After a succesful query to Mongodb to get a list of news, for the news that have a link attached i search for link details in the database but after i set them inside the modified news object i cannot push it to an array. Why does this happen?
var newsarray = []
for(i=0;i<newsfound.length;i++){
if(!newsfound[i].link._id){
newsarray.push(newsfound[i])
} else {
var tempnew = newsfound[i];
db.findOne('links',{'_id':tempnew.link._id},function(err,linkdetails){
if(err){
console.log(err)
} else {
tempnew.linkdetails = linkdetails;
newsarray.push(tempnew)
}
})
}
}
console.log(newsarray)
The result of this is an array without the link containing news or if i try a few changes an array with the original news without the added details.
You can not use an asynchronous function inside a for loop. The reason is that the for loop gets executed before even any callback could come, and hence the scope gets messed up.
You should use recursive function (self calling) which will prevent the next async call before the previous is over.
var i = 0;
function fn() {
// your logic goes here,
// make an async function call or whatever. I have shown async in a timeout.
setTimeout(function () {
i += 1;
if (i < newsfound.length) {
fn();
} else {
// done
// print result
}
});
}
Update:
For your use case,
var newsarray = []
var i = 0;
function done() {
// done, use the result
console.log(newsarray);
}
function fn() {
if (!newsfound[i].link._id) {
newsarray.push(newsfound[i]);
i += 1;
if (i < newsfound.length) {
fn();
} else {
done();
}
} else {
var tempnew = newsfound[i];
db.findOne('links', {'_id':tempnew.link._id}, function(err, linkdetails){
if(err){
console.log(err)
} else {
tempnew.linkdetails = linkdetails;
newsarray.push(tempnew);
i += 1;
if (i < newsfound.length) {
fn();
} else {
done();
}
}
})
}
}
Related
I have this piece of code
let promiseList = []
for (let i in data) {
let promise = checkIfMember(data[i].tg_id, chatId).then(res => {
if (res) {
//if the user has a undefined username it won't be rained
if (data[i].username != "undefined") {
console.log(data[i].username)
members.push([data[i].tg_id, data[i].username])
}
}
}).catch(err => {
console.log(err)
})
promiseList.push(promise)
}
return Promise.all(promiseList).then((res) => {
//list of members that are in the room , we randomize it before returning
shuffleArray(members)
if(numberOfUsers > members.length){
return[false, members.length]
}else{
members = members.slice(0,numberOfUsers)
return [true, members]
}
});
Basically I have a promise list that is being filled. And then all of them are executed with a promiseAll. The problem is that I dont want all of them to execute, I want to to do something like this:
let promiseList = []
let validmembers = 0;
for (let i in data) {
let promise = checkIfMember(data[i].tg_id, chatId).then(res => {
if (res) {
//if the user has a undefined username it won't be rained
if (data[i].username != "undefined") {
console.log(data[i].username)
members.push([data[i].tg_id, data[i].username])
//stop there the execution
validmembers++;
if(validmembers == numberOfUsers){
return;
}
}
}
}).catch(err => {
console.log(err)
})
promiseList.push(promise)
}
return Promise.all(promiseList).then((res) => {
//list of members that are in the room , we randomize it before returning
shuffleArray(members)
if(numberOfUsers > members.length){
return[false, members.length]
}else{
members = members.slice(0,numberOfUsers)
return [true, members]
}
});
But the problem is that the promises are async, so the promiselist filling doesnt stop.
How would I solve this?
It appears you want the members array to have no more than numberOfUsers entries in it due to the promises. Since the promises run asynchronously you can't stop the checkIfMember function from being called, but inside of its then function you could avoid accumulating more members like this:
// don't use `!== "undefined"` unless it can actually be the string "undefined"
if (data[i].username) {
if (members.length < numberOfUsers) {
console.log(data[i].username);
members.push([data[i].tg_id, data[i].username]);
}
}
By only pushing to members when it's not yet full you will avoid adding more than numberOfUsers and don't need to do the slice later.
If instead you want to avoid the entire promise work when enough have been collected, then you can serialize them like this:
async function yourFunction() {
for (let i in data) {
if (members.length < numberOfUsers) {
// don't continue to the next 'i' until this one is done
await checkIfMember(data[i].tg_id, chatId)
.then(res => {
if (res) {
//if the user has a undefined username it won't be rained
if (data[i].username != "undefined") {
console.log(data[i].username);
members.push([data[i].tg_id, data[i].username]);
}
}
})
.catch(err => {
console.log(err);
});
} else {
break; // no need to continue once members is full
}
}
return [true, members];
}
Update !!
I fixed my initial issue with the help of Dacre Denny answer below however when writing tests for my code it turned out that the changes were not being saved before the server responded therefor the company collection in my test database was empty, I fixed this issue with the following code
Companies.find({ company_name: company.company_name }).then(found => {
if (found.length !== 0) {
return res.status(400).json({ error: "Company already exists" });
}
var userForms = company.users;
company.users = [];
const finalCompany = new Companies(company);
console.log(finalCompany);
var userPromises = [];
for (var x = 0; x < userForms.length; x++) {
var user = userForms[x].user;
user.company = finalCompany._id;
userPromises.push(userCreation(user));
}
return Promise.all(userPromises).then(responses => {
for (var x in responses) {
if (!responses[x].errors) {
finalCompany.addUser(responses[x]._id);
} else {
res.status(400).json(responses[x]);
}
}
return finalCompany;
});
})
// I moved the save in here !!!
.then((finalCompany) => {
finalCompany.save().then(()=>{
res.status(200).json({signup:"Successful"});
})
},(err) => {
res.json({error: err});
});
});
Original Issue
I am trying to create a mongoose document to represent a company, this code saves the model in my db however it does not seem to be responding with a status code or reply to postman when I make a request
I've used a debugger to step through the code but I am very rusty on my JS and I am afraid I've gone into deep water with promises thats gone over my head.
router.post('/c_signup', auth.optional, (req, res, next) => {
const { body: { company } } = req;
var error_json = cbc(company);
if( error_json.errors.length > 0 ){
return res.status(422).json(error_json);
}
Companies.find({company_name: company.company_name})
.then((found) => {
if (found.length !== 0) {
return res.status(400).json({error: "Company already exists"});
}
var userForms = company.users;
company.users = [];
const finalCompany = new Companies(company);
var userPromises = [];
for (var x =0; x < userForms.length; x ++) {
var user = userForms[x].user;
user.company = finalCompany._id;
userPromises.push(userCreation(user));
}
Promise.all(userPromises).then((responses) => {
for (var x in responses){
if (!responses[x].errors){
finalCompany.addUser(responses[x]._id);
}
else {
res.status(400).json(responses[x]);
}
}
console.log("h2");
finalCompany.save(function () {
console.log("h3");
return res.status(200);
});
})
});
return res.status(404);
});
This is the output from the debug but the execution is hanging here
h2
h3
There are a few issues here:
First, the save() function is asynchronous. You'll need to account for that by ensuring the promise that save() returns, is returned to the handler that it's is called in.
The same is true with the call to Promise.all() - you'll need to add that promise to the respective promise chain by returning that promise to the enclosing handler (see notes below).
Also, make sure the request handler returns a response either via res.json(), res.send(), etc, or by simply calling res.end(). That signals that the request has completed and should address the "hanging behaviour".
Although your code includes res.json(), there are many cases where it's not guaranteed to be called. In such cases, the hanging behaviour would result. One way to address this would be to add res.end() to the end of your promise chain as shown below:
Companies.find({ company_name: company.company_name }).then(found => {
if (found.length !== 0) {
return res.status(400).json({ error: "Company already exists" });
}
var userForms = company.users;
company.users = [];
const finalCompany = new Companies(company);
var userPromises = [];
for (var x = 0; x < userForms.length; x++) {
var user = userForms[x].user;
user.company = finalCompany._id;
userPromises.push(userCreation(user));
}
/* Add return, ensure that the enclosing then() only resolves
after "all promises" here have completed */
return Promise.all(userPromises).then(responses => {
for (var x in responses) {
if (!responses[x].errors) {
finalCompany.addUser(responses[x]._id);
} else {
res.status(400).json(responses[x]);
}
}
console.log("h2");
/* Add return, ensure that the enclosing then() only resolves
after the asnyc "save" has completed */
return finalCompany.save(function() {
console.log("h3");
return res.status(200);
});
});
})
.then(() => {
res.end();
},(err) => {
console.error("Error:",err);
res.end();
});
Hey I'm trying to understand functional programming, stay current etc.
I have this gigantic nested node function tha tI'm attempting to refactor into modules. Each function passes an argument to the next, some are async api calls. I've gotten as far as breaking it down into multiple functions but they're still not really modular as each one calls the next function.
I'm wondered if there's a design pattern to totally untangle them so that the names of the other functions don't appear in the functions but can be passed as callbacks or something. Or maybe that's not even appropriate in this case?
I wrote some simpler fake code that approximates my actual problem so you don't have to sift through endless irrelevant specifics:
function1Async();
function function1Async() {
var theArray = [];
var theData = "";
var theInfo = "";
Async.get( /* api */, function(error, data, response) {
if (error) {
function4(); // function call
}
theData = data[0].infos;
for (i in data) {
theInfo = theData[i].info;
theArray.push(theInfo);
}
function2Async(theArray); // function call
});
}
function function2Async(array) {
var theArray = [];
var theObject = {}
var arrayLength = array.length;
for (let i = 0; i < arrayLength; i++) {
search = '"' + array[i] + '"';
T.get(/* api */, {q: trend, search: 50}, function (error, data, response) {
if (error) {
theArray.push("error");
}
else {
theObject = {
"data": data
}
theArray.push(theObject);
}
if (theArray.length == arrayLength) {
function3(theArray); // function call
}
});
}
}
function function3 (array) {
var theArray = array;
if (theArray.includes("error") == true) {
function5(); // function call
}
else {
function4(theArray); // function call
}
}
function function4(array) {
var file = 'files/data.json';
jsonfile.writeFile(file, array, function(err) {
function5(); // function call
});
}
function function5() {
var file = 'files/data.json';
jsonfile.readFile(file, function(err, obj) {
return res.json(obj);
});
}
Feel free to chime in with any suggestions even if they're not totally related to the question. Like I said I'm just trying to understand this stuff altogether. Thanks.
I have an array of urls like this
var urls = ["www.google.com", "www.yahoo.com"];
And I want to loop though the urls and perform an async task inside the loop and not move on to the next item until the async task has finished. I know you can do this with promises but I have having some trouble with it. Here what I have
var xmlReader = require('cloud/xmlreader.js');
function readResponse_async(xlmString) {
var promise = new Parse.Promise();
xmlReader.read(xlmString, function (err, res) {
if(err) {
promise.reject(err);
} else {
promise.resolve(res);
}
});
return promise;
}
for (i = 0; i < urls.length; i++) {
Parse.Cloud.httpRequest({
url: unionUrls[i],
}).then(function(httpResponse) {
try {
// console.log(httpResponse.text)
return readResponse_async(httpResponse.text)
} catch (e) {console.log(e)}
}
But right now it doesn't wait for the readResponse_async to finish, how can I have it wait for that?
Thanks
EDIT
After reading the response I make a save to my database and I have another array like this
var location = ['USA', 'England'];
And I make the save like this
function saveLoc_async(data, location) {
var i3, i4, i5, m,
TestItem = Parse.Object.extend("TestItem"),//can be reused within the loops?
promise = Parse.Promise.as();//resolved promise to start a long .then() chain
for (i3 = 0; i3 < data.count(); i3++) {
(function(testItem) {
testItem.set("item", data.at(i));
testItem.set("location", location);
//build the .then() chain
promise = promise.then(function() {
return testItem.save();
});
})(new TestItem());
//************************
//CALL retry(); here?
//**************************
}
Because with your answer I have
function retry() {
if (urlsUnion.length > 0) {
var nextUrl = urlsUnion.pop();
//********** ADDED LINE
var nextLoc = location.pop();
Parse.Cloud.httpRequest({
url: nextUrl,
}).then(function(httpResponse) {
xmlReader.read(httpResponse.text, function (err, res) {
if(err) {
// show an error
} else {
//********** ADDED LINE
saveLoc_async(res, nextLoc);
retry();
}
});
});
}
}
SO where should retry(); go because right now with the save sometimes it puts the second location with one of the first items url? why would that happen?
I did something similar to this for an animation.
var actions = [drawXXX, fadeOutYYY, drawXYZ];
this.startAnimation = function () {
actions.reduce(function (previousAction, nextAction) {
return previousAction.then(nextAction)
}, $.when());
}
Your code fires both urls immediately, and does not wait in-between.
What you would have to do is to remove the first url from the array and fire it. In the 'then' branch check if you still have url's in the array and repeat.
Like this (untested, edited to make the code clean again):
var xmlReader = require('cloud/xmlreader.js');
function readResponse_async(xlmString) {
xmlReader.read(xlmString, function (err, res) {
if(err) {
// show an error
} else {
readFirstUrl();
}
});
}
function readFirstUrl() {
if (urlsUnion.length == 0) {
return;
}
var url = urlsUnion.pop();
Parse.Cloud.httpRequest({
url: url,
}).then(function(httpResponse) {
readResponse_async(httpResponse.text);
});
}
readFirstUrl();
Not sure I understand your use of unionUrls array, but if you have your URL's in a urls array, I think this is pretty clean:
function getUrl(url) {
return Parse.Cloud.httpRequest(url)
.then( function(httpResponse) {
return readResponse_async(httpResponse.text);
});
}
urls.reduce( function(prev, url) {
return prev ? prev.then( function() { getUrl(url); }) : getUrl(url);
}, null);
So I am stumped, and just cannot seem to grasp what is going on. I have a function that takes an array of orders.
var collection = [{ordernumber: 1, href: 'FileDetails.aspx?FileId=1234'},
{ordernumber: 2, href: 'FileDetails.aspx?FileId=1478'}];
var OrdersListToImport = [];
function loopOrders(collection, callback) {
for(var i = 0; i < collection.length; i++) {
console.log('processing order #: ' + collection[i].ordernumber);
var answersReturned = 0;
db.needsImported(collection[i].ordernumber, function(answer) {
if (answer) {
OrdersListToImport.push(collection[i]);
//console.log(collection[i]);
}
if (++answersReturned == collection.length) {
callback();
}
});
}
}
NeedsImported function as follows:
needsImported: function(ordernumber, callback) {
pool.query('Select controlnumber From orders Where ordernumber = ?', [ordernumber], function(err, result) {
if (!err) {
if (result.length == 0) {
callback(true);
}
else {
callback(false);
}
}
});
}
When inside the callback function of db.needsImported, collection[i] becomes undefined. It was driving me mad, so i made a little sample file to see if there was a reason I couldn't access an argument from inside a callback function. It works as expected, only pushing even numbers. here is the sample:
var nums = [];
var collection = [1,2,3,4,5,6,7,8,9,10];
displayValue(collection, function() {
});
console.log(nums);
function displayValue(col, callback) {
for(var i = 0; i < col.length; i++) {
sleep(col[i] * 500, function() {
console.log('Count: ' + col[i]);
if (col[i] % 2 == 0) {
nums.push(col[i]);
}
});
callback();
}
}
function sleep(time, callback) {
var stop = new Date().getTime();
while(new Date().getTime() < stop + time) {
;
}
callback();
}
I hope someone can help me to understand what I am doing wrong.
You might see more clearly what the problem is if you were to console.log(i) in the spot where you expect collection[i] to not be undefined.
What's going on in your for loop is you're iterating through your array and firing off multiple asynchronous tasks. When the loop is finished, the value of i is 2. i is a closed variable accessible to your callbacks, but remember the asynchronous timing here, your needsImported callbacks are all getting invoked after your for loop has completed, so naturally, collection[2] is undefined. To fix it you could just get rid of the index and use Array.forEach instead:
function loopOrders(collection, callback) {
var answersReturned = 0;
collection.forEach(function(item, index) {
needsImported(item.ordernumber, function(answer) {
console.log('index:', index);
if (answer) {
OrdersListToImport.push(item);
}
if (++answersReturned == collection.length) {
callback();
}
});
});
}
Note also that if you do need to keep track of the index in your callback, you can receive it as the second parameter in your forEach callback as I've done above.
One more note :) There's a significant flaw in this code:
needsImported: function(ordernumber, callback) {
pool.query('Select controlnumber From orders Where ordernumber = ?', [ordernumber], function(err, result) {
if (!err) {
if (result.length == 0) {
callback(true);
}
else {
callback(false);
}
}
});
}
If an err does occur, you're ignoring it, but worse than that, you're not invoking the callback. Confusing bugs will emerge from this. It's common practice in node to serve an err var as the first argument of a callback, so in a success scenario you would do this callback(null, true).