firebase sort reverse order

Question

var playersRef = firebase.database().ref(\"team_mapping/\");


playersRef.orderByChild(\"score\").limitToFirst(7).on(\"child_added\", function(data) {
}


        

Answer 1

just use reverse() on the array , suppose if you are storing the values to an array items[] then do a this.items.reverse()

ref.subscribe(snapshots => {
       this.items = [];
      snapshots.forEach(snapshot => {

        this.items.push(snapshot);

      });
      **this.items.reverse();**
    },

Answer 2

You can limit to the last 7 which will give you the highest scores since the query is in ascending order. Then all you have to do is reverse the last 7 you get for them to be in descending order.

var playersRef = firebase.database().ref("team_mapping/");
var playersData = [];
var pageCursor;

playersRef.orderByChild("score").limitToLast(7).on("child_added", function(data) {
    playersData = [data] + playersData;
}

UPDATE

Here is an example of how you could paginate by score.

const query = firebase.database().ref("team_mappings").orderByChild('score');

var snapshots = [];

function reversedChildren(snapshot) {
    var children = [];
    snapshot.forEach(function (child) { children.unshift(child); });
    return children;
}

function addPlayerToLeaderBoard(snapshot) {
    var key = snapshot.key;
    var place = snapshots.indexOf(snapshot) + 1;
    var score = snapshot.child('score').val();
    $('#leaderboard').append(`<li><b>${key}: ${score}</li>`);
}

function parsePage(snapshot) {
    var children = reversedChildren(snapshot);
    children.forEach(function (child) {
        players.push(child);
        addPlayerToLeaderBoard(child);
    });
    pageCursor = children[children.length - 1];
}

function reloadPlayers() {
    players = [];
    pageCursor = null;
    query.limitToLast(5).once('value').then(parsePage);
}

function loadMorePlayers() {
    query.endAt(pageCursor).limitToLast(5).once('value').then(parsePage);
}

reloadPlayers();

$('#reload').on('click', reloadPlayers);
$('#load_more').on('click', loadMorePlayers);

Answer 3

Unfortunatelly, there is not a shortcut for this yet. However, if you are using Listview or Recyclerview as UI, you could simply solve this issue by reversing the UI,by reversing Listview or Recyclerview

For Recyclerview you could reverse as follows:

LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setReverseLayout(true);
layoutManager.setStackFromEnd(true);
recyclerView.setLayoutManager(layoutManager)

For Listview:

listView.setStackFromBottom(true);