freeCodeCamp/seed_data/userMigration.js

require('dotenv').load();
var mongodb = require('mongodb'),

  User = require('../models/User.js'),
  newChallenges = require('./challengeMapping.json'),
  secrets = require('../config/secrets');
  mongoose = require('mongoose');

mongoose.connect(secrets.db);

var i = 1;
var stream = User.find({}).skip(0).limit(0).stream();

stream.on('data', function(user) {
  console.log(i++);
  user.save()
})
.on('error', function (err) {
  console.log(err);
}).on('close', function () {
    console.log('done with set');
    stream.destroy();
});

i = 1;

var stream = User.find({'user.needsMigration': true}).skip(0).limit(0).stream();

stream.on('data', function (user) {
  if (user.challengesHash) {
    this.pause();
    console.log(i++);
    user.needsMigration = false;
    var oldChallenges = Object.keys(user.challengesHash).filter(function (key) {
      if (user.challengesHash[key]) {
        user.progressTimestamps.push(user.challengesHash[key] * 1000);
      }
      return user.challengesHash[key];
    });

    newChallenges.forEach(function (challenge) {
      if (oldChallenges.indexOf(challenge.oldNumber) !== -1 && challenge.newId) {
        user.completedCoursewares.push({
          _id: challenge.newId,
          completedDate: user.challengesHash[challenge.oldNumber] * 1000
        });
      }
    });

    user.completedCoursewares.forEach(function (course) {
      var indexOfCourse = user.uncompletedCoursewares.indexOf(course._id) !== -1;
      if (indexOfCourse !== -1) {
        user.uncompletedCoursewares.splice(indexOfCourse, 1);
      }
    });

    user.completedBonfires.forEach(function (bonfire) {
      bonfire.completedDate = bonfire.completedDate * 1000;
      user.progressTimestamps.push(bonfire.completedDate);
    });
  }

  var self = this;
  user.save(function(err) {
    if (err) {
      console.log('woops');
    }
    self.resume();
  });
}).on('error', function (err) {
  console.log(err);
}).on('close', function () {
  console.log('done with set');
  stream.destroy();
  process.exit(0);
});