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1

I have a Firebase structure like this:

user {
  uid {
    Lessons {
      lid1 {
         Title: ...
          }
      lid2 {
         Title: ...
          }
     }
   }
  }

I want to use AngularFire to convert user as array so I can filter them using Angular like this: 

var usersRef = new Firebase($rootScope.baseUrl + "users"); 
var userListfb = $firebase(usersRef).$asArray();

The problem is, I also need the number of child of the Lessons object. When I log the userListfb, it is an array. But inside the array, the Lessons node still an object. I can not user length to get its length. What is the correct way to find out the number of child of the Lessons Node with Firebase AngularFire?

Edit 1 According to Frank solution, I got an infinite loop (digest circle error from AngularJS). The problem is, I will not know the "uid" key. I need to loop it in the first array to get the uid into the second firebaseArray. Let's say I have a ng-repeat="user in users" in the view and call this on view level in each repeat:

{{getLessonLength(user.uid)}}

Then in the controller, I have this function:

$scope.users = $firebaseArray($scope.usersRef);

$scope.getLessonLength = function (uid) {

        var userRef = $rootScope.baseUrl + "users/" + uid + "/lessons/";

        var lessonsNode = $firebaseArray(new Firebase(userRef));

        return lessonsNode.length;
    }
}

And it throw this error: Error: [$rootScope:infdig] 10 $digest() iterations reached. Aborting! Watchers fired in the last 5 iterations: []

All I want it is something like var lessonsCount = snapshot.child('lessons').numChildren() in regular Firebase .on('child_added' ...), the numChildren() function in FirebaseArray. Please help!

share|improve this question
2  
AngularFire docs: "AngularFire is not a wrapper on the entire Firebase API with $ signs in front of the methods. It is also not ideal for synchronizing deeply nested collections inside of collections. But deeply nested collections should typically be avoided in distributed systems." – Kato Jan 27 at 20:25
    
@Kato So you suggestion I should not put the lessons object array inside the user array? So how should I flatten this structure in the Firebase way? I feel like nested array is so hard to avoid. Is there a different kind of thinking? Could you point me into the right direction? – Hugh Hou May 17 at 19:46

1 Answer 1

up vote 1 down vote accepted

AngularFire contains quite some code to ensure that an ordered collection in your Firebase maps correctly to a JavaScript array as Angular (and you) expect it.

If you have a reference to a specific user, you can just create a new sync ($firebase) and call $asArray on that.

var usersRef = new Firebase($rootScope.baseUrl + "users"); 
var userListfb = $firebase(usersRef).$asArray();
var uid1LessonsRef = userRef.child('uid1').child('Lessons');
var uid1LessonsArray = $firebase(uid1LessonsRef).$asArray();
uid1LessonsArray.$loaded().then(function(arr) {
    console.log('Loaded lessons, count: '+arr.length);
});

The data will only be synchronized once, no matter how many references you create to it.

share|improve this answer
    
But my problem is I need to connect the userListfb array to the Lesson array. I want the lessons number (the array length) and insert the value as a property inside the userListfb array. So I can use ng-repeat to go tho the userListfb array. When I try to use ng-repeat to get the uid number and call a function inside an expression like this {{calculateNum(list.uid)}}, the calculateNum will create an infinit loop error... I don't think it is ideal as well to let the loop open an new connection to firebase in each loop to just get the length of an inside object... – Hugh Hou Jan 27 at 1:31
    
Franks answer directly addresses your problem. You'll want to create a synchronized array for the lessons, specifically, if you expect them to appear in an array. – Kato Jan 27 at 20:26
1  
I want the lessons to be a nested array inside the user array. But firebase only return the first level array, lessons node is still an object... – Hugh Hou Jan 30 at 0:44
    
Also, could you clarify what you mean "The data will only be synchronized once, no matter how many references you create to it."? – Hugh Hou May 18 at 3:50

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