Get sorted list of objects in Firebase based on child value

Question

I have JSON data coming from a Real-time Firebase Database that I want to order so that I get the trips with the lowest/highest timestamp. I'm using the queryOrdered(byChild:) method:

class APICardService: NSObject {
    class func fetchTrips(forID userID: String, completion: @escaping ([Trip]) -> Void) {
        guard let userID = APIAuthService.getUserID() else { return }
        let path = "users/\(userID)/trips"
        print("fetch trips path", path)
        Database.database().reference().child(path).queryOrdered(byChild: "timestamp").observe(.value) { (snapshot) in
            var trips = [Trip]()
            if let dictionary = snapshot.value as? [String: Any] {
                print("DICTIONARY coming in", dictionary) // I've posted the data below
                for (key, value) in dictionary {
                    if let dict = value as? [String: Any] {
                        let trip = Trip(key: key, dbValues: dict)
                        trips.append(trip)
                    }
                }
            }
            completion(trips)
        }
    }
}

But objects are not coming out with the lowest/highest timestamp first (I think the query child doesn't do anything actually). Any hints?

Yes, I can use the Swift sort built-in function but I'd prefer to just get the right query with Firebase the first time.

["-L4kDSCyapSI9ZXTKPAg": {
    address = "Telangana, India";
    imageURL = "https://firebasestorage.googleapis.com/v0/b/indiana-f5501.appspot.com/o/tripsImages%2FqMBqd7Xa7BW7sr8TRIsELdAjEnr1%2Ftrips_images%2FDC1F3B1D-C063-4A1B-A389-AD2271D33A26.jpg?alt=media&token=b78c9d12-f1d8-463c-bca7-6a968c60ab53";
    latitude = "18.1124372";
    longitude = "79.01929969999999";
    placeID = "ChIJQ-0plNtQMzoRWUBZQad772M";
    timestamp = 2;
    title = Telangana;
    }, "-L4k2GYfCa5fUSu0B5K3": {
        address = "Istanbul, Turkey";
        imageURL = "https://firebasestorage.googleapis.com/v0/b/indiana-f5501.appspot.com/o/tripsImages%2FqMBqd7Xa7BW7sr8TRIsELdAjEnr1%2Ftrips_images%2F4C8DA002-9F60-4178-A6E8-56150832B260.jpg?alt=media&token=368294f2-86b1-449d-8c36-69f52e6af0c3";
        latitude = "41.0082376";
        longitude = "28.9783589";
        placeID = "ChIJawhoAASnyhQR0LABvJj-zOE";
        timestamp = 4;
        title = Istanbul;
    }, "-L4k29yUm3k_4s0UIGN7": {
        address = "Milan, Metropolitan City of Milan, Italy";
        imageURL = "https://firebasestorage.googleapis.com/v0/b/indiana-f5501.appspot.com/o/tripsImages%2FqMBqd7Xa7BW7sr8TRIsELdAjEnr1%2Ftrips_images%2FD4923507-D9B2-45E2-A7DD-7E04C8786FE7.jpg?alt=media&token=ccf4a972-733c-40d0-87e9-2d557e6fdfe0";
        latitude = "45.4642035";
        longitude = "9.189982000000001";
        placeID = "ChIJ53USP0nBhkcRjQ50xhPN_zw";
        timestamp = 5;
        title = Milan;
    }, "-L4k2DV1wy34cLRRMyBz": {
        address = "San Francisco, CA, USA";
        imageURL = "https://firebasestorage.googleapis.com/v0/b/indiana-f5501.appspot.com/o/tripsImages%2FqMBqd7Xa7BW7sr8TRIsELdAjEnr1%2Ftrips_images%2F9C624C94-16D1-49BC-A27E-126FFD25DF41.jpg?alt=media&token=78cb4e15-12b2-403a-b0a5-ec2b997612a1";
        latitude = "37.7749295";
        longitude = "-122.4194155";
        placeID = "ChIJIQBpAG2ahYAR_6128GcTUEo";
        timestamp = 4000;
        title = "San Francisco";
    }, "-L4kBUuRlsaUm3Eve7K5": {
        address = "27100 Pavia, Province of Pavia, Italy";
        imageURL = "https://firebasestorage.googleapis.com/v0/b/indiana-f5501.appspot.com/o/tripsImages%2FqMBqd7Xa7BW7sr8TRIsELdAjEnr1%2Ftrips_images%2F70F95915-59CD-4E30-939D-3D954598CE6A.jpg?alt=media&token=54af1b0e-638c-4082-9383-525e3acb505a";
        latitude = "45.1847248";
        longitude = "9.1582069";
        placeID = ChIJSQD6dUwmh0cRjoLPs7y0tfU;
        timestamp = 1;
        title = Pavia;
    }]

@PrashantTukadiya yeah but then Firebase wouldn't know which value to use for sorting because you didn't specify it — Cesare, Feb 07 '18 at 12:58
The code you shared doesn't do anything with the data yet, which may well be where the problems is. Please update your question to show the minimal code that actually uses the data and shows the problem. A simple example of this can be to log the data. — Frank van Puffelen, Feb 07 '18 at 15:27
Thanks @FrankvanPuffelen, it's nice to hear from a Googler who is part of the Firebase team. Just updated my question. Hope that's enough. — Cesare, Feb 07 '18 at 15:44
As soon as you call `snapshot.value as? [String: Any]`, the data is converted to a dictionary which doesn't have an order anymore. To ensure you keep the order of the children, loop over `snapshot.children` and only call `.value` on each child. Also see my answer here: https://stackoverflow.com/questions/40166483/firebase-getting-data-in-order/40168370#40168370 — Frank van Puffelen, Feb 07 '18 at 16:10

Get sorted list of objects in Firebase based on child value

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