I want to make this read calls async. It should output to the console 'finish' and then 'done'.
But the script wait first to finish the loop. Why it's not working?
const db = require('quick.db');
var balance = null;
var items = null;
final();
console.log('finish');
async function final() {
var res = await test();
console.log('done');
}
async function test() {
return new Promise((resolve, reject) => {
for(var i=0; i<10000; i++) {
balance = db.get('userInfo.balance') // -> 1000
items = db.get('userInfo.items') // ['Sword', 'Watch']
}
resolve(true);
});
}
So I have just copied and pasted your code and it works just the way you described it. It prints 'finish' and then 'done'. I'm not sure what's your question. However, I have a question about your code: Why would you use async and implicitly return a new Promise?
In addition to the above, you're trying to read some values from the db and they have not been set previously. I edited a bit your code:
const db = require('quick.db');
var balance = null;
var items = null;
db.set('userInfo', { difficulty: 'Easy' });
db.add('userInfo.balance', 1000);
db.push('userInfo.items', 'Sword');
db.push('userInfo.items', 'Watch');
final();
console.log('finish');
async function final() {
var res = await test();
console.log(`Balance: ${balance} | Items: ${items}`);
console.log('done');
}
async function test() {
for (var i = 0; i < 10000; i++) {
balance = db.get('userInfo.balance'); // -> 1000
items = db.get('userInfo.items'); // ['Sword', 'Watch']
}
}
Does it address your question?
Related
I have a use case where I need to perform a batch_write operation on dynamodb. I referred this article which has a good solution for similar use case. I implemented it with few cleanup in my code and it works as expected.
const _ = require('lodash');
// helper methods
async function asyncForEach(array, cb) {
await Promise.all(array.map(async (item) => {
await cb(item, array);
}));
}
function to(promise) {
return promise.then((data) => [null, data])
.catch((err) => [err]);
}
const call = function (params) {
return dynamoDb.batchWriteItem(params).promise();
};
async function batchWrite25(arrayOf25, tableName) {
// 25 is as many as you can write in one time
const itemsArray = [];
_.forEach(arrayOf25, (item) => {
itemsArray.push({
PutRequest: {
Item: item,
},
});
});
const params = {
RequestItems: {
[tableName]: itemsArray,
},
};
await to(call(params));
}
async function batchWrite(itemArray, tableName) {
let mainIndex = 0;
let subIndex = 0;
let arrayOf25 = [];
const arrayLength = itemArray.length;
await asyncForEach(itemArray, async (item) => {
arrayOf25.push(item);
subIndex += 1;
mainIndex += 1;
// 25 is as many as you can write in one time
if (subIndex % 25 === 0 || mainIndex === arrayLength) {
await to(batchWrite25(arrayOf25, tableName));
subIndex = 0; // reset
arrayOf25 = [];
}
});
}
module.exports = {
batchWrite,
};
However, the code looks a bit complicated here with so many callbacks involved. Is there a cleaner way of writing the same thing without using -- call or asyncForEach or to methods ?
Here's one simple way to batch the items:
const BATCH_MAX = 25;
const batchWrite = async (items, table_name) => {
const BATCHES = Math.floor((items.length + BATCH_MAX - 1) / BATCH_MAX);
for (let batch = 0; batch < BATCHES; batch++) {
const itemsArray = [];
for (let ii = 0; ii < BATCH_MAX; ii++) {
const index = batch * BATCH_MAX + ii;
if (index >= items.length) break;
itemsArray.push({
PutRequest: {
Item: items[index],
},
});
}
const params = {
RequestItems: {
[table_name]: itemsArray,
},
};
console.log("Batch", batch, "write", itemsArray.length, "items");
await dynamodb.batchWriteItem(params).promise();
}
};
To make the entire process asynchronous, you can convert this function to return an array of promises and later call Promise.all(promises) on that array. For example:
const batchWrite = (items, table_name) => {
const promises = [];
const BATCHES = Math.floor((items.length + BATCH_MAX - 1) / BATCH_MAX);
for (let batch = 0; batch < BATCHES; batch++) {
// same code as above here ...
promises.push(dynamodb.batchWriteItem(params).promise());
}
return promises;
};
A much cleaner way using lodash that worked for me is listed below. Hope this helps somone.
batchWrite=async ()=> {
const batchSplitArr=_.chunk(this.dynamoPayload,25); //dynamoPayload has the entire payload in the desired format for dynamodb insertion.
await Promise.all(
batchSplitArr.map(async (item) => {
const params = {
RequestItems: {
[this.tableName]: item,
},
};
await this.dynamoDb.batchWriteItem(params).promise();
})
);
};
please someone help, I just cant get it.
Can you please help on how to make async/await or promise (doneCb), so script waits for first vlc_snmp(..) to finish and then to call next?
Example:
function doneCb(error) {
console.log(final_result);
final_result = [];
if (error)
console.error(error.toString());
}
function feedCb(varbinds) {
for (var i = 0; i < varbinds.length; i++) {
if (snmp.isVarbindError(varbinds[i]))
console.error(snmp.varbindError(varbinds[i]));
else {
var snmp_rez = {
oid: (varbinds[i].oid).toString()
value: (varbinds[i].value).toString()
};
final_result.push(snmp_rez);
}
}
}
var session = snmp.createSession(VLC_IP, "public", options);
var maxRepetitions = 20;
function vlc_snmp(OID) {
session.subtree(OID_, maxRepetitions, feedCb, doneCb);
}
vlc_snmp(OID_SERIAL_NUMBER);
//wait OID_SERIAL_NUMBER to finish and then call next
vlc_snmp(OID_DEVICE_NAME);
You should be able to use the async / await statements to wait for your done callback to be called. We wrap this callback in the vlc_snmp function, and return a Promise. This allows us to use the await statement.
I've mocked out some of the code that I don't have access to, it should behave somewhat similarly to the real code.
The key point here is, when a function returns a Promise we can await the result in an async function, that will give you the behaviour you wish.
final_result = [];
const VLC_IP = "";
const options = {};
const OID_ = "OID_";
const OID_SERIAL_NUMBER = "OID_SERIAL_NUMBER"
const OID_DEVICE_NAME = "OID_DEVICE_NAME"
// Mock out snmp to call feedcb and donecb
const snmp = {
createSession(...args) {
return {
subtree(oid, maxRepetitions, feedCb, doneCb) {
setTimeout(feedCb, 500, [{ oid, value: 42}])
setTimeout(doneCb, 1000);
}
}
},
isVarbindError(input) {
return false;
}
}
function doneCb(error) {
console.log("doneCb: final_result:", final_result);
final_result = [];
if (error)
console.error("doneCb: Error:", error.toString());
}
function feedCb(varbinds) {
for (var i = 0; i < varbinds.length; i++) {
if (snmp.isVarbindError(varbinds[i]))
console.error(snmp.varbindError(varbinds[i]));
else {
var snmp_rez = {
oid: (varbinds[i].oid).toString(),
value: (varbinds[i].value).toString()
};
final_result.push(snmp_rez);
}
}
}
var session = snmp.createSession(VLC_IP, "public", options);
var maxRepetitions = 20;
function vlc_snmp(OID) {
return new Promise((resolve,reject) => {
session.subtree(OID, maxRepetitions, feedCb, (error) => {
// This is a wrapper callback on doneCb
// Always call the doneCb
doneCb(error);
if (error) {
reject(error);
} else {
resolve();
}
});
});
}
async function run_vls_snmp() {
console.log("run_vls_snmp: Calling vlc_snmp(OID_SERIAL_NUMBER)...");
await vlc_snmp(OID_SERIAL_NUMBER);
console.log("run_vls_snmp: Calling vlc_snmp(OID_DEVICE_NAME)...");
//wait OID_SERIAL_NUMBER to finish and then call next
await vlc_snmp(OID_DEVICE_NAME);
}
run_vls_snmp();
I want to save each array data into each document at Nodejs.
Therefore I made this code below.
But when I run this code, it only saves body[0].
Could you recommend some solution?
exports.saveOrder = (req, res) => {
const body = JSON.parse(res);
for (let i = 0; i < body.length; i += 1) {
const eachBody = body[i];
const order = new Order(eachBody);
order.save();
return res.send('order is saved');
}
}
}
};
For Db operations, You need to use promise or async/await, and send response once after all orders saved to DB. Add try/catch to catch errors as well.
Check this code, it should work now.
exports.saveOrder = async (req, res) => {
try {
const body = JSON.parse(res); // check this before do you realy need to parse it or not
const allResults = [];
for (let i = 0; i < body.length; i += 1) {
const eachBody = body[i];
const order = new Order(eachBody);
const result = await order.save();
allResults.push(result);
}
return res.send(allResults);
} catch (e) {
console.log(e);
return res.send(e);
}
};
This is because you have send the response(used return) inside the for loop.
So it saves body[0] and return the response.
Use "return" outside the "for loop".
for (let i = 0; i < body.length; i += 1) {
const eachBody = body[i];
const order = new Order(eachBody);
order.save();
}
return res.send('order is saved');
I currently have two promises, whereas the child is dependent on the parents success. I want to Resolve/reject the parent promise from the child promises "then".
const UserApplicaiton = require('../applications/user'), User = new UserApplicaiton();
class CheckParams {
constructor() { }
required(params, required_params) {
return new Promise(function(resolve, reject, onCancel) {
// set i
var i;
// set missed_required_params
var missed_required_params = [];
// check for userCredentials if user_id is required param, convert from credentials to user_id
if(required_params.includes("user_id")){
// set as const
const user_key = String(params.userCredentials.user_key);
const user_secret = String(params.userCredentials.user_secret);
// check in database
User.info(user_key, user_secret).then((data) => {
// if data
if(data) {
// add user_id to params
params.user_id = data[0]._id;
// loop params
for(i = 0; i < required_params.length; i++){
// if params that's required is there, else add to array
if(!(required_params[i] in params)){
missed_required_params.push(required_params[i]);
}
}
if(missed_required_params.length !== 0){
reject("Missed parameters: " + missed_required_params);
}else{
resolve(params);
}
}
}).catch((err) => {
reject(err);
});
}else{
// loop params
for(i = 0; i < required_params.length; i++){
// if params that's required is there, else add to array
if(!(required_params[i] in params)){
missed_required_params.push(required_params[i]);
}
}
if(missed_required_params.length !== 0){
console.log("hello");
return reject("Missed parameters: " + missed_required_params);
}else{
console.log("hello2");
resolve(1);
}
}
});
}
}
module.exports = CheckParams;
The goal for the second promise is to add to an object based on the response, and then resolve the parent promise, which will be used later in the code.
This doesn't work at all. Async doesn't really help.
Your problem appears to be that if(data) { is missing an else clause where you would settle the promise as well. Avoiding the Promise constructor antipattern helps to avoid such mistakes as well.
required(params, required_params) {
var promise;
if (required_params.includes("user_id")) {
const user_key = String(params.userCredentials.user_key);
const user_secret = String(params.userCredentials.user_secret);
promise = User.info(user_key, user_secret).then((data) => {
if (data) {
params.user_id = data[0]._id;
}
// else
// throw error? keep user_id undefined?
})
} else {
promise = Promise.resolve();
}
return promise.then(() => {
var missed_required_params = [];
for (var i = 0; i < required_params.length; i++) {
if (!(required_params[i] in params)) {
missed_required_params.push(required_params[i]);
}
}
if (missed_required_params.length !== 0) {
throw new Error("Missed parameters: " + missed_required_params);
} else {
return params;
}
});
}
Node.js database result return late inside the function
const db = req.app.db;
function getFeaturebyID(featureids) {
db.planFeatures.findOne({"_id": featureids }).then(features => {
return features.planFeaturesTitle;
});
}
const planLists ={};
db.planManagement.find({}).toArray((err, planList) => {
// res.end(JSON.stringify(planList));
featurearray = [];
var j =1;
planList.forEach(function(row) {
planLists._id = row._id;
features = row.planFeatures.split(',');
for (let i = 0; i < features.length; i++) {
featurearray[i] = getFeaturebyID(features[i]);
// console.log(getFeaturebyID(features[i]));
}
//row.planFeaturesName[j] = featurearray;
console.log(featurearray);
j++;
});
//console.log(planList);
// res.end(JSON.stringify(req.session));
res.render('stylist/plan_selection', {
top_results: planList,
title: 'Schedule',
config: req.app.config,
session: req.session,
message: common.clearSessionValue(req.session, 'message'),
messageType: common.clearSessionValue(req.session, 'messageType'),
helpers: req.handlebars.helpers,
showFooter: 'showFooter'
});
});
});
return features.planFeaturesTitle; return a value late while calling the function. I try callback but not works
This is due to asynchronous nature of node.js,
First declare your function async like this,
const getFeaturebyID = async (featureids) => {
const features = await db.planFeatures.findOne({"_id": featureids });
return features.planFeaturesTitle;
}
Then use it like this,
planList.forEach(async (row) => {
// your code here
for (let i = 0; i < features.length; i++) {
featurearray[i] = await getFeaturebyID(features[i]);
}
// your code here
});