Query data from firebase Array

Question

My firebase users tree has this structure:

users:

{
 {
 'userName': 'abc',
 'userEmail' : 'abc@abc.com',
 'userPreferences': 
   [ 
     0:'Cinema', 
     1:'It' 
   ] 
  },
  {
 'userName': 'abc',
 'userEmail' : 'abc@abc.com',
 'userPreferences': 
   [ 
     0:'Cinema', 
     1:'Music' 
   ] 
 }
 }

Then, I try to find all users that their preference list contain 'Cinema'.
I try this code:

var ref1 = new Firebase("https://event-application.firebaseio.com/users"); 
$scope.user = $firebaseArray(ref1.orderByChild("userpreferences").equalTo('Cinema'));
console.log($scope.user);

But I don't get the best result. I get this record:

What does *"I don't get the best solution"* means ? – Maen Apr 28 '16 at 10:59 — Maen, Apr 28 '16 at 10:59

score 1 · Answer 1 · answered Apr 28 '16 at 12:34

1

Your JSON structure shows preferences as userPreferences, so wouldn't the following work?

var ref1 = new Firebase("https://event-application.firebaseio.com/users"); 
$scope.user = $firebaseArray(ref1.orderByChild("userPreferences").equalTo('Cinema'));
console.log($scope.user);

However I think there is also another problem with your code, you're called an .equalTo('Cinema') however you're comparing it to an array, correct me if i'm wrong but I don't think the behaviour of .equalTo('Cinema') is to loop through each of the values and compare them, I think it's just a straight up comparison

If this is the case, you may need to build a custom query by reading the data from firebase and manipulating it via function available to a snapshot

answered Apr 28 '16 at 12:34

Grant

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6
24

Thank you for your answer. I edited my post. Yes that was my problem i don"t find how to compare .equalTo('Cinema') with array. And i must keep the same data structure – Sihem Hcine Apr 28 '16 at 16:22
@SihemHcine Would you like me to go into reading data from firebase? – Grant Apr 29 '16 at 08:08
yes of course Sir. Could you give me your mail please – Sihem Hcine Apr 29 '16 at 18:34

score 1 · Answer 2 · edited May 23 '17 at 12:34

In NoSQL you'll often end up with a data model that reflects the way your application uses the data. If you want to read all the users that have a preference for Cinema, you should model that in your tree:

users: {
   'uid-of-abc': {
     'userName': 'abc',
     'userEmail' : 'abc@abc.com',
     'userPreferences': [ 
        0:'Cinema', 
        1:'It' 
     ] 
   },
   'uid-of-def': {
     'userName': 'def',
     'userEmail' : 'abc@abc.com',
     'userPreferences': [ 
       0:'Cinema', 
       1:'Music' 
     ] 
   }
},
"preferences-lookup": {
  "Cinema": {
     "uid-of-abc": true,
     "uid-of-def": true
  },
  "It": {
     "uid-of-abc": true
  },
  "Music": {
     "uid-of-def": true
  }
}

Now you can find out what users prefer cinema with:

ref.child('preferences-lookup/Cinema').on('value', function(snapshot) {
  snapshot.forEach(function(userKey) {
    console.log(userKey.key()+' prefers Cinema');
  });
});

This is covered in this blog post on denormalizing data with Firebase, in the Firebase documentation on structuring data and in dozens of answers here on Stack Overflow. A few:

Thank you Sir for your anwer :). But in my application structure(code) i have not to define preference for Cinema. — Sihem Hcine, Apr 28 '16 at 16:20

Query data from firebase Array

2 Answers2