aggregate.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
 
//Database connection 
var uristring = 'mongodb://localhost/test';
var mongoOptions = { };
 
mongoose.connect(uristring, mongoOptions, function (err, res) {
    if (err) { 
        console.log('Error when connecting to: ' + uristring + '. ' + err);
    } 
    else {
        console.log('Successfully connected to: ' + uristring);
    }
});
 
 
//First let's create the Schemas:
// Record Schema
var Record = new Schema({
    amount: { type: Number, required: true },
    date: { type: Date, required: true },
    description: { type: String }
})
 
// Account Schema
var Account = new Schema({
    name: { type: String, required: true },
    currency: { type: String, required: true },
    created: { type: Date, default: Date.now },
    records: [Record]
});
 
//Define Models
var AccountModel = mongoose.model('Account', Account);
var RecordModel = mongoose.model('Record', Record);
var ObjectId = require('mongoose').Types.ObjectId;
 
// Utility functions to insert data:
var insertAccount = function(account, callback) {
	var Account = new AccountModel();
	Account.name = account.name;
	Account.currency = account.currency;
	Account.records = [];
 
	Account.save(function(err) {
		if (err) {
			console.log(err);
			return null;
		}
 
		return callback(Account._id);
	});
}
 
 
var insertRecords = function(accountId, record, numberOfRecords, callback) {
	AccountModel.findOne({_id:accountId}, function(err, account) {
		if (err) {
			console.log(err);
			return ;
		}
 
 		for (var i = 0; i < numberOfRecords; i++) {
			var Record = new RecordModel();
			Record.amount = record.amount;
			Record.date = new Date();
			Record.is_expense = record.is_expense;
	 
			account.records.push(Record);
		}
 
		account.save(function(err2) {
			if (err2) {
				console.log(err2);
			}

			return callback();
		});
	});
}
 
var listAccounts = function() {
	var query = AccountModel.find();
 
	query.exec(function(err, accounts) {
		if (err) {
			console.log(err);
		}
 
		console.log(accounts);
	});
}

var listAccount = function(id) {
	if (id == null) {
		return ;
	}

	var query = AccountModel.find({_id:id});
	query.field('_id name currency date');
 
	query.exec(function(err, accounts) {
		if (err) {
			console.log(err);
		}
 
		console.log(accounts);
	});
}
 
var removeAccount = function(accountId) {
	var query = AccountModel.findOne({_id:accountId});
 
	query.exec(function(err, account) {
		if (err) {
			console.log(err);
			return ;
		}
 
		account.remove();
	});
}

 
//Aggregation function
var getBalance = function(accountId) {
    AccountModel.aggregate([
        { $match: {
            _id: accountId
        }},
        { $unwind: "$records" },
        { $group: {
            _id: "$_id",
            balance: { $sum: "$records.amount"  }
        }}
    ], function (err, result) {
        if (err) {
            console.log(err);
            return;
        }
        console.log(result);
    });
}
 

//Let's add some data and call the getBalance fucntion
insertAccount({name:"First Account", currency: "Dollar"}, function(accountId) {
	if (accountId == null) {
		console.log("accountId is null");
		return ;
	}

	insertRecords(accountId, {amount:123.5}, 1000, function() {
		getBalance(accountId);
	});
});