NodeJs Mongoose循环收集数据

Question

Hope for your help.

I have collection tasks with document like this schema.

Task = { 
     title:'taskName', 
     performers:[ {userId:1,price:230}, {userId:2,price:260} ]
}   
Profiles = { id:1, name: 'Alex', surname: 'Robinson', etc.. }

Finally, I shoul collect all data, and in response return Array of profiles objects. Problem is that for-loop end before finished all .findOne() for every elements, and it return empty Array. This is code form get.

CODE HERE:

apiRoutes.get('/performers/:id', function(req,res,next){

var profArr = []; 
Task.findOne({'_id':req.params.id},function(err, doc){
  for(var i = 0; i<doc.performers.length; i++){
    var profile = {
      price: 0,
      name: '',
      surname: ''         
    };
    profile.price = doc.performers[i].price;
    Profile.findOne({'_id':doc.performers[i].userId},function(err,doc){
      if (err) throw err;
      profile.name = doc.name;
      profile.surname = doc.surname;          
      profArr.push(profile);
    });
  }
  return res.json({success:true,
                   message:'Performers data collected',
                   data:profArr});
});    

Answer 1

A simple idea would be to introduce a countdown-counter before you start your for-loop like this:

var countdown = doc.performers.length;

Decrement the countdown in the callback function of the findOne-Calls. Check if you have reached 0 and call a function outside to send the result.

But still your code doesn't look very efficient. There are a lot of calls to the db. Maybe you could rethink your datamodel in order to minimize the calls to the db.

Answer 2

The problem is you need to return response inside mongoose query. You can't use any values assigned inside the query outside. For example :

var sampleArr = [];
Users.find({}, function(err, users) {
  users.forEach(function(user) {
    Students.find({'userid' : user.id}, function(err, student) {
      sampleArr.push({
        'student' : student
      });
    })
    console.log(sampleArr);
    // It will only return empty array[];
  })
})

So, your task should be like this:

apiRoutes.get('/performers/:id', function(req,res,next){

var profArr = [];
// Get a task by ID
Task.findById(req.params.id, function (err, task) {
  // Get all profiles
  Profile.find({}, function (err, profiles) {
    task.performers.forEach(function(taskPerformer) {
      profiles.forEach(function(profile) {
        // Check the performer ID is the same with userID or not
        if (profile._id == taskPerformer.userId) {
          profArr.push({
            price: taskPerformer.price,
            name: profile.name,
            surname: profile.surname
          });
        }
      })
    });
    return res.json({
      success:true,
      message:'Performers data collected',
      data:profArr
    });
  });
})

Answer 3

您的“ for”循环将在findOne完成之前完成。