Purging Data Logic in MongoDb based on Dates - node.js

Question

I am unable to think of logic for the following Issue.
Consider I want to Store Data in mongoose in collection called packet where I can store data of different users. I want to purge the data once a certain threshold has been reached (Say for example 10 days). We know that the Mongoose by default gives us CreatedAt and UpdatedAt fields.
Suppose my data is created at 22nd February 2015 and Current Date is 24th February 2015.I will have a PurgeData number(column used for purging of data) as 2 (difference between the two dates). Every day I want to change the value of the PurgeData number by comparing the difference between the current date and the CreatedAt date. I want to schedule this operation every day and delete the data that has reached the threshold so I save memory space. Can Somebody help me with the logic for it and scheduling of the event?
Thanks in Advance

Answer 1

Haven't actually tried this but I would suggest some logic like schedule a job using the mongo-scheduler package where you first do an update and then remove the documents that breach the PurgeData condition. Something like this (untested):
/*
Scheduler Arguments
connection - mongodb connections string (i.e.: "mongodb://localhost:27017/scheduler-db") or a mongoose connection object
options - Options object
*/
var mongoose = require('mongoose');
var Scheduler = require('mongo-scheduer');
var scheduler = new Scheduler(connection, options);
var packet = new mongoose.Schema({
CreatedAt : {type : Date, default: Date.now},
PurgeData : {type : Number, index : true}
});
var Packet = mongoose.model('Packet', packet);
var moment = require('moment');
//Schedule the event.
var event = {
name: 'purge',
collection: 'packet',
after: new Date(),
cron: "0 15 10 * * ?" //cron string representing a frequency - fire at 10:15am every day
};
scheduler.schedule(event)
scheduler.on('purge', function(packet, event) {
console.log(packet.PurgeData)
Packet.find({"PurgeData": {"$lt": 10} }, function (err, packets) {
packets.forEach(function (p){
var days_diff = moment().diff(moment(p.CreatedAt), 'days') // using momentjs library
Packet.update(
{
"_id": p._id
},
{
"$set": {
PurgeData: days_diff
}
}, function (err, doc){
console.log(doc);
});
});
});
Packet.find({"PurgeData": {"$gte": 10} }, function (err, packets) {
packets.forEach(function (p){
Packet.remove({ "_id": p._id }, function (err){
handleErr(err);
});
});
});
})