Firebase queryOrderedByChild() method not giving sorted data

Question

My database structure is some thing like this:

{
  "users": {
    "alovelace": {
      "name": "Ada Lovelace",
      "score": 4,
    },
    "ghopper": { ... },
    "eclarke": { ... }
  }
}

I am trying to retrieve top 20 scores in descending order.

let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToLast(20)
queryRef.observeSingleEventOfType(.Value, withBlock: { (querySnapShot) in
      print(querySnapShot.value)
})

i am trying to get output like

score": 4
score": 3
score": 2

or 

score": 2
score": 3
score": 4

or 

2
3
4

Please let me know how to solve this.

Answer 1

Use method observeEventType instead of observeSingleEventOfType. Also, make FIRDataEventType to ChildAdded.

Last, If you want Top 20 items, use queryLimitedToFirst instead of queryLimitedToLast.

{
  "users" : {
    "alovelace" : {
      "name" : "Ada Lovelace",
      "score" : 4
    },
    "eclarke" : {
      "name" : "Emily Clarke",
      "score" : 5
    },
    "ghopper" : {
      "name" : "Grace Hopper",
      "score" : 2
    }
  }
}

For the dataset above

let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded, withBlock: { (snapshot) in
    print("key: \(snapshot.key), value: \(snapshot.value)")
})

key: ghopper, value: Optional({ name = Grace Hopper; score = 2; })

key: alovelace, value: Optional({ name = Ada Lovelace; score = 4; })

key: eclarke, value: Optional({ name = Emily Clarke; score = 5; })

Snapshot will returns the contents as native types. Data types returned:

• NSDictionary
• NSArray
• NSNumber (also includes booleans)
• NSString

So, you can get your scores this way.

    let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded, withBlock: { (snapshot) in
    if let scores = snapshot.value as? NSDictionary {
        print(scores["score"])
    }
})

Optional(2)

Optional(4)

Optional(5)

Moreover, the default of realtime database return everything in ascending order.

If you want descending order, you can make some tricks(4:40) in your database.