I am working on a game app using React native and Matter.js.
I am trying to implement a system that adds points every time a bullet hits a target.
In order to do this, I am trying to use collisionStart to detect the collision.
However, even though the bullet and target collide only once, the event seems to be triggered 41 times.
This is the code:
Matter.Events.on(engine, 'collisionStart', (event) => {
let pairs = event.pairs
for (const pair of pairs) {
if (pair.bodyA.label === 'bullet' && pair.bodyB.label === 'Worm') {
console.log("target hit");
}
}
})
In the end, I'm planning to replace console.log with something that adds points. At the current moment, one collision seems like it would trigger the add points 41 times, which is obviously not ideal.
Any ideas what is happening here and how I can get this to trigger only once for one collision?
Try next example. I take it from my own project [you need little adaptd from ts to js]:
Matter.Events.on(this.starter.getEngine(), "collisionStart", function (event) {
root.collisionCheck(event, true);
});
public collisionCheck(event, ground: boolean) {
const myInstance = this;
const pairs = event.pairs;
for (let i = 0, j = pairs.length; i !== j; ++i) {
const pair = pairs[i];
if (pair.activeContacts) {
if (pair.bodyA.label === "bullet" && pair.bodyB.label === "Worm") {
const collectitem = pair.bodyA;
this.playerDie(collectitem);
} else if (pair.bodyB.label === "bullet" && pair.bodyA.label === "Worm") {
const collectitem = pair.bodyB;
this.playerDie(collectitem);
}
// ....
}
}
}
public destroyBody = (destroyBody) => {
try {
Matter.Composite.remove(this.getWorld(), destroyBody);
} catch(err) {
console.log(err)
}
}
If you still have same problem , we can adapt also with flag PREVENT_DOUBLE_BY_1_SECOUND for example.
I want to sort an array, using Web Workers. But this array might receive new values over time, while the worker is still performing the sort function.
So my question is, how can I "stop" the sorting computation on the worker after receiving the new item, so it can perform the sort on the array with that item, while still keeping the sorting that was already made?
Example:
let worker = new Worker('worker.js');
let list = [10,1,5,2,14,3];
worker.postMessage({ list });
setInterval(() => worker.postMessage({ num: SOME_RANDOM_NUM, list }), 100);
worker.onmessage = event => {
list = event.data.list;
}
So lets say that, I've passed 50, the worker made some progress in the sorting before that and now I have something like this:
[1, 2, 3, 10, 5, 14, 50]. Which means the sorting stopped at index 3. So I pass this new array back to the worker, so it can continue the sorting from position 3.
How can I accomplish that, since there is no way to pause/resume a web worker?
Even though the Worker works on an other thread than the one of your main page, and can thus run continuously without blocking the UI, it still runs on a single thread.
This means that until your sort algorithm has finished, the Worker will delay the execution of the message event handler; it is as blocked as would be the main thread.
Even if you made use of an other Worker from inside this worker, the problem would be the same.
The only solution would be to use a kind of generator function as the sorter, and to yield it every now and then so that the events can get executed.
But doing this will drastically slow down your sorting algorithm.
To make it better, you could try to hook to each Event Loop, thanks to a MessageChannel object: you talk in one port and receive the message in the next Event loop. If you talk again to the other port, then you have your own hook to each Event loop.
Now, the best would be to run a good batch in every of these Event loop, but for demo, I'll call only one instance of our generator function (that I borrowed from this Q/A)
const worker = new Worker(getWorkerURL());
worker.onmessage = draw;
onclick = e => worker.postMessage(0x0000FF/0xFFFFFF); // add a red pixel
// every frame we request the current state from Worker
function requestFrame() {
worker.postMessage('gimme a frame');
requestAnimationFrame(requestFrame);
}
requestFrame();
// drawing part
const ctx = canvas.getContext('2d');
const img = ctx.createImageData(50, 50);
const data = new Uint32Array(img.data.buffer);
ctx.imageSmoothingEnabled = false;
function draw(evt) {
// converts 0&1 to black and white pixels
const list = evt.data;
list.forEach((bool, i) =>
data[i] = (bool * 0xFFFFFF) + 0xFF000000
);
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.putImageData(img,0,0);
// draw bigger
ctx.scale(5,5);
ctx.drawImage(canvas, 0,0);
}
function getWorkerURL() {
const script = document.querySelector('[type="worker-script"]');
const blob = new Blob([script.textContent]);
return URL.createObjectURL(blob);
}
body{
background: ivory;
}
<script type="worker-script">
// our list
const list = Array.from({length: 2500}).map(_=>+(Math.random()>.5));
// our sorter generator
let sorter = bubbleSort(list);
let done = false;
/* inner messaging channel */
const msg_channel = new MessageChannel();
// Hook to every Event loop
msg_channel.port2.onmessage = e => {
// procede next step in sorting algo
// could be a few thousands in a loop
const state = sorter.next();
// while running
if(!state.done) {
msg_channel.port1.postMessage('');
done = false;
}
else {
done = true;
}
}
msg_channel.port1.postMessage("");
/* outer messaging channel (from main) */
self.onmessage = e => {
if(e.data === "gimme a frame") {
self.postMessage(list);
}
else {
list.push(e.data);
if(done) { // restart the sorter
sorter = bubbleSort(list);
msg_channel.port1.postMessage('');
}
}
};
function* bubbleSort(a) { // * is magic
var swapped;
do {
swapped = false;
for (var i = 0; i < a.length - 1; i++) {
if (a[i] > a[i + 1]) {
var temp = a[i];
a[i] = a[i + 1];
a[i + 1] = temp;
swapped = true;
yield swapped; // pause here
}
}
} while (swapped);
}
</script>
<pre> click to add red pixels</pre>
<canvas id="canvas" width="250" height="250"></canvas>
Note that the same can be achieved with an async function, which may be more practical in some cases:
const worker = new Worker(getWorkerURL());
worker.onmessage = draw;
onclick = e => worker.postMessage(0x0000FF/0xFFFFFF); // add a red pixel
// every frame we request the current state from Worker
function requestFrame() {
worker.postMessage('gimme a frame');
requestAnimationFrame(requestFrame);
}
requestFrame();
// drawing part
const ctx = canvas.getContext('2d');
const img = ctx.createImageData(50, 50);
const data = new Uint32Array(img.data.buffer);
ctx.imageSmoothingEnabled = false;
function draw(evt) {
// converts 0&1 to black and white pixels
const list = evt.data;
list.forEach((bool, i) =>
data[i] = (bool * 0xFFFFFF) + 0xFF000000
);
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.putImageData(img,0,0);
// draw bigger
ctx.scale(5,5);
ctx.drawImage(canvas, 0,0);
}
function getWorkerURL() {
const script = document.querySelector('[type="worker-script"]');
const blob = new Blob([script.textContent]);
return URL.createObjectURL(blob);
}
body{
background: ivory;
}
<script type="worker-script">
// our list
const list = Array.from({length: 2500}).map(_=>+(Math.random()>.5));
// our sorter generator
let done = false;
/* outer messaging channel (from main) */
self.onmessage = e => {
if(e.data === "gimme a frame") {
self.postMessage(list);
}
else {
list.push(e.data);
if(done) { // restart the sorter
bubbleSort(list);
}
}
};
async function bubbleSort(a) { // async is magic
var swapped;
do {
swapped = false;
for (var i = 0; i < a.length - 1; i++) {
if (a[i] > a[i + 1]) {
const temp = a[i];
a[i] = a[i + 1];
a[i + 1] = temp;
swapped = true;
}
if( i % 50 === 0 ) { // by batches of 50?
await waitNextTask(); // pause here
}
}
} while (swapped);
done = true;
}
function waitNextTask() {
return new Promise( (resolve) => {
const channel = waitNextTask.channel ||= new MessageChannel();
channel.port1.addEventListener("message", (evt) => resolve(), { once: true });
channel.port2.postMessage("");
channel.port1.start();
});
}
bubbleSort(list);
</script>
<pre> click to add red pixels</pre>
<canvas id="canvas" width="250" height="250"></canvas>
There are two decent options.
Option 1: Worker.terminate()
The first is just to kill your existing web worker and start a new one. For that you can use Worker.terminate().
The terminate() method of the Worker interface immediately terminates the Worker. This does not offer the worker an opportunity to finish its operations; it is simply stopped at once.
The only downsides of this approach are:
You lose all worker state. If you had to copy a load of data into it for the request you have to do it all again.
It involves thread creation and destruction, which isn't as slow as most people think but if you terminate web workers a lot it might cause issues.
If neither of those are an issue it is probably the easiest option.
In my case I have lots of state. My worker is rendering part of an image, and when the user pans to a different area I want it to stop what it is doing and start rendering the new area. But the data needed to render the image is pretty huge.
In your case you have the state of your (presumably huge) list that you don't want to use.
Option 2: Yielding
The second option is basically to do cooperative multitasking. You run your computation as normal, but every now and then you pause (yield) and say "should I stop?", like this (this is for some nonsense calculation, not sorting).
let requestId = 0;
onmessage = event => {
++requestId;
sortAndSendData(requestId, event.data);
}
function sortAndSendData(thisRequestId, data) {
let isSorted = false;
let total = 0;
while (data !== 0) {
// Do a little bit of computation.
total += data;
--data;
// Check if we are still the current request ID.
if (thisRequestId !== requestId) {
// Data was changed. Cancel this sort.
return;
}
}
postMessage(total);
}
This won't work though because sortAndSendData() runs to completion and blocks the web worker's event loop. We need some way to yield just before thisRequestId !== requestId. Unfortunately Javascript doesn't quite have a yield method. It does have async/await so we might try this:
let requestId = 0;
onmessage = event => {
console.log("Got event", event);
++requestId;
sortAndSendData(requestId, event.data);
}
async function sortAndSendData(thisRequestId, data) {
let isSorted = false;
let total = 0;
while (data !== 0) {
// Do a little bit of computation.
total += data;
--data;
await Promise.resolve();
// Check if we are still the current request ID.
if (thisRequestId !== requestId) {
console.log("Cancelled!");
// Data was changed. Cancel this sort.
return;
}
}
postMessage(total);
}
Unfortunately it doesn't work. I think it's because async/await executes things eagerly using "microtasks", which get executed before pending "macrotasks" (our web worker message) if possible.
We need to force our await to become a macrotask, which you can do using setTimeout(0):
let requestId = 0;
onmessage = event => {
console.log("Got event", event);
++requestId;
sortAndSendData(requestId, event.data);
}
function yieldToMacrotasks() {
return new Promise((resolve) => setTimeout(resolve));
}
async function sortAndSendData(thisRequestId, data) {
let isSorted = false;
let total = 0;
while (data !== 0) {
// Do a little bit of computation.
total += data;
--data;
await yieldToMacrotasks();
// Check if we are still the current request ID.
if (thisRequestId !== requestId) {
console.log("Cancelled!");
// Data was changed. Cancel this sort.
return;
}
}
postMessage(total);
}
This works! However it is extremely slow. await yieldToMacrotasks() takes approximately 4 ms on my machine with Chrome! This is because browsers set a minimum timeout on setTimeout(0) of something like 1 or 4 ms (the actual minimum seems to be complicated).
Fortunately another user pointed me to a quicker way. Basically sending a message on another MessageChannel also yields to the event loop, but isn't subject to the minimum delay like setTimeout(0) is. This code works and each loop only takes ~0.04 ms which should be fine.
let currentTask = {
cancelled: false,
}
onmessage = event => {
currentTask.cancelled = true;
currentTask = {
cancelled: false,
};
performComputation(currentTask, event.data);
}
async function performComputation(task, data) {
let total = 0;
let promiseResolver;
const channel = new MessageChannel();
channel.port2.onmessage = event => {
promiseResolver();
};
while (data !== 0) {
// Do a little bit of computation.
total += data;
--data;
// Yield to the event loop.
const promise = new Promise(resolve => {
promiseResolver = resolve;
});
channel.port1.postMessage(null);
await promise;
// Check if this task has been superceded by another one.
if (task.cancelled) {
return;
}
}
// Return the result.
postMessage(total);
}
I'm not totally happy about it - it relies on postMessage() events being processed in FIFO order, which I doubt is guaranteed. I suspect you could rewrite the code to make it work even if that isn't true.
You can do it with some trick – with the help of setTimeout function interrupting. For example it is not possible without an addition thread to execute 2 functions parallel, but with setTimeout function interrupting trick we can do it like follows:
Example of parallel execution of functions
var count_0 = 0,
count_1 = 0;
function func_0()
{
if(count_0 < 3)
setTimeout(func_0, 0);//the same: setTimeout(func_0);
console.log('count_0 = '+count_0);
count_0++
}
function func_1()
{
if(count_1 < 3)
setTimeout(func_1, 0);
console.log('count_1 = '+count_1)
count_1++
}
func_0();
func_1();
You will get this output:
count_0 = 0
count_1 = 0
count_0 = 1
count_1 = 1
count_0 = 2
count_1 = 2
count_0 = 3
count_1 = 3
Why is it possible? Because the setTimeout function needs some time to be executed. And this time is even enought for the execution of some part from your following code.
Solution for you
For this case you have to write your own array sort function (or you can also use the following function from me) because we can not interrupt the native sort function. And in this your own function you have to use this setTimeout function interrupting trick. And you can receive your message event notification.
In the following example I have the interrupting in the half length of my array, and you can change it if you want.
Example with custom sort function interrupting
var numbers = [4, 2, 1, 3, 5];
// this is my bubble sort function with interruption
/**
* Sorting an array. You will get the same, but sorted array.
* #param {array[]} arr – array to sort
* #param {number} dir – if dir = -1 you will get an array like [5,4,3,2,1]
* and if dir = 1 in opposite direction like [1,2,3,4,5]
* #param {number} passCount – it is used only for setTimeout interrupting trick.
*/
function sortNumbersWithInterruption(arr, dir, passCount)
{
var passes = passCount || arr.length,
halfOfArrayLength = (arr.length / 2) | 0; // for ex. 2.5 | 0 = 2
// Why we need while loop: some values are on
// the end of array and we have to change their
// positions until they move to the first place of array.
while(passes--)
{
if(!passCount && passes == halfOfArrayLength)
{
// if you want you can also not write the following line for full break of sorting
setTimeout(function(){sortNumbersWithInterruption(arr, dir, passes)}, 0);
/*
You can do here all what you want. Place 1
*/
break
}
for(var i = 0; i < arr.length - 1; i++)
{
var a = arr[i],
b = arr[i+1];
if((a - b) * dir > 0)
{
arr[i] = b;
arr[i+1] = a;
}
}
console.log('array is: ' + arr.join());
}
if(passCount)
console.log('END sring is: ' + arr.join());
}
sortNumbersWithInterruption(numbers, -1); //without passCount parameter
/*
You can do here all what you want. Place 2
*/
console.log('The execution is here now!');
You will get this output:
array is: 4,2,3,5,1
array is: 4,3,5,2,1
The execution is here now!
array is: 4,5,3,2,1
array is: 5,4,3,2,1
END sring is: 5,4,3,2,1
You can do it with insertion sort (kind of).
Here is the idea:
Start your worker with an internal empty array (empty array is sorted obviously)
Your worker receives only elements not the entire array
Your worker insert any received element right in correct position into the array
Every n seconds, the worker raises a message with the current array if it has changed after the last event. (If you prefer, you can send the array on every insertion, but is more efficient to buffer somehow)
Eventually, you get the entire array, if any item is added, you will receive the updated array to.
NOTE: Because your array is always sorted, you can insert in correct position using binary search. This is very efficient.
I think the case comes down to careful management of postMessage calls and amount of data passed to be processed at a time. Was dealing with problem of this kind - think about not sending all new data into the function at once but rather creating your own queue and when small enough portion of the task has been acomplished by webworker thread send a message back to the main thread and decide to send the next portion, wait or quit.
In Your case, e.g. one time You get 9000 new items, next 100k - maybe create a queue/buffer that adds next 10k new elements each time webworker is done processing last data change.
const someWorker = new Worker('abc.js');
var processingLock = false;
var queue = [];
function newDataAction(arr = null) {
if (arr != null) {
queue = queue.concat(arr);
}
if (!processingLock) {
processingLock = true;
var data = [];
for (let i = 0; i < 10000 && queue.length > 0; i++) {
data.push(queue.pop());
}
worker.postMessage(data);
}
}
someWorker.addEventListener('message', function(e) {
if (e.data == 'finished-last-task') {
processingLock = false;
if (queue.length > 0) {
newDataAction();
}
}
});
Worked through many sorting algorithms and I don't see how sending new data into an sorting algorithm with partially sorted array makes much difference in terms of compuation time from sorting them both sequentially and performing a merge.
I have code as below.
I need to break the loop when first match is found.
const [isCodeValid, setIsCodeValid] = useState(false);
for (let i = 0; i < properyIds.length; i++) {
if (isCodeValid) {
break; // this breaks it but had to click twice so state would update
}
if (!isCodeValid) {
firestore().collection(`properties`)
.doc(`${properyIds[i]}`)
.collection('companies').get()
.then(companies => {
companies.forEach(company => {
if (_.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())) {
console.log("should break here")
// updating state like this wont take effect right away
// it shows true on second time click. so user need to click twice right now.
setIsCodeValid(true);
}
});
})
}
}
state won't update right away so if (!isCodeValid) only works on second click.
Once I find match I need to update state or variable so I can break the for loop.
I tried to use a variable but its value also not changing in final if condition, I wonder what is the reason? can anyone please explain ?
You should try and rewrite your code such that you will always call setIsCodeValid(value) once. In your case it could be called multiple times and it might not get called at all
const [isCodeValid, setIsCodeValid] = useState(false);
function checkForValidCode() {
// map to an array of promises for companies[]
const companiesPromises = properyIds.map(propertyId =>
firestore()
.collection(`properties`)
.doc(propertyId)
.collection('companies').get())
Promise.all(companiesPromises)
// flatten the 2d array to single array, re-create to JS array because of firestores internal types?
.then(companiesArray => [...companiesArray].flatMap(v => v))
// go through all companies to find a match
.then(companies =>
companies.find(
company => _.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())
))
.then(foundCompany => {
// code is valid if we found a matching company
setIsCodeValue(foundCompany !== undefined)
})
}
Try something like this:
import { useState } from 'react';
function YourComponent({ properyIds }) {
const [isCodeValid, setIsCodeValid] = useState(false);
async function handleSignupClick() {
if (isCodeValid) {
return;
}
for (let i = 0; i < properyIds.length; i++) {
const companies = await firestore()
.collection(`properties`)
.doc(`${properyIds[i]}`)
.collection('companies')
.get();
for (const company of companies.docs) {
if (_.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())) {
setIsCodeValid(true);
return;
}
}
}
}
return (<button onClick={handleSignupClick}>Sign Up</button>);
}
If you await these checks, that will allow you to sequentially loop and break out with a simple return, something you can't do inside of a callback. Note that if this is doing database queries, you should probably show waiting feedback while this is taking place so the user knows that clicking did something.
Update:
You may want to do all these checks in parallel if feasible so the user doesn't have to wait. Depends on your situation. Here's how you'd do that.
async function handleSignupClick() {
if (isCodeValid) {
return;
}
const allCompanies = await Promise.all(
properyIds.map(id => firestore()
.collection(`properties`)
.doc(`${properyIds[i]}`)
.collection('companies')
.get()
)
);
setIsCodeValid(
allCompanies.some(companiesSnapshot =>
companiesSnapshot.docs.some(company =>
_.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())
)
)
);
}
Can you not break it after setIsCodeValid(true);?
Use some:
companies.some(company => {
return _.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase());
});
If some and forEach are not available then companies is not an array but an array-like object. To iterate through those, we can use for of loop:
for (const company of companies){
if (_.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())) {
// do something
break;
}
}
I tired below and it worked for me to break the loop.
I declared and tried to change this variable let codeValid and it was just not updating its value when match found. (not sure why)
But all of a sudden I tried and it just works.
I didnt change any actual code except for variable.
let codeValid = false;
let userInformation = []
for (let i = 0; i < properties.length; i++) {
console.log("called")
const companies = await firestore().collection(`properties`)
.doc(`${properties[i].id}`)
.collection('companies').get()
.then(companies => {
companies.forEach(company => {
if (_.trim(company.data().registrationCode) === _.trim(registrationCode.toUpperCase())) {
// a += 1;
codeValid = true;
userInformation.registrationCode = registrationCode.toUpperCase();
userInformation.companyName = company.data().companyName;
userInformation.propertyName = properties[i].propertyName;
}
});
})
if (codeValid) {
break;
}
}
The following component's code is from an Angular 6 web application that I am creating. The app displays a table with CRUD functionality. I have an Angular service called GetDBValuesService that is connected to a database and uses DBValues() to retrieve an array of arrays (each inner array contains the values of a given row in the database). My code then collects rows whose 'Number' attribute is equal to 10. These rows are then used by my EventEmitter dataItems, which allows them to be displayed in my web page's CRUD table.
I have created another Angular service called DataService that receives an integer value from another component and sends that value to the shown component (after being subscribed to). I subscribed to this service in the following code and let an instance of gotdata (a public var declared in this component) receive the service's value. However, when I try to use this instance outside of that subscription (to replace the hardcoded 10 described above), this.gotdata is undefined.
How can I modify my code so that I can use the value given by the DataService service in the GetDBValuesService service? Currently, the below code does work due to the hardcoded 10, but does not if I remove that line. Thank you for taking the time to read this.
This is the portion of my CRUD component:
refresh = () => {
this.DataService.DataID$.subscribe((data) => {
this.gotdata = data;
console.log(this.gotdata); //10 (value from console)
});
console.log(this.gotdata); //undefined (value from console)
this.gotdata = 10; //hardcoded value allows further functionality, will be removed when this.gotdata retains its value from the above subscription
if (this.gotdata != null) {
this.GetDBValuesService.DBValues().subscribe((result) => {
var a = 0;
for (var i = 0; i < result.length; i++) {
if (result[i].Number == this.gotdata) {
this.info[a] = result[i];
a = a + 1;
}
}
this.dataItems.next(this.info); //sets rows to be displayed in the web page's table (used by component's HTML file)
});
}}
this.gotdata is undefined because the data is not resolved yet.
refresh = () => {
this.DataService.DataID$.subscribe((data) => {
this.gotdata = data;
console.log(this.gotdata); //10 (value from console)
if (this.gotdata != null) {
this.GetDBValuesService.DBValues().subscribe((result) => {
var a = 0;
for (var i = 0; i < result.length; i++) {
if (result[i].Number == this.gotdata) {
this.info[a] = result[i];
a = a + 1;
}
}
this.dataItems.next(this.info); //sets rows to be displayed in the web page's table (used by component's HTML file)
});
}}
});
Or you can put it inside subscription on complete callback:
this.service.subscribe((data) => {
// code here
},
(error) => console.error(error),
() => {
// do stuff.
});
The problem is that, at the time when you are calling the console.log(...) and the code below, data from the dataID$observable are still on way to you. ( Why do u need to work with observables?)
The best approach for this would to be use the RXJS switchMap operator (what is switchMap?). Because as I see you want to subscribe to the first observable and after that subscribe to another observable. So it can be done this way:
refresh = () => {
this.DataService.DataID$.pipe(switchMap(data: any) => {
if (data) {
this.gotdata = data;
return this.GetDBValuesService.DBValues();
} else {
return of(null); // if 'data' are null, return "empty" observable
}
})).subscribe((result: any) => {
if (!result) {
return; // return if 'result' is null (so the code bellow won't be executed)
}
var a = 0;
for (var i = 0; i < result.length; i++) {
if (result[i].Number == this.gotdata) {
this.info[a] = result[i];
a = a + 1;
}
}
this.dataItems.next(this.info);
});
Every minute I have a script that push a new record in my firebase database.
What i want is delete the last records when length of the list reach a fixed value.
I have been through the doc and other post and the thing I have found so far is something like that :
// Max number of lines of the chat history.
const MAX_ARDUINO = 10;
exports.arduinoResponseLength = functions.database.ref('/arduinoResponse/{res}').onWrite(event => {
const parentRef = event.data.ref.parent;
return parentRef.once('value').then(snapshot => {
if (snapshot.numChildren() >= MAX_ARDUINO) {
let childCount = 0;
let updates = {};
snapshot.forEach(function(child) {
if (++childCount <= snapshot.numChildren() - MAX_ARDUINO) {
updates[child.key] = null;
}
});
// Update the parent. This effectively removes the extra children.
return parentRef.update(updates);
}
});
});
The problem is : onWrite seems to download all the related data every time it is triggered.
This is a pretty good process when the list is not so long. But I have like 4000 records, and every month it seems that I screw up my firebase download quota with that.
Does anyone would know how to handle this kind of situation ?
Ok so at the end I came with 3 functions. One update the number of arduino records, one totally recount it if the counter is missing. The last one use the counter to make a query using the limitToFirst filter so it retrieve only the relevant data to remove.
It is actually a combination of those two example provided by Firebase :
https://github.com/firebase/functions-samples/tree/master/limit-children
https://github.com/firebase/functions-samples/tree/master/child-count
Here is my final result
const MAX_ARDUINO = 1500;
exports.deleteOldArduino = functions.database.ref('/arduinoResponse/{resId}/timestamp').onWrite(event => {
const collectionRef = event.data.ref.parent.parent;
const countRef = collectionRef.parent.child('arduinoResCount');
return countRef.once('value').then(snapCount => {
return collectionRef.limitToFirst(snapCount.val() - MAX_ARDUINO).transaction(snapshot => {
snapshot = null;
return snapshot;
})
});
});
exports.trackArduinoLength = functions.database.ref('/arduinoResponse/{resId}/timestamp').onWrite(event => {
const collectionRef = event.data.ref.parent.parent;
const countRef = collectionRef.parent.child('arduinoResCount');
// Return the promise from countRef.transaction() so our function
// waits for this async event to complete before it exits.
return countRef.transaction(current => {
if (event.data.exists() && !event.data.previous.exists()) {
return (current || 0) + 1;
} else if (!event.data.exists() && event.data.previous.exists()) {
return (current || 0) - 1;
}
}).then(() => {
console.log('Counter updated.');
});
});
exports.recountArduino = functions.database.ref('/arduinoResCount').onWrite(event => {
if (!event.data.exists()) {
const counterRef = event.data.ref;
const collectionRef = counterRef.parent.child('arduinoResponse');
// Return the promise from counterRef.set() so our function
// waits for this async event to complete before it exits.
return collectionRef.once('value')
.then(arduinoRes => counterRef.set(arduinoRes.numChildren()));
}
});
I have not tested it yet but soon I will post my result !
I also heard that one day Firebase will add a "size" query, that is definitely missing in my opinion.