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I am currently developing an app which interacts with uniswap, and I have developed a Wrapper class to contain the info and variables I'll need about some pair (e.g DAI/WETH).
As some of this values are asynchronous, I have coded a build() async function to get those before calling the constructor, so I can store them. I want to store the result of this build function, which is an instance of the class I have defined, inside a variable to use it later, but I need to know whether the Promise that that build function returns is resolved before using it, so how can I make it?
Here is the code of the class:
'use strict'
const { ChainId, Fetcher, WETH, Route, Trade, TokenAmoun, TradeType, TokenAmount } = require('#uniswap/sdk')
const { toChecksumAddress } = require('ethereum-checksum-address')
const Web3 = require('web3')
const web3 = new Web3()
const chainId = ChainId.MAINNET;
let tok1;
let tok2;
let pair;
let route;
let trade;
class UniswapTokenPriceFetcher
{
constructor(async_params)
{
async_params.forEach((element) => {
if (element === 'undefined')
{
throw new Error('All parameters must be defined')
}
});
this.trade = async_params[0];
this.route = async_params[1];
this.pair = async_params[2];
this.tok1 = async_params[3];
this.tok2 = async_params[4];
}
static async build(token1, token2)
{
var tok1 = await Fetcher.fetchTokenData(chainId, toChecksumAddress(token1))
var tok2 = await Fetcher.fetchTokenData(chainId, toChecksumAddress(token2))
var pair = await Fetcher.fetchPairData(tok1, tok2)
var route = new Route([pair], tok2)
var trade = new Trade(route, new TokenAmount(tok2, web3.utils.toWei('1', 'Ether')), TradeType.EXACT_INPUT)
return new UniswapTokenPriceFetcher([trade, route, pair, tok1, tok2])
}
getExecutionPrice6d = () =>
{
return this.trade.executionPrice.toSignificant(6);
}
getNextMidPrice6d = () =>
{
return this.trade.nextMidPrice.toSignificant(6);
}
}
module.exports = UniswapTokenPriceFetcher
Thank you everybody!
EDIT: I know Uniswap only pairs with WETH so one of my token variables is unneccesary, but the problem remains the same! Also keep in mind that I want to store an instance of this class for latter use inside another file.
You should either call the build function with await
const priceFetcher = await UniswapTokenPriceFetcher.build(token1, token2)
or followed by then
UniswapTokenPriceFetcher.build(token1, token2).then(priceFetcher => {...})
I don't see any other way.
I need some advice on how to structure this function as at the moment it is not happening in the correct order due to node being asynchronous.
This is the flow I want to achieve; I don't need help with the code itself but with the order to achieve the end results and any suggestions on how to make it efficient
Node routes a GET request to my controller.
Controller reads a .csv file on local system and opens a read stream using fs module
Then use csv-parse module to convert that to an array line by line (many 100,000's of lines)
Start a try/catch block
With the current row from the csv, take a value and try to find it in a MongoDB
If found, take the ID and store the line from the CSV and this id as a foreign ID in a separate database
If not found, create an entry into the DB and take the new ID and then do 6.
Print out to terminal the row number being worked on (ideally at some point I would like to be able to send this value to the page and have it update like a progress bar as the rows are completed)
Here is a small part of the code structure that I am currently using;
const fs = require('fs');
const parse = require('csv-parse');
function addDataOne(req, id) {
const modelOneInstance = new InstanceOne({ ...code });
const resultOne = modelOneInstance.save();
return resultOne;
}
function addDataTwo(req, id) {
const modelTwoInstance = new InstanceTwo({ ...code });
const resultTwo = modelTwoInstance.save();
return resultTwo;
}
exports.add_data = (req, res) => {
const fileSys = 'public/data/';
const parsedData = [];
let i = 0;
fs.createReadStream(`${fileSys}${req.query.file}`)
.pipe(parse({}))
.on('data', (dataRow) => {
let RowObj = {
one: dataRow[0],
two: dataRow[1],
three: dataRow[2],
etc,
etc
};
try {
ModelOne.find(
{ propertyone: RowObj.one, propertytwo: RowObj.two },
'_id, foreign_id'
).exec((err, searchProp) => {
if (err) {
console.log(err);
} else {
if (searchProp.length > 1) {
console.log('too many returned from find function');
}
if (searchProp.length === 1) {
addDataOne(RowObj, searchProp[0]).then((result) => {
searchProp[0].foreign_id.push(result._id);
searchProp[0].save();
});
}
if (searchProp.length === 0) {
let resultAddProp = null;
addDataTwo(RowObj).then((result) => {
resultAddProp = result;
addDataOne(req, resultAddProp._id).then((result) => {
resultAddProp.foreign_id.push(result._id);
resultAddProp.save();
});
});
}
}
});
} catch (error) {
console.log(error);
}
i++;
let iString = i.toString();
process.stdout.clearLine();
process.stdout.cursorTo(0);
process.stdout.write(iString);
})
.on('end', () => {
res.send('added');
});
};
I have tried to make the functions use async/await but it seems to conflict with the fs.openReadStream or csv parse functionality, probably due to my inexperience and lack of correct use of code...
I appreciate that this is a long question about the fundamentals of the code but just some tips/advice/pointers on how to get this going would be appreciated. I had it working when the data was sent one at a time via a post request from postman but can't implement the next stage which is to read from the csv file which contains many records
First of all you can make the following checks into one query:
if (searchProp.length === 1) {
if (searchProp.length === 0) {
Use upsert option in mongodb findOneAndUpdate query to update or upsert.
Secondly don't do this in main thread. Use a queue mechanism it will be much more efficient.
Queue which I personally use is Bull Queue.
https://github.com/OptimalBits/bull#basic-usage
This also provides the functionality you need of showing progress.
Also regarding using Async Await with ReadStream, a lot of example can be found on net such as : https://humanwhocodes.com/snippets/2019/05/nodejs-read-stream-promise/
My goals are to obtain the users nickname by using their ID.
Their ID's are stored as variables which are being collected from a reaction collector.
I have tried a few methods and failed, most of which either return nothing or errors.
The below code returns nothing, the getnames() function is empty. This method was recommended to me buy 2 people from a nodejs discord server which aims to help solve issues, similar to here.
// returns player ID's
function getPlayers() {
let players = [];
players.push(queue.tank[0]); // First (1) in TANK queue
players.push(queue.heal[0]); // First (1) in HEAL queue
players.push(queue.dps[0]); // First (2) in DPS queue
players.push(queue.dps[1]);
return players;
}
// get nick names from ID's
function getnames() {
let players = getPlayers();
let playerNicks = [];
let newPlayer = "";
players.forEach(async player => {
newPlayer = await message.guild.members.fetch(player).then(function (user) {return user.displayName });
playerNicks.push(newPlayer)
return playerNicks;
})}
//formats nicknames into string
function formatnicknames() {
let formatted_string2 = '';
let playerNicks = getnames();
if (playerNicks)
formatted_string2 = `${playerNicks[0]} \n${playerNicks[1]} \n${playerNicks[2]} \n${playerNicks[3]}`;
return formatted_string2;
}
I have also tried a few variations of the below code, still unable to obtain nickname.
message.guild.members.cache.get(user.id)
Edit #1
now tried the following code with no success. (boost1ID contains the ID of 1 user)
var mem1 = message.guild.members.fetch(boost1ID).nickname
Edit #2
tried a new method of obtaining displayname from ID.
var guild = client.guilds.cache.get('guildid');
var mem1 = guild.member(boost1ID);
var mem2 = guild.member(boost2ID);
var mem3 = guild.member(boost3ID);
var mem4 = guild.member(boost4ID);
var nickname1 = mem1 ? mem1.displayName : null;
var nickname2 = mem2 ? mem2.displayName : null;
var nickname3 = mem3 ? mem3.displayName : null;
var nickname4 = mem4 ? mem4.displayName : null;
var Allnicknames = `${nickname1} ${nickname2} ${nickname3} ${nickname4}`
message.channel.send(`testing nicknames: ${Allnicknames}`)
I managed to only return my own name since i dont have a nickname on this server, but the other three users who does have a nickname returned null.
This is the simplest solution:
// your users ids
const IDs = [ '84847448498748974', '48477847847844' ];
const promises = IDs.map((userID) => {
return new Promise(async (resolve) => {
const member = message.guild.member(userID) || await message.guild.members.fetch(userID);
resolve(member.displayName || member.user.username);
});
});
const nicknames = await Promise.all(promises);
// you now have access to ALL the nicknames, even if the members were not cached!
The members you are trying to get the nicknames of are not necessarily cached, and this fixes that.
I made an example that could help you.
let testUsers = [];
module.exports = class extends Command {
constructor(...args) {
super(...args, {
description: 'Testing.',
category: "Information",
});
}
async run(message) {
function getNicknames(userArr, guild) {
let playerNicks = [];
for(var i = 0; i < userArr.length; i++) {
playerNicks.push(guild.member(userArr[i]).displayName);
}
return playerNicks;
}
let testUser = message.guild.members.cache.get(message.author.id);
testUsers.push(testUser);
let guild = message.guild;
console.log(getNicknames(testUsers, guild));
}
}
I created a function getNicknames that takes in two parameters. The first one is an Array of users (as you get one from your function getPlayers()) and the second one is the guild you are playing in. You need to provide the guild, because every user should be a GuildMember, because you want to use .displayName. I created a user Array outside of my command code, because otherwise there will only be one user in the Array everytime you use the command. Inside of the getNicknames() function I have created a new Array playerNicks that I basically fill with the user nicknames we get from our provided user Array.
Now you have to implement that into your code.
The call of the function getNicknames(), for your code should look like this:
getNicknames(getPlayers(), message.guild);
I'm using an Observable to provide event subscription interface for clients from a global resource, and I need to manage that resource according to the number of active subscriptions:
Allocate global resource when the number of subscriptions becomes greater than 0
Release global resource when the number of subscriptions becomes 0
Adjust the resource usage strategy based on the number of subscriptions
What is the proper way in RXJS to monitor the number of active subscriptions?
How to implement the following within RXJS syntax? -
const myEvent: Observable<any> = new Observable();
myEvent.onSubscription((newCount: number, prevCount: number) => {
if(newCount === 0) {
// release global resource
} else {
// allocate global resource, if not yet allocated
}
// for a scalable resource usage / load,
// re-configure it, based on newCount
});
I wouldn't expect a guaranteed notification on each change, hence newCount + prevCount params.
UPDATE-1
This is not a duplicate to this, because I need to be notified when the number of subscriptions changes, and not just to get the counter at some point.
UPDATE-2
Without any answer so far, I quickly came up with a very ugly and limited work-around, through complete incapsulation, and specifically for type Subject. Hoping very much to find a proper solution.
UPDATE-3
After a few answers, I'm still not sure how to implement what I'm trying, which is the following:
class CustomType {
}
class CountedObservable<T> extends Observable<T> {
private message: string; // random property
public onCount; // magical Observable that needs to be implemented
constructor(message: string) {
// super(); ???
this.message = message;
}
// random method
public getMessage() {
return this.message;
}
}
const a = new CountedObservable<CustomType>('hello'); // can create directly
const msg = a.getMessage(); // can call methods
a.subscribe((data: CustomType) => {
// handle subscriptions here;
});
// need that magic onCount implemented, so I can do this:
a.onCount.subscribe((newCount: number, prevCont: number) => {
// manage some external resources
});
How to implement such class CountedObservable above, which would let me subscribe to itself, as well as its onCount property to monitor the number of its clients/subscriptions?
UPDATE-4
All suggested solutions seemed overly complex, and even though I accepted one of the answers, I ended up with a completely custom solution one of my own.
You could achieve it using defer to track subscriptions and finalize to track completions, e.g. as an operator:
// a custom operator that will count number of subscribers
function customOperator(onCountUpdate = noop) {
return function refCountOperatorFunction(source$) {
let counter = 0;
return defer(()=>{
counter++;
onCountUpdate(counter);
return source$;
})
.pipe(
finalize(()=>{
counter--;
onCountUpdate(counter);
})
);
};
}
// just a stub for `onCountUpdate`
function noop(){}
And then use it like:
const source$ = new Subject();
const result$ = source$.pipe(
customOperator( n => console.log('Count updated: ', n) )
);
Heres a code snippet illustrating this:
const { Subject, of, timer, pipe, defer } = rxjs;
const { finalize, takeUntil } = rxjs.operators;
const source$ = new Subject();
const result$ = source$.pipe(
customOperator( n => console.log('Count updated: ', n) )
);
// emit events
setTimeout(()=>{
source$.next('one');
}, 250);
setTimeout(()=>{
source$.next('two');
}, 1000);
setTimeout(()=>{
source$.next('three');
}, 1250);
setTimeout(()=>{
source$.next('four');
}, 1750);
// subscribe and unsubscribe
const subscriptionA = result$
.subscribe(value => console.log('A', value));
setTimeout(()=>{
result$.subscribe(value => console.log('B', value));
}, 500);
setTimeout(()=>{
result$.subscribe(value => console.log('C', value));
}, 1000);
setTimeout(()=>{
subscriptionA.unsubscribe();
}, 1500);
// complete source
setTimeout(()=>{
source$.complete();
}, 2000);
function customOperator(onCountUpdate = noop) {
return function refCountOperatorFunction(source$) {
let counter = 0;
return defer(()=>{
counter++;
onCountUpdate(counter);
return source$;
})
.pipe(
finalize(()=>{
counter--;
onCountUpdate(counter);
})
);
};
}
function noop(){}
<script src="https://unpkg.com/rxjs#6.4.0/bundles/rxjs.umd.min.js"></script>
* NOTE: if your source$ is cold — you might need to share it.
Hope it helps
You are really asking three separate questions here, and I question whether you really need the full capability that you mention. Since most of the resource managment stuff you are asking for is already provided for by the library, doing custom tracking code seems to be redundant. The first two questions:
Allocate global resource when the number of subscriptions becomes greater than 0
Release global resource when the number of subscriptions becomes 0
Can be done with the using + share operators:
class ExpensiveResource {
constructor () {
// Do construction
}
unsubscribe () {
// Do Tear down
}
}
// Creates a resource and ties its lifecycle with that of the created `Observable`
// generated by the second factory function
// Using will accept anything that is "Subscription-like" meaning it has a unsubscribe function.
const sharedStream$ = using(
// Creates an expensive resource
() => new ExpensiveResource(),
// Passes that expensive resource to an Observable factory function
er => timer(1000)
)
// Share the underlying source so that global creation and deletion are only
// processed when the subscriber count changes between 0 and 1 (or visa versa)
.pipe(share())
After that sharedStream$ can be passed around as a base stream which will manage the underlying resource (assuming you implemented your unsubscribe correctly) so that the resource will be created and torn down as the number of subscribers transitions between 0 and 1.
Adjust the resource usage strategy based on the number of subscriptions
The third question I am most dubious on, but I'll answer it for completeness assuming you know your application better than I do (since I can't think of a reason why you would need specific handling at different usage levels other than going between 0 and 1).
Basically I would use a similar approach as above but I would encapuslate the transition logic slightly differently.
// Same as above
class ExpensiveResource {
unsubscribe() { console.log('Tear down this resource!')}
}
const usingReferenceTracking =
(onUp, onDown) => (resourceFactory, streamFactory) => {
let instance, refCount = 0
// Again manage the global resource state with using
const r$ = using(
// Unfortunately the using pattern doesn't let the resource escape the closure
// so we need to cache it for ourselves to use later
() => instance || (instance = resourceFactory()),
// Forward stream creation as normal
streamFactory
)
).pipe(
// Don't forget to clean up the stream after all is said and done
// Because its behind a share this should only happen when all subscribers unsubscribe
finalize(() => instance = null)
share()
)
// Use defer to trigger "onSubscribe" side-effects
// Note as well that these side-effects could be merged with the above for improved performance
// But I prefer them separate for easier maintenance.
return defer(() => onUp(instance, refCount += 1) || r$)
// Use finalize to handle the "onFinish" side-effects
.pipe(finalize(() => onDown(instance, refCount -= 1)))
}
const referenceTracked$ = usingReferenceTracking(
(ref, count) => console.log('Ref count increased to ' + count),
(ref, count) => console.log('Ref count decreased to ' + count)
)(
() => new ExpensiveResource(),
ref => timer(1000)
)
referenceTracked$.take(1).subscribe(x => console.log('Sub1 ' +x))
referenceTracked$.take(1).subscribe(x => console.log('Sub2 ' +x))
// Ref count increased to 1
// Ref count increased to 2
// Sub1 0
// Ref count decreased to 1
// Sub2 0
// Ref count decreased to 0
// Tear down this resource!
Warning: One side effect of this is that by definition the stream will be warm once it leaves the usingReferenceTracking function, and it will go hot on first subscription. Make sure you take this into account during the subscription phase.
What a fun problem! If I am understanding what you are asking, here is my solution to this: create a wrapper class around Observable that tracks the subscriptions by intercepting both subscribe() and unsubscribe(). Here is the wrapper class:
export class CountSubsObservable<T> extends Observable<T>{
private _subCount = 0;
private _subCount$: BehaviorSubject<number> = new BehaviorSubject(0);
public subCount$ = this._subCount$.asObservable();
constructor(public source: Observable<T>) {
super();
}
subscribe(
observerOrNext?: PartialObserver<T> | ((value: T) => void),
error?: (error: any) => void,
complete?: () => void
): Subscription {
this._subCount++;
this._subCount$.next(this._subCount);
let subscription = super.subscribe(observerOrNext as any, error, complete);
const newUnsub: () => void = () => {
if (this._subCount > 0) {
this._subCount--;
this._subCount$.next(this._subCount);
subscription.unsubscribe();
}
}
subscription.unsubscribe = newUnsub;
return subscription;
}
}
This wrapper creates a secondary observable .subCount$ that can be subscribed to which will emit every time the number of subscriptions to the source observable changes. It will emit a number corresponding to the current number of subscribers.
To use it you would create a source observable and then call new with this class to create the wrapper. For example:
const source$ = interval(1000).pipe(take(10));
const myEvent$: CountSubsObservable<number> = new CountSubsObservable(source$);
myEvent$.subCount$.subscribe(numSubs => {
console.log('subCount$ notification! Number of subscriptions is now', numSubs);
if(numSubs === 0) {
// release global resource
} else {
// allocate global resource, if not yet allocated
}
// for a scalable resource usage / load,
// re-configure it, based on numSubs
});
source$.subscribe(result => console.log('result is ', result));
To see it in use, check out this Stackblitz.
UPDATE:
Ok, as mentioned in the comments, I'm struggling a little to understand where the stream of data is coming from. Looking back through your question, I see you are providing an "event subscription interface". If the stream of data is a stream of CustomType as you detail in your third update above, then you may want to use fromEvent() from rxjs to create the source observable with which you would call the wrapper class I provided.
To show this I created a new Stackblitz. From that Stackblitz here is the stream of CustomTypes and how I would use the CountedObservable class to achieve what you are looking for.
class CustomType {
a: string;
}
const dataArray = [
{ a: 'January' },
{ a: 'February' },
{ a: 'March' },
{ a: 'April' },
{ a: 'May' },
{ a: 'June' },
{ a: 'July' },
{ a: 'August' },
{ a: 'September' },
{ a: 'October' },
{ a: 'November' },
{ a: 'December' }
] as CustomType[];
// Set up an arbitrary source that sends a stream of `CustomTypes`, one
// every two seconds by using `interval` and mapping the numbers into
// the associated dataArray.
const source$ = interval(2000).pipe(
map(i => dataArray[i]), // transform the Observable stream into CustomTypes
take(dataArray.length), // limit the Observable to only emit # array elements
share() // turn into a hot Observable.
);
const myEvent$: CountedObservable<CustomType> = new CountedObservable(source$);
myEvent$.onCount.subscribe(newCount => {
console.log('newCount notification! Number of subscriptions is now', newCount);
});
I hope this helps.
First of all, I very much appreciate how much time and effort people have committed trying to answer my question! And I am sure those answers will prove to be a useful guideline to other developers, solving similar scenarios with RXJS.
However, specifically for what I was trying to get out of RXJS, I found in the end that I am better off not using it at all. I specifically wanted the following:
A generic, easy-to-use interface for subscribing to notifications, plus monitoring subscriptions - all in one. With RXJS, the best I would end up is some workarounds that appear to be needlessly convoluted or even cryptic to developers who are not experts in RXJS. That is not what I would consider a friendly interface, more like something that rings over-engineering.
I ended up with a custom, much simpler interface that can do everything I was looking for:
export class Subscription {
private unsub: () => void;
constructor(unsub: () => void) {
this.unsub = unsub;
}
public unsubscribe(): void {
if (this.unsub) {
this.unsub();
this.unsub = null; // to prevent repeated calls
}
}
}
export class Observable<T = any> {
protected subs: ((data: T) => void)[] = [];
public subscribe(cb: (data: T) => void): Subscription {
this.subs.push(cb);
return new Subscription(this.createUnsub(cb));
}
public next(data: T): void {
// we iterate through a safe clone, in case an un-subscribe occurs;
// and since Node.js is the target, we are using process.nextTick:
[...this.subs].forEach(cb => process.nextTick(() => cb(data)));
}
protected createUnsub(cb) {
return () => {
this.subs.splice(this.subs.indexOf(cb), 1);
};
}
}
export interface ISubCounts {
newCount: number;
prevCount: number;
}
export class CountedObservable<T = any> extends Observable<T> {
readonly onCount: Observable<ISubCounts> = new Observable();
protected createUnsub(cb) {
const s = this.subs;
this.onCount.next({newCount: s.length, prevCount: s.length - 1});
return () => {
s.splice(s.indexOf(cb), 1);
this.onCount.next({newCount: s.length, prevCount: s.length + 1});
};
}
}
It is both small and elegant, and lets me do everything I needed to begin with, in a safe and friendly manner. I can do the same subscribe and onCount.subscribe, and get all the same notifications:
const a = new CountedObservable<string>();
const countSub = a.onCount.subscribe(({newCount, prevCount}) => {
console.log('COUNTS:', newCount, prevCount);
});
const sub1 = a.subscribe(data => {
console.log('SUB-1:', data);
});
const sub2 = a.subscribe(data => {
console.log('SUB-2:', data);
});
a.next('hello');
sub1.unsubscribe();
sub2.unsubscribe();
countSub.unsubscribe();
I hope this will help somebody else also.
P.S. I further improved it as an independent module.
I have Redis with a lot of keys in some format and I want to get keys that match some pattern and do some operations on them. I don't use KEYS method since it's not recommend in production. Using SCAN I'm wondering what is the best way to write it in code. I have to do something like a while loop but using promises, my current solution looks like this (code is simplified a little):
'use strict'
const Promise = require('bluebird');
const config = require('./config');
const client = require('./clinet');
let iterator = 0;
Promise.coroutine(function* () {
do {
iterator = yield clinet.scanAsync(iterator, 'myQuery', 'COUNT', config.scanChunkSize)
.then(data => {
let nextIterator = data[0];
let values = data[1];
//do some magic with values
return nextIterator;
})
} while (iterator !== '0');
})();
Is there a better way to do it that I'm missing?
I realize this is a really old question, but I found all of the other answers very unsatisfying. Here is yet another attempt to scan in a relatively clean way using async await (WITHOUT the use of yet another external dependency). You can easily modify this to continuously delete each set of found keys (you would want to tackle them in batches like this in case there are LOTS). Pushing them into an array just demonstrates one very basic thing you could do with them during this stage.
const redis = require('redis');
const { promisify } = require('util');
const client = redis.createClient({...opts});
const scan = promisify(client.scan).bind(client);
const scanAll = async (pattern) => {
const found = [];
let cursor = '0';
do {
const reply = await scan(cursor, 'MATCH', pattern);
cursor = reply[0];
found.push(...reply[1]);
} while (cursor !== '0');
return found;
}
You can use recursion to keep calling scan until done.
function scanAsync(cursor, pattern, returnSet){
return redisClient.scanAsync(cursor, "MATCH", pattern, "COUNT", "100").then(
function (reply) {
cursor = reply[0];
var keys = reply[1];
keys.forEach(function(key,i){
returnSet.add(key);
});
if( cursor === '0' ){
return Array.from(returnSet);
}else{
return scanAsync(cursor, pattern, returnSet)
}
});
}
Pass in a Set() to make sure keys aren't duplicated
myResults = new Set();
scanAsync('0', "NOC-*[^listen]*", myResults).map(
function( myResults ){ console.log( myResults); }
);
You can try this snippet to scan (1000) keys per iteration and 'delete`.
var cursor = '0';
function scan(pattern,callback){
redisClient.scan(cursor, 'MATCH',pattern,'COUNT', '1000', function(err, reply){
if(err){
throw err;
}
cursor = reply[0];
if(cursor === '0'){
return callback();
}else{
var keys = reply[1];
keys.forEach(function(key,i){
redisClient.del(key, function(deleteErr, deleteSuccess){
console.log(key);
});
});
return scan(pattern,callback);
}
});
}
scan(strkey,function(){
console.log('Scan Complete');
});
Nice option for node-redis module is to use scan iterators. Example:
const redis = require("redis");
const client = redis.createClient();
async function getKeys(pattern="*", count=10) {
const results = [];
const iteratorParams = {
MATCH: pattern,
COUNT: count
}
for await (const key of client.scanIterator(iteratorParams)) {
results.push(key);
}
return results;
}
(Of course you can also process your keys on the fly in for await loop without storing them in additional array if that's enough for you).
If you do not want to override scan parameters (MATCH/COUNT) you can just skip them and execute client.scanIterator() without parameter (defaults will be used then, MATCH="*", COUNT=10).
I think the node bindings for Redis are pushing too much responsibility to the caller here. So I created my own library for scanning as well, using generators in node:
const redis = require('redis')
const client = redis.createClient(…)
const generators = require('redis-async-gen')
const { keysMatching } = generators.using(client)
…
for await (const key of keysMatching('test*')) {
console.info(key)
}
It's the last bit that obviously is the thing that you should care about. Instead of having to carefully control an iterator yourself, all you need to do is use a for comprehension.
I wrote more about it here.
Go through this, it may help.
https://github.com/fritzy/node-redisscan
do not use the library as it, go through the code available at
https://github.com/fritzy/node-redisscan/blob/master/index.js