In my extension I want to edit the document on a few specific document edits.
My actual use case is a bit complicated so I have created a minimal example. The code below listens for any document edit. If the word "hello" exists in the edit (i.e. the user pasted some code that contains the word "hello") then we replace the change range with the pasted text but just make it upper case.
We also console.log if the edit was successful, and any potential reason the edit was rejected.
vscode.workspace.onDidChangeTextDocument(event => {
for (const change of event.contentChanges) {
if (change.text.includes("hello")) {
activeEditor.edit(editBuilder => {
editBuilder.replace(change.range, change.text.toUpperCase());
}).then(
value => console.log("SUCCESS: "+value),
reason => console.log("FAIL REASON: "+reason),
);
}
}
});
A working example would be selecting some text in a document and pasting in the text const hello = 5;. As expected, the extension replaces the text with CONST HELLO = 5; and logs SUCCESS: true.
But when I paste in some text that automatically get formatted I run into problems. If I were to paste in:
const hello = 5;
const lol = 10;
const lmao = 20;
Including all the whitespaces/tabs, then vscode wants to "format" or correct my lines, i.e. remove the whitespace. So the resulting text will be:
const hello = 5;
const lol = 10;
const lmao = 20;
The extension tries to make it uppercase still but only prints SUCCESS: false. No reason is logged at all; the reject function is not executed.
Why does the edit not succeed? Should I await the other edits somehow or keep re-trying the edit until it succeeds? Am I logging the rejection incorrectly?
In case it helps, here is code I use - I found it better to have the editBuilder outside the loop. I think you can adapt it for your purposes:
editor.edit( (editBuilder) => {
// put your for (const change of event.contentChanges) {} here
for (const match of matches) {
resolvedReplace = variables.buildReplace(args, "replace", match, editor.selection, null, index);
const matchStartPos = document.positionAt(match.index);
const matchEndPos = document.positionAt(match.index + match[0].length);
const matchRange = new vscode.Range(matchStartPos, matchEndPos);
editBuilder.replace(matchRange, resolvedReplace);
}
}).then(success => {
if (!success) {
return;
}
if (success) { ... do something here if you need to }
});
One solution is just to "keep trying again". I do not like this solution, but it is a solution nevertheless, and it currently works for my use-case.
async function makeReplaceEdit(range: vscode.Range, text: string, maxRetries = 10) {
for (let i = 0; i <= maxRetries; i++) {
const editor = vscode.window.activeTextEditor;
if (!editor) return;
const success = await editor.edit(editBuilder => {
editBuilder.replace(
range,
text
);
}, { undoStopBefore: false, undoStopAfter: false });
if (success) break;
}
};
vscode.workspace.onDidChangeTextDocument((event) => {
// See if any change contained "hello"
let foundHello = false;
for (const change of event.contentChanges) {
if (change.text.includes("hello")) {
foundHello = true;
}
}
if (foundHello) {
console.log("inside1");
const editor = vscode.window.activeTextEditor;
if (!editor) return;
makeReplaceEdit(editor.document.lineAt(0).range, "Change");
}
});
I'm trying to replicate the code in this article:
https://depth-first.com/articles/2020/08/24/smiles-validation-in-the-browser/
What I'm trying to do different is that I'm using a textarea instead of input to take multi-line input. In addition to displaying an error message, I also want to display the entry which doesn't pass the validation.
The original validation script is this:
const path = '/target/wasm32-unknown-unknown/release/smival.wasm';
const read_smiles = instance => {
return smiles => {
const encoder = new TextEncoder();
const encoded = encoder.encode(`${smiles}\0`);
const length = encoded.length;
const pString = instance.exports.alloc(length);
const view = new Uint8Array(
instance.exports.memory.buffer, pString, length
);
view.set(encoded);
return instance.exports.read_smiles(pString);
};
};
const watch = instance => {
const read = read_smiles(instance);
document.querySelector('input').addEventListener('input', e => {
const { target } = e;
if (read(target.value) === 0) {
target.classList.remove('invalid');
} else {
target.classList.add('invalid');
}
});
}
(async () => {
const response = await fetch(path);
const bytes = await response.arrayBuffer();
const wasm = await WebAssembly.instantiate(bytes, { });
watch(wasm.instance);
})();
For working with a textarea, I've changed the watch function to this and added a <p id="indicator"> element to the html to display an error:
const watch = instance => {
const read = read_smiles(instance);
document.querySelector("textarea").addEventListener('input', e => {
const { target } = e;
var lines_array = target.value.split('/n');
var p = document.getElementById("indicator");
p.style.display = "block";
p.innerHTML = "The size of the input is : " + lines_array.length;
if (read(target.value) === 0) {
target.classList.remove('invalid');
} else {
target.classList.add('invalid');
}
});
}
I'm not even able to get a count of entries that fail the validation. I believe this is async js and I'm just a beginner in JavaScript so it's hard to follow what is happening here, especially the part where the function e is referencing itself.
document.querySelector("textarea").addEventListener('input', e => {
const { target } = e;
Can someone please help me in understanding this complicated code and figuring out how to get a count of entries that fail the validation and also printing the string/index of the same for helping the user?
There is a mistake in you code to count entries in the textarea:
var lines_array = target.value.split('\n'); // replace /n with \n
You are asking about the function e is referencing itself:
The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables. You can find more informations Mdn web docs - Destructuring object
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;
}
}
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.