Using PUT to update a vote count

Question

I am making a simple full-stack javascript polls app using Yeoman's angular-fullstack generator. I have got to the point where I need to log user input to register a vote on an individual poll's answer.

Currently, my code affects the client-side code correctly, but doesn't update the database.

Here is the schema:

var PollSchema = new Schema({
    creator: String,
    title: String,
    answers: [{
        value: String,
        votes: Number
    }]
});

Here is the controller:

'use strict';

angular.module('angFullstackCssApp')
    .controller('ViewCtrl', function ($scope, $routeParams, $http) {
        $http.get('/api/polls/' + $routeParams._id).success(function (poll) {
            console.log(poll);
            $scope.poll = poll;
            $scope.radioData = {
                index: 0
            };

            $scope.submitForm = function () {
                console.log($scope.radioData.index);
                $scope.poll.answers[$scope.radioData.index].votes += 1;
                // Change database entry here
                $http.put('/api/polls/' + $routeParams._id, {answers: $scope.poll.answers});
            };
        });
    });

and here is the View:

<form ng-submit="submitForm()">

    <div ng-repeat="answer in poll.answers">
        <label><input type="radio" name="option" ng-model="radioData.index" value="{{$index}}"/>
            {{ answer.value }} - {{ answer.votes }} Votes
        </label>
    </div>
    <button class="btn btn-success" type="submit">Vote!</button>
</form>

In my terminal, I am getting a successful put request according to the ID I am passing in...

PUT /api/polls/56229ba4e10ae6ad29b7a493 200 3ms - 225b

...but nothing changes in my database. I get no console errors.

Here is my route:

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

and the update function (part of the yeoman default):

// Updates an existing poll in the DB.
exports.update = function(req, res) {
  if(req.body._id) { delete req.body._id; }
  Poll.findById(req.params.id, function (err, poll) {
    if (err) { return handleError(res, err); }
    if(!poll) { return res.status(404).send('Not Found'); }
    var updated = _.merge(poll, req.body);
    updated.save(function (err) {
      if (err) { return handleError(res, err); }
      return res.status(200).json(poll);
    });
  });
};

Edit: I've realised what's going on when a vote is submitted. When user clicks vote, a PUT request goes through to the server, and updates the value:

However, when the page is refreshed, it shows what has actually happened; all the values in the database have changed to the first answer value:

Still no console errors. If a value is selected and voted that isn't the first value, all the values change to the first regardless, but no votes are registered.

• How can I write a PUT request that successfully updates my database?