How to join denormalized data that are at a depth of 2+ in Firebase

Question

Here is the scenario: I have a list of topics, each topic includes posts, and each post is "liked" by a list of users. So my data looks something like this:

"topics": {
    "topic1": {
        "posts": {
            "post1": true,
            "post2": true
        }
     }
 },
 "posts": {
     "post1": {
         "title": "An awesome post",
         "likes": {
             "user1": true
         }
     },
     "post2": {
         "title": "An even better post",
         "likes": {
             "user1": true,
             "user2": true
         }
     }
 },
 "users": {
     "user1": {
         "name": "Mr. T",
         "email": "[e-mail]"
     },
     "user2": {
         "name": "Mr. Hello World",
         "email": "[e-mail]"
     }
 }

I (it seems, I) know how to get all posts on a topic using Firebase.util ( http://firebase.imtqy.com/firebase-util ):

Firebase.util.intersection(
    fb.child('topics').child('topic1').child('posts'),
    fb.child('posts')
)

But now I would like for each post to contain the names of the users who liked this post. How to do it?

Nothing will likely change, but it all happens in AngularFire.

Answer 1

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Firebase , - , , , .

HTML:

<h3>Normalizing user profiles into posts</h3>

<ul ng-controller="ctrl">
    <li ng-repeat="post in posts | orderByPriority" ng-init="user = users.$load(post.user)">
        {{user.name}}: {{post.title}}
    </li>
</ul>

JavaScript:

var app = angular.module('app', ['firebase']);
var fb = new Firebase(URL);

app.controller('ctrl', function ($scope, $firebase, userCache) {
    $scope.posts = $firebase(fb.child('posts'));
    $scope.users = userCache(fb.child('users'));
});

app.factory('userCache', function ($firebase) {
    return function (ref) {
        var cachedUsers = {};
        cachedUsers.$load = function (id) {
            if( !cachedUsers.hasOwnProperty(id) ) {
                cachedUsers[id] = $firebase(ref.child(id));
            }
            return cachedUsers[id];
        };
        cachedUsers.$dispose = function () {
            angular.forEach(cachedUsers, function (user) {
                user.$off();
            });
        };
        return cachedUsers;
    }
});