具有Firebase云功能的排行榜

Question

My current database structure looks like this,

Which basically has a mobile_users table and and a top 100 table which will be the leaderboard.

Im trying to figure out how to write a cloud function that executes every minute that updates/populates the top100 table with the userid, earned_points from mobile_users and sort it by earned_points.

Should i add a rank field on this table or is there a way to order the table from asc/desc order based on mobile_users?

My current function looks like this

exports.dbRefOnWriteEvent = functions.database.ref('/mobile_user/{userId}/{earned_points}').onWrite(event => {
    var ref = admin.database().ref("/top100");
    ref.orderByChild("earned_points").once("value", function(dataSnapshot) {
        var i = 0;
        dataSnapshot.forEach(function(childSnapshot) {
          var r = (dataSnapshot.numChildren() - i);
          childSnapshot.ref.update({rank: r},function(error) {
              if (error != null)
                console.log("update error: " + error);
          });
          i++;
        });
    });
});

I have yet to figure out how to tell the cloud function to execute every minute. I am having trouble structuring these type of queries.

My function is also failing to populate the the top100 table with those 3 current users. I would appreciate if someone could point me in the right direction.

Answer 1

Create a http request function that will do your business.

Then use cron-job to call your http firebase function every minute : cron-job

Answer 2

Maybe you can have two root nodes in your database. One like the above and a second node that is called leaderboard.

That second node can be an array where the index reflects the rank and the name reflects the score.

Leaderboard
           |-- [0] 
                |-- score: 5000
                |-- uid: 4zzdawqeasdasq2w1
           |---[1]
                |-- score: 4990
                |-- uid: 889asdas1891sadaw

Then when you get a new score, you update the user's node and then also update the leaderboard. Then you just grab the uid and look up the name from the user's node.

Like the other posters said, use a HTTP Firebase Cloud Function and a chron job.

However I would recommend you use a chron job just to keep the cloud function alive (look up cold start firebase functions), but also make a fetch request to trigger the cloud function from the front-end everytime a user plays the game and generates a score. Otherwise if you get 10 plays per minute and it only updates once a minute, that will not be great user experience for the players who expect a real time leaderboard.