Handling loop with nodejs asynchronous callback

Question

I'm new to nodejs and mongoose. I have a database dated from 2009 until now and would like to count number of data of each month, and return as json array. Slow async callback results all dates as Aug. 1, 2014

What is the proper way to implement this?

var dbURL = 'mongodb://localhost/database';
var db = require('mongoose').connect(dbURL);
var c_db = require('./models/models.js').c_db;

var start_date = new Date(2009,0,1);
end_date = new Date(2014,8,1),
next_date = new Date();

var test_json=[];

var total_months = (end_date.getFullYear() - start_date.getFullYear())*12 + (end_date.getMonth() - start_date.getMonth());

var next_date = start_date;

for(var i=0;i<total_months;i++){

  var firstDay = new Date(next_date.getFullYear(), next_date.getMonth(), 1);
  var lastDay = new Date(next_date.getFullYear(), next_date.getMonth() + 1, 0);
  next_date.setDate(lastDay.getDate()+1);

  c_db.count({'shipdate':{'$gte':new Date(firstDay),'$lte':new Date(lastDay)}},function(err,query){

    var item = {
      "Date": firstDay,
      "Count": query
    }
    test_json.push(item);
  });

}

setTimeout(function(){
  console.log(test_json);
},5000);

c_db.count({'shipdate':{'$gte':new Date(firstDay),'$lte':new Date(lastDay)}},function(err,query){ why are you doing new Date(firstDay)? Are those not already date objects? — royhowie
– royhowie, Commented Sep 2, 2014 at 17:54
firstDay and lastDay were hardcoded at the beginning, thx for mentioning :) — fluidsnake
– fluidsnake, Commented Sep 2, 2014 at 18:11
I guess you could define a callback function, whenFinished, that's called when test_json.length === i - 1. Because of closures, if you put this after test_json.push(item), it'll call it, even if the for loop has finished looping. So something like if (condition) whenFinished() on the line after test_json.push should work. — royhowie
– royhowie, Commented Sep 2, 2014 at 22:42

Comtaler · Accepted Answer · 2014-09-02 21:46:04Z

Be careful when you are writing javascript with async callbacks. What you want to do is to continue to the next item in the loop when the current async is finished. You can use a the "async" module: https://github.com/caolan/async

var async = require("async");
var dbURL = 'mongodb://localhost/database';
var db = require('mongoose').connect(dbURL);
var c_db = require('./models/models.js').c_db;

var start_date = new Date(2009,0,1);
end_date = new Date(2014,8,1),
next_date = new Date();

var test_json=[];

var total_months = (end_date.getFullYear() - start_date.getFullYear())*12 + (end_date.getMonth() - start_date.getMonth());

var next_date = start_date;

async.timesSeries(total_months, function(n, next) {
  var firstDay = new Date(next_date.getFullYear(), next_date.getMonth(), 1);
  var lastDay = new Date(next_date.getFullYear(), next_date.getMonth() + 1, 0);
  next_date.setDate(lastDay.getDate()+1);

  c_db.count({'shipdate':{'$gte':new Date(firstDay),'$lte':new Date(lastDay)}},function(err,query){

    var item = {
      "Date": firstDay,
      "Count": query
    }
    test_json.push(item);
    next();
  });
}, function(e) {
  console.log(test_json);
});

Collectives™ on Stack Overflow

Handling loop with nodejs asynchronous callback

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related