angular.js - updating sortorder in model from view - angularjs

Question

I have an Express Model/Controller, getting data from a mongoDB collection. One of the columns in this collection is sortOrder (which I use to display the entries in a specific order). To manage the data from this collection, I have an angular.js view with a table, listing these entries.
This table is constructed using ui-sortable, which allows me to drag-a-drop table rows, i.e. changing the display order. Up to this point everything works as expected.
Now, my question is: how do I get my model/controller to recognise these changes, and update the sortOrder column in the collection, to now show the new sorting order?
Here's the code of the view:
<section data-ng-controller="BusinessunitsController" data-ng-init="find()">
<div class="page-header">business units</div>
<table>
<thead>
<tr>
<th><i class="icon-fontawesome-webfont-141"></i></th>
<th>business unit name</th>
<th><i class="icon-fontawesome-webfont-241 right"></i></th>
</tr>
</thead>
<tbody ui-sortable ng-model="businessunits">
<tr data-ng-repeat="businessunit in businessunits">
<td class="draggable">{{businessunit.sortOrder}}</td>
<td style="color:{{businessunit.color}}">{{businessunit.name}}</td>
<td>
<a data-ng-href="#!/businessunits/{{businessunit._id}}"><i class="icon-fontawesome-webfont-65"></i></a>
<a data-ng-href="#!/businessunits/{{businessunit._id}}"><i class="icon-fontawesome-webfont-240 alert"></i></a>
</td>
</tr>
</tbody>
</table>
</section>
Angular controller:
'use strict';
// Businessunits controller
angular.module('businessunits').controller('BusinessunitsController', ['$scope', '$stateParams', '$location', 'Authentication', 'Businessunits',
function($scope, $stateParams, $location, Authentication, Businessunits) {
$scope.authentication = Authentication;
// Create new Businessunit
$scope.create = function() {
// Create new Businessunit object
var businessunit = new Businessunits({
name: this.name,
color: this.color,
sortOrder: this.sortOrder
});
// Redirect after save
businessunit.$save(function(response) {
$location.path('businessunits/' + response._id);
});
// Clear form fields
this.name = '';
};
// Remove existing Businessunit
$scope.remove = function(businessunit) {
if (businessunit) {
businessunit.$remove();
for (var i in $scope.businessunits) {
if ($scope.businessunits[i] === businessunit) {
$scope.businessunits.splice(i, 1);
}
}
} else {
$scope.businessunit.$remove(function() {
$location.path('businessunits');
});
}
};
// Update existing Businessunit
$scope.update = function() {
var businessunit = $scope.businessunit;
businessunit.$update(function() {
$location.path('businessunits/' + businessunit._id);
});
};
// Find a list of Businessunits
$scope.find = function() {
Businessunits.query(function(businessunits) {
$scope.businessunits = businessunits;
});
};
// Find existing Businessunit
$scope.findOne = function() {
Businessunits.get({
businessunitId: $stateParams.businessunitId
}, function(businessunit) {
$scope.businessunit = businessunit;
});
};
}
]);
Express controller:
'use strict';
/**
* Module dependencies.
*/
var mongoose = require('mongoose'),
Businessunit = mongoose.model('Businessunit'),
_ = require('lodash');
/**
* Create a Businessunit
*/
exports.create = function(req, res) {
var businessunit = new Businessunit(req.body);
businessunit.user = req.user;
businessunit.save(function(err) {
if (err) {
return res.send('users/signup', {
errors: err.errors,
businessunit: businessunit
});
} else {
res.jsonp(businessunit);
}
});
};
/**
* Show the current Businessunit
*/
exports.read = function(req, res) {
res.jsonp(req.businessunit);
};
/**
* Update a Businessunit
*/
exports.update = function(req, res) {
var businessunit = req.businessunit;
businessunit = _.extend(businessunit, req.body);
businessunit.save(function(err) {
if (err) {
res.render('error', {
status: 500
});
} else {
res.jsonp(businessunit);
}
});
};
/**
* Delete an Businessunit
*/
exports.delete = function(req, res) {
var businessunit = req.businessunit;
businessunit.remove(function(err) {
if (err) {
res.render('error', {
status: 500
});
} else {
res.jsonp(businessunit);
}
});
};
/**
* List of Businessunits
*/
exports.list = function(req, res) {
Businessunit.find().sort('sortOrder').populate('user', 'name').exec(function(err, businessunits) {
if (err) {
res.render('error', {
status: 500
});
} else {
res.jsonp(businessunits);
}
});
};
/**
* Businessunit middleware
*/
exports.businessunitByID = function(req, res, next, id) {
Businessunit.findById(id).populate('user', 'name').exec(function(err, businessunit) {
if (err) return next(err);
if (!businessunit) return next(new Error('Failed to load Businessunit ' + id));
req.businessunit = businessunit;
next();
});
};
/**
* Businessunit authorization middleware
*/
exports.hasAuthorization = function(req, res, next) {
if (req.businessunit.user.id !== req.user.id) {
return res.send(403, 'User is not authorized');
}
next();
};