回true或false.我的麻烦是该信息取决于猫鼬findOne查询的异步结果

I try to filter an array according to the result of a mongoose query. The standard filter function expect the callback to return true or false. My trouble is that this information depends on the asynchronous result of a mongoose findOne query

# code that does not work
myArray.filter = (elem) ->
  MyCollection.findOne {_id : elem}, (err,elem) ->
    result = err==null
  #Need to wait here for the result to be set
  result

有人知道如何解决此类问题吗?

Anyone has a clue how to resolve that kind problem ?

我也尝试使用异步过滤器功能，但我认为它不适用于我的情况(或者我可能不太了解)

I tried as well to use the async filter function but I don't think it works in my case (or I maybe I don't understand well)

这是我对异步过滤器的理解，以及为什么(我认为)它不能解决我的问题:

Here is my understanding of async filter and why (I think) it can't solve my problem :

// code that doesn't work
async.filter(myArray, function(elem){
  var result = true;
  MyCollection.findOne({_id : elem}, function(err,elem) {
    result = err==null;
  });
  // the filter exits without waiting the update done asychronously in the findOne callback
  return result;
}, 
function(results){
  // results now equals an array of the existing files
});

推荐答案

使用 filter 可以从async库中获取.

更新

您的尝试非常接近，您只需要将结果提供给回调即可，而不是返回它:

You're pretty close in your attempt, you just need to provide the result to the callback instead of returning it:

async.filter(myArray, function(elem, callback){
  MyCollection.findOne({_id : elem}, function(err, doc) {
    callback(err == null && doc != null);
  });
}, 
function(results){
  // results is myArray filtered to just the elements where findOne found a doc
  // with a matching _id.
});

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