Using $firebase().$on('value', ...) does NOT work

I have 2 types of entities stored in Firebase, Cars and Users. Each car has a userID, which is the identity of the user who owns the car. I have a web page where I display data about the car, and I want to display the name of the car’s owner. This means that I need to sync both the car and the user name to the $scope, so I can display both sets of data on the same web page.

I was previously getting the car and user data using Firebase refs and once('value', ...) calls, which works just fine:

// get a Firebase reference to the car
var carRef = ref.child('cars').child($scope.carID);
// ...and bind the car to the $scope, so I can display it's data (not shown)

// now use the car's userID to look up the user's name, and bind it to the $scope
carRef.child('userID').once('value', function(userID) {
    // use the userID to look up the user, and bind her data to the $scope
    // (again not shown, but works just fine)
});

Now I’m trying to do the same thing using the new $firebase() API, which I’ve read about in the new API docs, angularFire-seed project, StackOverflow questions and even online tutorials. But it’s not working for me like it should:

var carRef = ref.child('cars').child($scope.carID);

// get a $firebase reference to the car
var $car = $firebase(carRef);

// now get the $car's userID, so we can look up the user
$car.$child('userID').$on('value', function(userID) {
    // this is never called!
});

Based on the firebase API documentation, calling $on('value', ...) should work just as well as calling on('value', ...) or once('value', ...) (as I did above). But the 'value' event’s callback is never called! If I change 'value' to 'loaded' then it does in fact work, but only the first time. If I view another car’s page (a different angular route) and then come back, it doesn’t work. Only if I do a full page refresh does the 'loaded' event’s callback get called again. Which actually makes complete sense, given the docs for loaded.

Anyway, why isn’t this working as expected?

Here are the versions I’m using:

• firebase.js 1.0.5
• firebase-simple-login.js 1.2.5
• angular.js 1.2.14
• angular-route.js 1.2.14
• angularfire.js 0.7.0

[katowulf]

Junk, that was incorrect. I think I took one too many bugs to the head this morning. (The $bind() method resolves with an unbind method, not $on).

So the correct usage would be as you stated it:

var callback = function(snap) {
   console.log(snap.val());
   ref.$off('value', callback);
};

ref.$on('value', callback);

[katowulf]

@romelgomez your comments have been deleted. This thread is over a year old, your comments were unrelated to the original question, and your comments were unrelated to AngularFire. If you want to discuss, reach out on firebase-talk or submit a new issue.