Unable to update an object inside MongoDB collection using HTTP Put?

I am new to AngularJS and I was trying to update my MongoDB Database. I am having an issue when I am trying to update an object inside my collection. The following is my attempt at trying to do so:

//listviewFactory is already injected and returns an event object
//I call $scope.put when clicking (ng-click) on a button

$scope.event = listviewFactory.getEvent();

$scope.put = function(event){
    var currentUser = {};
    if($cookieStore.get('token')) {
        currentUser = User.get();
    }

    event.attendees.push(currentUser);

    $http.post('/api/events/' + event._id, event).success(function(data){
      for(var i = 0; i < event.attendees.length; i++){
        console.log("Attendees: ", event.attendees[i]);
      }

      $location.path('/');
    });

};

I'm just unsure of why my code isn't working. When I do the $http put request, my function is successful and proceeds to perform the console.log. When I print out the attendees array, I saw that the currentUser object is indeed appended to my event.attendees array. However, when I check my database using the Mongo shell, My attendees array is not updated and remains blank. Any ideas on why or where I may be wrong at? Below is also my server side code in how I am routing my application and specifying how to store the information in MongoDB.

module.exports = function(app) {
  app.use('/api/events', require('./api/event'));
  ...
}

module.exports = mongoose.model('Event', EventSchema);
    var express = require('express');
    var controller = require('./event.controller');

    var router = express.Router();

router.get('/', controller.index);
router.put('/:id', controller.update);

// Updates an existing event in the DB.
exports.update = function(req, res) {
  if(req.body._id) { delete req.body._id; }
  Event.findById(req.params.id, function (err, event) {
    if (err) { return handleError(err); }
    if(!event) { return res.send(404); }
    var updated = _.merge(event, req.body);
    updated.save(function (err) {
      if (err) { return handleError(err); }
      return res.json(200, event);
    });
  });
};

EDIT: When I console.log currentUser:

Current User:  
Resource {$promise: Object, $resolved: false, $get: function, $save: function, $query: function…}
$promise: Object
$resolved: true
__v: 0
_id: "53dd72fb5a24aa781a3cbde8"
email: "test@test.com"
name: "Test User"
provider: "local"
role: "user"

EDIT: Mongoose schema:

'use strict';

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;

var EventSchema = new Schema({
    startDate: Date,
    endDate: Date,
    eventLocation: String,
    eventName: String,
    attendees: Array
});