Is this the best way to retrieve an array with $firebase()? - angularjs

Question

I have arrays stored in Firebase, one of which I need to retrieve when a user logs in. Each user has their own array which requires authentication for read. (It would be inconvenient to switch to another data structure). Since $firebase() always returns an object, as per the docs, I'm using the orderByPriority filter. However, if I do simply
$scope.songs = $filter('orderByPriority')($firebase(myref));
that doesn't work as songs always get an empty array.
I don't understand why this happens, but what I've done to solve it is use the $firebase().$on('loaded',cb) form and applied the filter in the callback. Is this a good solution?
The drawback is that I cannot do $scope.songs.$save()
Here's my controller, including this solution:
.controller('songListController', function($scope, $rootScope, $firebase, $filter, $firebaseSimpleLogin){
var authRef = new Firebase('https://my-firebase.firebaseio.com/users'),
dataRef;
$scope.loginObj = $firebaseSimpleLogin(authRef);
$scope.songs = [];
$rootScope.$on("$firebaseSimpleLogin:login", function(event, user) {
// user authenticated with Firebase
dataRef = $firebase(authRef.child(user.id));
dataRef.$on('loaded', function(data){
$scope.songs = $filter('orderByPriority')(data);
});
});
//other controller methods go here
$scope.save = function(){
if (!$scope.loginObj.user)
{
alert('not logged in. login or join.');
return;
}
//Was hoping to do this
//$scope.songs.$save().then(function(error) {
//but having to do this instead:
dataRef.$set($scope.songs).then(function(error) {
if (error) {
alert('Data could not be saved.' + error);
} else {
alert('Data saved successfully.');
}
});
};
});
---Edit in response to Kato's answer---
This part of my app uses Firebase as a simple CRUD json store without any realtime aspects. I use $set to store changes, so I think I'm okay to use arrays. (I'm using jQueryUI's Sortable so that an HTML UL can be re-ordered with drag and drop, which seems to need an array).
I don't need realtime synchronisation with the server for this part of the app. I have a save button, which triggers the use of the $scope.save method above.

Answer 1

The problem with the approach above is that orderByPriority makes a single copy of the data. It's empty because $firebase hasn't finished retrieving results from the server yet.
If you were to wait for the loaded event, it would contain data:
var data = $firebase(myref);
data.$on('loaded', function() {
$scope.songs = $filter('orderByPriority')(data);
});
However, it's still not going to be synchronized. You'll need to watch for changes and update it after each change event (this happens automagically when you use orderByPriority as part of the DOM/view).
var data = $firebase(myref);
data.$on('change', function() {
$scope.songs = $filter('orderByPriority')(data);
});
Note that the 0.8 release will have a $asArray() which will work closer to what you want here. Additionally, you should avoid arrays most of the time.