如何保证异步调用是从猫鼬函数返回前执行？ [英] How to ensure an asynchronous call is executed before returning from a function in Mongoose?

问题描述

我是新来的猫鼬，为了地狱prevent异步I碰到所谓的异步。我已经使用了 async.series 的异步 NPM包，我的code看起来在下面

I am new to mongoose and in order to prevent ASYNC OF HELL I came Across an npm package called async. I have used the async.series of the async npm package and my code looks in the given format given below

var userId=1234
function findUser(callback){
  user.findOne({userId:userId}).exec(function(err,userData){
         //Some Logic
   var schoolId=123;
   var schoolName=findSchool(123);     
   findStudents(schoolName);

   var schoolId=1234;
   var schoolName=findSchool(123);     
   findStudents(schoolName);

   callback(null);
  });
}

function findSchool(schoolId){
 school.findOne({schoolId:schoolId}).exec(function(err),schoolDetails){
    //Some Logic  
  });
    var schoolName="XYZ High School"
    return(schoolName);
}

 function findStudents(schoolName){
  student.findOne({schoolName:schoolName}).exec(function(err),studentDetails{
    //Some Logic  
  });
 }

 async.series([findUser],function(err){
     // for Error Handling
    }

在这里，我使用的是异步系列函数prevent地狱异步。我打电话异步系列电话是找到我的用户用户详细信息 findUser 函数模型使用用户id 然后我打电话了 findSchool 函数的 的内部 findUser 功能，发现学校的详细信息对于给定的 SchoolId 在学校模式。一旦该函数返回调用我想找到根据特定学生的 schoolName 用 findStudents 功能学生模式。

Here I am using an async series function to prevent the ASYNC of HELL. I am calling findUser function in the async series call which is find the user details from my User model using the userId and then I am calling the findSchool function inside the findUser function which finds school details for the given SchoolId in School model. Once the function returns the call I am trying to find the students based on a particular schoolName using the findStudents function on the Student model.

此过程重复进行不同的 schoolId 。我的问题是当我叫 findSchool 功能。由于它的学模型异步调用（ findOne ），我能够返回的值 schoolName 甚至在 findOne 为模型。

The process is repeated for a different schoolId. My Issue comes when I call the findSchool function. Since it has a asynchronous call (findOne) on the school model, I am able to return the value of the schoolName even before the findOne is completed for the model.

有没有一种方法，以确保给定函数 findSchool 不返回的值 schoolName 直到在 school.findOne（）已成功完成？我想补充更清晰我的不要的我return语句的 的对应的<$ C的 findOne $内C> findSchool 功能。

Is there a way to ensure that the given function findSchool doesn't return the value of the schoolName until the school.findOne() has completed successfully? Just to add more clarity I don't want to my return statement inside the findOne of the findSchool function.

推荐答案

您应该仍然可以使用异步，但你需要 async.waterfall 为。下面是你需要考虑的内容：

You should still use async but you need async.waterfall for that. Here is what you need to consider:

一个主要方法调用你的异步功能：

A main method to call your async function:

var getInformation = function(){
  async.waterfall([
    //Array of your functions in order, we will be back here later
  ], function (err) {
       if(err){
         console.log(err);
       }else{
         console.log('Everything OK!');
     }
  );
}

然后你需要你的职责是异步友好的，这意味着你应该使用回调，让你的数据从一个功能到另一个。事情是这样的：

Then you need your functions to be async friendly, that means you should use callbacks and give your data from one function to another. Something like this:

function findUser(callback){
  //Do something
  if('Everything OK'){
    callback(err, yourData); //err should be null if everything is OK and yourData should be the data that you wanna use in your next function. e.g. schoolId 
  }else{
    callback(err); //Something was wrong, "err" should have something different to null
  }
}

function findSchool(callback, schoolId){ //Note that we receive the parameter schoolId here but not in the first function
  //Do something
  if('Everything OK'){
    callback(err, yourData); //err should be null if everything is OK and yourData should be the data that you wanna use in your next function. e.g. schoolName 
  }else{
    callback(err); //Something was wrong, "err" should have something different to null
  }
}

function findStudents(callback, schoolName){
  //Do something
  if('Everything OK'){
    callback(err); //err should be null if everything is OK if this is the last function maybe we don't need to send back more data from here 
  }else{
    callback(err); //Something was wrong, "err" should have something different to null
  }
}

那你应该打电话给你的函数main方法：

Then you should call your functions in your main method:

var getInformation = function(){
  async.waterfall([
    findUser,
    findSchool,
    findStudents
    //Note that there is no need to tell the functions the parameters they are sending or receiving here
  ], function (err) {
       if(err){
         console.log(err);
       }else{
         console.log('Everything OK!');
     }
  );
}

就是这样，你必须应对方，没有回调地狱后，需要执行的一个3个功能。

And that's it, you have 3 functions that should be executed one after the other and no callback hell is needed.

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