Complex query on more than one child in cloud functions - node.js

Question

Here is the structure of my firebase database:
/UserData
/DeviceMgmt
/Counters
/NumberOfAll:
/NumberOfSelected
/TotalDownloaded
...
/Devices
/pushId1
/uid
/signOutTime
/toSelect=true (optional)
/downloaded
/lastDownload
/pushId2
/pushId3
...
And this is my cloud function:
exports.markDevicesForDownload = functions.database.ref('/UserData/DeviceMgmt/Counters/NumberOfSelected').onUpdate( (change) => {
const changeRef = change.after.ref;
const deviceMgmtRef = changeRef.parent.parent; // /UserData/DeviceMgmt
if (change.after.val() === 0 ) { //NumberOfSelected gets 0 value
return deviceMgmtRef.once('value')
.then((snap) => {
const devicesRef = snap.child('Devices').ref;
var average;
var numberOfAllDevices;
var totalDownloaded;
numberOfAllDevices = snap.child('Counters/NumberOfAll').val();
totalDownloaded = snap.child('Counters/TotalDownloaded').val();
average = Math.round(totalDownloaded/numberOfAllDevices);
return devicesRef
.orderByChild('signOutTime')
.equalTo(0)
.once('value',(devices) => {
return devices.ref
.orderByChild('downloaded')
.endAt(average)
.once('value',(devices) => {
devices.forEach((device) => {
device.child('toSelect').ref.set(true);
});
});
});
});
} else {
return false;
}
});
The function triggers when the counter NumberOfSelected = 0;
This happens when under any of device pushId there is no child toSelect. Then the query on downloaded child makes all devices with downloaded less than average set toSelect=true.
I wanted to limit the devices only to those which have signOutTime equal 0.
Somehow that query does not work and all devices are considered.
What I did wrong???

Answer 1

I would push all async tasks into a promise array and then return them all when all tasks complete:
exports.markDevicesForDownload = functions.database.ref('/UserData/DeviceMgmt/Counters/NumberOfSelected').onUpdate((change) => {
const changeRef = change.after.ref;
const deviceMgmtRef = changeRef.parent.parent; // /UserData/DeviceMgmt
if (change.after.val() === 0) { //NumberOfSelected gets 0 value
return deviceMgmtRef.once('value')
.then((snap) => {
const promises = [];
const devicesRef = snap.child('Devices').ref;
var average;
var numberOfAllDevices;
var totalDownloaded;
numberOfAllDevices = snap.child('Counters/NumberOfAll').val();
totalDownloaded = snap.child('Counters/TotalDownloaded').val();
average = Math.round(totalDownloaded / numberOfAllDevices);
const dR = devicesRef
.orderByChild('signOutTime')
.equalTo(0)
.once('value', (devices) => {
const dW = devices.ref
.orderByChild('downloaded')
.endAt(average)
.once('value', (devices) => {
devices.forEach((device) => {
if (device.child("signOutTime").val() === 0){
promises.push(device.child('toSelect').ref.set(true));
}
});
});
promises.push(dW);
});
promises.push(dR);
return Promise.all(promises);
});
} else {
return false;
}
});