I'm trying to get the hang of using Mongoose promises with the async/await functionality of Node.js.
However I have problems with the second "find" function because is linked to the first one, i think because i dont have the first find result.
How can I wait for the response of the first function and then execute the second?
exports.permissions_Check2 = async function(params){
const Sessioni = require('../models/Sessioni');
const Permessi = require('../models/Permessi');
const express = require ('express');
var token= params['Token'];
var tabelle = params['Tabelle'];
var DataSession= [];
var out;
try{
const sessioni = await Sessioni.findOne({token: token}).exec();
const permessi = await Permessi.findOne({IDGruppo: sessioni.IDGruppo}).exec();
out={
IDAccesso: sessioni._id,
IDUser: sessioni.IDUser,
IDGruppo:sessioni.IDGruppo,
Permessi: permessi
}
return out;
} catch (err){
return err;
}
return out;
}
output:
{
IDAccesso: "ehwuhf7867tgyb",
IDUser: 1,
IDGruppo: 1,
Permessi: null }
What about using Promises?
That will look like
Sessioni.findOne({token: token})
.exec()
.then(sessioni => {
Permessi.findOne({IDGruppo: sessioni.IDGruppo})
.exec()
.then(permessi => {
out={
IDAccesso: sessioni._id,
IDUser: sessioni.IDUser,
IDGruppo:sessioni.IDGruppo,
Permessi: permessi
}
}).catch(e => throw e);
}).catch(e => throw e)
I'm not sure what DB you're using, but hope that will help
Related
I am using q and I have multiple mongoose .exec() promises that never gets to the .then() part of the code, so never allow the q to resolve. Can't figure out why it never comes back.
var defer = q.defer();
var promises = [];
console.log('Exams:', exams.length);
for (var e=0; e<exams.length; e++) {
console.log('Exams:', exams[e]._id);
var newPromise = Pupilexam.find({ _exam: exams[e]._id }).populate('_user').exec()
.then((pupils) => {
console.log("Adding pupils", exams[e]._id);
exams[e].pupils = pupils;
resolve(exams[e]);
})
.catch((err) => {
reject(err);
});
console.log(typeof newPromise);
promises.push(newPromise);
console.log("Promised pushed");
}
q.all(promises).then(function(data){
console.log("q'd all");
defer.resolve(res.status(200).json(exams));
});
return defer;
The Pupilexam.find().exec() never reaches the .then() so the promises never resolve and the defer never resolves. Why would the mongoose find not get to the .then()? What have I missed?
*** UPDATE ***
Even using the built in promises, we get the same issue. The Pupilexams.find() call never comes back.
var promises = [];
for (var e=0; e<exams.length; e++) {
console.log('e:', e);
console.log('Exam', exams[e]._id);
var newPromise = Pupilexam.find({ _exam: exams[e]._id }).populate('_user').exec()
.then((pupils) => {
console.log("Adding pupils", exams[e]._id);
exams[e].pupils = pupils;
})
.catch(handleError(res));
promises.push(newPromise);
}
Promise.all(promises).then((exams) => {
console.log(values);
res.status(200).json(exams)
});
With this method I also get a headers error on the call UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
** ADDITIONAL CODE REQUESTED **
function handleError(res, statusCode) {
statusCode = statusCode || 500;
return function(err) {
console.log(err.message);
res.status(statusCode).send(err);
};
}
To answer the updated question regarding the Cannot set headers after they are sent to the client error. Looks like you send a response to the client inside your handleError function. Now, if more than one Pupilexam.find call fails, handleError would be invoked twice, resulting in the mentioned error.
You should move the catch-handler down to the Promise.all call:
const promises = [];
for (const exam of exams) {
const newPromise = Pupilexam
.find({ _exam: exam._id }).populate('_user').exec()
.then((pupils) => {
exam.pupils = pupils;
});
promises.push(newPromise);
}
Promise.all(promises)
.then((exams) => {
res.status(200).json(exams);
})
.catch(handleError(res));
I guess that you are indeed returning your promise but you are returning an empty json.
There are 2 problems with your approach:
You are not returning from your then: should return pupils and it is returning undefined
You are logging values that I don't know what it is
.then((pupils) => {
console.log("Adding pupils", exams[e]._id);
exams[e].pupils = pupils;
// you should return something // return pupils
})
promises.push(newPromise);
Promise.all(promises).then((exams) => {
// ['undefined', 'undefined', ...]
console.log(values);
res.status(200).json(exams)
});
Looks like the answer was that on these two lines the exams[e] is not in scope, because by the time the promise comes back the loop has moved on, so e is wrong and gets too high so it was erroring.
console.log("Adding pupils", exams[e]._id);
exams[e].pupils = pupils;
Only discovered that when I read #eol's message about the catch and decided to catch it properly and output.
it is Look from your code.
//(async) function
for (var e of exams) {
try {
const pupils = await Pupilexam.find({ _exam: exams[e]._id
}).populate('_user').exec().lean()
e.pupils = pupils
}catch((err){
//handleError
};
}
res.status(200).json({data: exams})
maybe that will show you how match are you wrong
I have an array of addons and I want to insert them into the db table.
var addons = [sample,sample,.....]
return new Promise((resolve,reject) => {
addons.foEach(async addon => {
// first check if the items is in db
const response = await Kinex.where({}).from('table_name');
if(response.length == 0){
// insert new record
const insertResp = kinex('table_name').insert(addon)
addon.system_id = insertResp[0];
}else{
addon.system_id = response[0].id;
}
})
})
What I expected is to have unique record in the database, but the above code produced duplicate record in the database. Please help to find out the issue with the code.
The problem is running async function inside a loop. As mentioned by #Felix, forEach doesn't know about async functions and doesn't wait for your where query to return. If you wanna do things in async manner inside loops, you can do it with for..of loops. Also make sure to always use try/catch blocks while using async/await. Below is the code in your case:
const addons = [sample,sample,.....];
return new Promise(async (resolve, reject) => {
try {
for (let addon of addons) {
// first check if the items is in db
const response = await Kinex.where({}).from('table_name');
if (response.length) {
const insertResp = await kinex('table_name').insert(addon)
addon.system_id = insertResp[0];
} else addon.system_id = response[0].id;
resolve(); // resolve with whatever you wants to return
}
} catch (e) {
reject(e)
}
});
You can read more on for..of with async/await here.
As pointed by #Sándor, here's the code using Promise.all:
var addons = [sample, sample, .....]
return Promise.all(addons.map(async addon => {
// Do your async stuff here
// first check if the items is in db
const response = await Kinex.where({}).from('table_name');
if (response.length == 0) {
// insert new record
const insertResp = kinex('table_name').insert(addon)
addon.system_id = insertResp[0];
} else {
addon.system_id = response[0].id;
}
}))
This question already has answers here:
Using async/await with a forEach loop
(33 answers)
Closed last year.
I'm trying to fetch json, check with mongodb if duplicate exist and if not, then to insert data into mongodb.
The problem is loops goes very fast, without waiting for duplicate check and insert.
What am I doing wrong here?
const fetch = require('node-fetch');
var MongoClient = require('mongodb').MongoClient;
async function fetchPhotos() {
MongoClient.connect("mongodb://localhost:27017", async function (err, dbo) {
const db = dbo.db('mydb')
if (err) throw err;
for (var i = 1; i < 100; i++) {
await fetch(`domain.com/?page=${i}`)
.then(res => res.json())
.then((response) => {
response.forEach(photo => {
console.log("checking if there is duplicate: " + photo.id);
var exists = db.collection("photos").countDocuments({"id": photo.id}, {limit: 1});
if (exists === 1) {
console.log("dupl found, next!");
} else {
db.collection("photos").insertOne(photo, function (err, res) {
if (err) throw err;
console.log("1 document inserted");
});
}
});
});
}
});
}
module.exports.fetchPhotos = fetchPhotos;
There are a few problems with your asynchronous code inside a loop.
a .forEach() loop does not wait for await. You have to use a for loop or while loop if you want it to wait for await.
You aren't using await on db.collection("photos").countDocuments({"id": photo.id}, {limit: 1});.
You aren't using await on db.collection("photos").insertOne(photo).
Do not mix plain callbacks and promises in the same flow of control. It makes it very difficult to code safely and with proper error handling.
You are missing appropriate error handling in a number of places.
You can restructure the whole thing to use the promise interface to your database and then sequence the iteration through the photos and simplify things like this:
const fetch = require('node-fetch');
var MongoClient = require('mongodb').MongoClient;
async function fetchPhotos() {
const dbo = await MongoClient.connect("mongodb://localhost:27017");
const db = dbo.db('mydb');
for (let i = 1; i < 100; i++) {
let response = await fetch(`http://example.com/?page=${i}`);
let data = await response.json();
for (let photo of data) {
console.log("checking if there is duplicate: " + photo.id);
let cnt = await db.collection("photos").countDocuments({"id": photo.id}, {limit: 1});
if (cnt > 0) {
console.log("dupl found, next!");
} else {
await db.collection("photos").insertOne(photo);
console.log("photo inserted");
}
}
}
}
// caller of fetchPhotos() gets a promise that tells you if the
// operation completed or had an error
module.exports.fetchPhotos = fetchPhotos;
I need to call out to a function that runs a sql query, with row level functionality, and await the entire process before continuing.
Function code:
const sql = require('mssql')
exports.doit = ()=>{
const pool1 = new sql.ConnectionPool(dbConfig);
const pool1Connect = pool1.connect();
pool1.on('error', err => {
console.error('error occurred on pool')
})
await pool1Connect
try {
const request = pool1.request();
request.stream = true;
request.query('select * from dbo.user');
request.on('row', async orow => {
console.log('outer row');
const innerPool = new sql.ConnectionPool(dbConfig);
const innerConnection = innerPool.connect();
innerPool.on('error', err => {
console.error('error occurred on pool')
});
const iConnection = await innerConnection;
connections.push(iConnection);
const innerRequest = innerPool.request();
innerRequest.stream = true;
var iquery = 'select * from dbo.order where userId='+ orow.userId
innerRequest.query(iquery);
innerRequest.on('row', async irow => {
console.log(`User: ${orow.userId} Order: ${irow.orderId}`);
});
innerRequest.on('done', async () => {
console.log('inner done');
iConnection.close();
});
});
request.on('done', async () => {
console.log('outer done');
})
} catch (err) {
console.error('SQL error', err);
}
sql.on('error', err => {
// ... error handler
})
}
Then call the above function like this:
var doit = require('./testmeHandler.js').doit;
doit()
.then(()=>{
console.log("I AM DONE");
});
OR
await doit();
console.log('I AM DONE');
You get the idea...
But what is really happening is, the function gets called, then 'I AM DONE' and then the results of all the sql calls.
Can someone help me get 'I AM DONE' at the bottom? Still getting used to the async/await and promises.
Thanks
After quite a bit of time trying to get this to work synchronously from the caller I gave up and re-wrote the method to use the regular query (not streaming) and implemented my own paging/throttling as to control memory usage. It works great now!
I am using a connection pool to allow for sub queries and other processes to occur async within a batch of results.
I will post the updated code.
Somehow I believe you have jumbled it all up a bit.
Use this
exports.doit = async ()=>
{
const request = new sql.Request(conn)
let records = await request.query('select * from dbo.user')
records.forEach(async r=>{
try{
// do something
const inner = new sql.Request(conn)
let recordInner = await request.query(innerQuery)
recordInner.forEach(async r=>{//do some stuff})
inner.close()
}
catch(err){
//do something with the error
}
records.close()
})
}
The execution:
async execute(){
const result = await doit()
return result
}
execute()
Though I have no idea why you are using two connections at all . Just try writing a more defined query using JOIN OR WHERE subquery. You can achieve all this in a single query instead of a using nested connection. SQL though a bit old, it really is quite powerful.
select * from dbo.order WHERE userId IN (SELECT userId FROM dbo.user)
Makes more sense to me. But, whatever floats your boat.
More on sub-queries: https://www.dofactory.com/sql/subquery
I'm trying to export a variable in node.js like this:
let news = [];
const fetchNews = new Promise ((resolve, reject) => {
let query = 'SELECT id, name FROM news';
mysql.query(query, [], (error, results) => {
if (error)
reject({error: `DB Error: ${error.code} (${error.sqlState})`})
results = JSON.parse(JSON.stringify(results));
news = results;
resolve(results);
});
});
if(!news.length)
fetchNews
.then(results => {news = results})
.catch(err => {console.log('Unable to fetch news', err)});
exports.news = news;
When I use this code in some other module like this:
const news = require('./news.js').news;
console.log(news);
//returns [];
Can somebody point out my mistake in first code?
There are a couple of things that seem odd in the way you are doing this:
You have an async operation but you want just the value without actually awaiting on the operation to complete. Try something like this:
module.exports = new Promise ((resolve, reject) => {
mysql.query('SELECT id, name FROM news', (error, results) => {
if (error)
reject({error: `DB Error: ${error.code} (${error.sqlState})`})
resolve(JSON.parse(JSON.stringify(results)));
});
});
Then to get the news:
var getNewsAsync = require('./news')
getNewsAsync.then(news => console.log(news))
It would be cleaner/shorter if you actually utilize async/await with the mysql lib.
Update:
With Node 8 and above you should be able to promisify the mySQL lib methods. Although there might be better npm options out there to get this to work. Here is an untested version:
const mysql = require('mysql');
const util = require('util');
const conn = mysql.createConnection({yourHOST/USER/PW/DB});
const query = util.promisify(conn.query).bind(conn);
module.exports = async () => {
try {return await query('SELECT id, name FROM news')} finally {conn.end()}
}
To get the news:
var getNewsAsync = require('./news')
console.log(await getNewsAsync())