var veh = [];
app.get('/updateProf', isLoggedIn, function(req, res) {
for (var i = 0; i < req.user.local.vehicles.length; i++){
Vehicles.findById(req.user.local.vehicles[i], function(err, vehicle) {
veh.push(vehicle);
console.log("GET Json: " + veh);
});
}
console.log(veh);
res.json(veh);
veh.length = 0;
});
So I am doing a get request to obtain all my vehicles that a user owns and return its json, it works fine after a refresh, but when I go to the page it shows a empty array on the initial load, if I refresh the page, the array is populated. I think the issue is something to do with it being asynchronous but I'm having a hard time thinking this way and need some advice on how to tackle this.
Yes!!
You will have to wait for all of the callbacks to finish before returning the JSON.
A solution is to keep a count of how many callbacks have been executed and when all of them have been executed you can return the JSON.
var veh = [];
app.get('/updateProf', isLoggedIn, function(req, res) {
number_processed = 0;
total = req.user.local.vehicles.length;
for (var i = 0; i < req.user.local.vehicles.length; i++){
Vehicles.findById(req.user.local.vehicles[i], function(err, vehicle) {
if(!err){
veh.push(vehicle);
}
number_processed = number_processed + 1;
if(number_processed === total){
res.json(veh);
}
console.log("GET JSON: " + veh);
});
}
veh.length = 0;
});
If you are using a more recent version of Mongoose, then you can directly use Promises that are returned by Mongoose for each query.
For example, your query can be simplified to
Vehicles.find({ _id: {'$in': req.user.local.vehicles }})
.exec()
.then(function(vehicleArr) {
res.json(vehicleArr);
});
Note that I use the $in operator to directly translate your loop into an IN condition, which takes an array of what you want to compare (in this case, it's an array of IDs)
The then() function just executes on completion of the query.
Async is a utility library to deal with this.
var async = require('async');
app.get('/updateProf', isLoggedIn, function(req, res) {
async.map(req.user.local.vehicles, function(vehicle, cb){
Vehicles.findById(vehicle, function(err, vehicle) {
if (err) cb(err, null);
console.log('GET Json: ' + vehicle);
cb(null, vehicle);
});
}, function (err, results) {
console.log(results);
res.json(results);
});
});
Related
I've been pointed towards using the async module, but I'm not quite sure how to use waterfall to solve my problem.
My original code had problems with asynchronicity.
var Image = require('./models/image');
var User = require('./models/user');
var query = Image.find({});
query.limit(10);
query.sort('-date')
query.exec(function (err, collected) {
if (err) return console.error(err);
var i = 0;
var authors = [];
while (i < 8) {
var search = User.find({'twitter.id' : collected[i].author});
search.exec(function (err, user){
if (err) return console.error(err);
var result = (user[0].twitter.username);
authors.push(result);
});
i = i + 1;
}
}
console.log(authors);
I want the authors array to hold all the found usernames. However when that last console.log() call returns '[]'
So, you want to wait for all of the searches to complete first. You should put all your async calls into an array, and then use an async library to chain them together (waterfall) or execute simultaneously (parallel). Parallel tends to execute "faster":
var searches = [];
while (i < 8) {
var search = User.find({'twitter.id' : collected[i].author});
searches.push(function(cb) {
search.exec(function (err, user){
if (err) cb(err, null);
else cb(null, user[0].twitter.username);
});
});
i++;
}
async.parallel(searches, function( err, authors ) {
if ( err ) return console.error( err );
console.log(authors);
// Authors only defined here.
// TODO: More code
});
// Authors not defined here.
I have a strange problem, when I push my result in my array, the result isn't at the right position in my array (for example the result instead of being at the index number 1 is at the index 3), and when I re-run my module results change of position randomly in the array .
var cote = function(links, callback) {
var http = require('http');
var bl = require('bl');
var coteArgus = [];
for (i = 0; i < links.length; i ++) {
http.get('http://www.website.com/' + links[i], function(response) {
response.pipe(bl(function(err, data) {
if (err) {
callback(err + " erreur");
return;
}
var data = data.toString()
newcoteArgus = data.substring(data.indexOf('<div class="tx12">') + 85, data.indexOf(';</span>') - 5);
myresult.push(newcoteArgus);
callback(myresult);
}));
});
}
};
exports.cote = cote;
The problem lies in the fact that although the for is synchronous the http.get and the pipe operation are not (I/O is async in nodejs) so the order of the array depends on which request and pipe finishes first which is unknown.
Try to avoid making async operations in a loop, instead use libraries like async for flow control.
I think this can be done in the right order, using async map
Here a sample with map and using request module.
// There's no need to make requires inside the function,
// is better just one time outside the function.
var request = require("request");
var async = require("async");
var cote = function(links, callback) {
var coteArgus = [];
async.map(links, function(link, nextLink) {
request("http://www.website.com/" + link, function(err, response, body) {
if (err) {
// if error so, send to line 28 with a error, exit from loop.
return nextLink(err);
}
var newcoteArgus = body.substring(
body.indexOf("<div class='tx12'>") + 85,
body.indexOf(";</span>") - 5
);
// pass to next link, and add newcoteArgus to the final result
nextLink(null, newcoteArgus);
});
},
function(err, results) {
// if there's some errors, so call with error
if(err) return callback(err);
// there's no errors so get results as second arg
callback(null, results);
});
};
exports.cote = cote;
One more thing, i'm not sure, really what you are doing in the part where you search html content in the responses but there's a really good library to work with JQuery selectors from server side maybe can be useful for you.
Here's how you should call the function
// Call function sample.
var thelinks = ["features", "how-it-works"];
cote(thelinks, function(err, data) {
if(err) return console.log("Error: ", err);
console.log("data --> ", data);
});
I am trying to push some values to array by fetching data from Jenkins APIs, like below.
buildNum = 14;
async.waterfall([
function(callback){
for ( var i = buildNum; i > (buildNum-5); i--) {
(function(){
jenkins.build_info('BuildDefinitionRequest', i, function(err, data) {
if (err){ return console.log(err); }
var tmpObj = {};
tmpObj.jobID = data.fullDisplayName;
tmpObj.result = data.result;
tmpObj.dateTime = data.id;
console.log(tmpObj);
finalArray.push(tmpObj);
});
})();
}
callback(null, finalArray, 1);
},
function(finalArray, value, callback){
console.log(finalArray, value);
callback(null, 'done');
}
],function(err, result){
});
But "callback(null, finalArray, 1);" is getting called before the for loop finish its execution.
When I am printing the value of "finalArray" inside the for loop I am able to see all the values.
Technically the for loop has finished executing, but the jenkins.build_info calls haven't. You cannot make async calls inside of a for loop like that and expect the for loop to only finish after all the calls are complete. You're already using async, so this is an easy fix. I would do something like this:
var buildNum = 14;
var builds = [];
// just builds a collection for async to operate on
for(var i = buildNum; i > (buildNum - 5); i--) {
builds.push(i);
}
var finalArray = [];
async.each(builds, function(build, next) {
jenkins.build_info('BuildDefinitionRequest', build, function(err, data) {
if (err) { next(err); }
var job = {
jobID: data.fullDisplayName,
result: data.result,
dateTime: data.id
};
finalArray.push(job);
next();
});
}, function(err) {
// this won't be called until all the jenkins.build_info functional have completed, or there is an error.
console.log(finalArray);
});
How do you access mongodb count results in nodejs so the result can be accessible to the asynchronous request? I can get the result and update the database but the asynchronous request fails to access the vars or the vars are empty and the vars appear to be updated when the next asynchronous request is made. The request must not be waiting for the query to finish and the next request is filled with the previous request's variables.
testOne.increment = function(request) {
var MongoClient = require('mongodb').MongoClient,
format = require('util').format;
MongoClient.connect('mongodb://127.0.0.1:27017/bbb_tracking', function(err, db) {
if (err) throw err;
collection = db.collection('bbb_tio');
collection.count({vio_domain:dom}, function(err, docs) {
if (err) throw err;
if (docs > 0) {
var vio_val = 3;
} else {
var vio_val = 0;
}
if (vio_val === 3) {
event = "New_Event";
var inf = 3;
}
db.close();
console.log("docs " + docs);
});
});
};
In the above, even when the vars are set in scope they are not defined asynchronously. Can I get some guidance on structuring this properly so the vars are populated in the callback. Thank you!
Since the count function is asynchronous, you'll need to pass a callback to the increment function so that when the count is returned from the database, the code can call the callback.
testOne.increment = function(request, callback) {
var MongoClient = require('mongodb').MongoClient,
format = require('util').format;
MongoClient.connect('mongodb://127.0.0.1:27017/bbb_tracking', function(err, db) {
if (err) throw err;
var collection = db.collection('bbb_tio');
// not sure where the dom value comes from ?
collection.count({vio_domain:dom}, function(err, count) {
var vio_val = 0;
if (err) throw err;
if (count > 0) {
vio_val = 3;
event = "New_Event";
var inf = 3;
}
db.close();
console.log("docs count: " + count);
// call the callback here (err as the first parameter, and the value as the second)
callback(null, count);
});
});
};
testOne.increment({}, function(err, count) {
// the count would be here...
});
(I don't understand what the variables you've used mean or why they're not used later, so I just did a bit of a clean-up. Variables are scoped to function blocks and hoisted to the function, so you don't need to redeclare them in each if block like you had done with vio_val).
You could use the 'async' module. It makes the code a lot cleaner and easier to debug. Take a look at the code in GitHub for adduser.js & deleteuser.js in the following post
http://gigadom.wordpress.com/2014/11/05/bend-it-like-bluemix-mongodb-using-auto-scaling-part-2/
Regards
Ganesh
length give you count of result array
const userdata = await User.find({ role: role, 'name': new RegExp(searchkey, 'i') },{date: 0,__v:0,password:0}).
sort(orderObj)
.limit(limit)
.skip(skip);
console.log(userdata.length);
Below is a snapshot of my code from routes/index.js
exports.index = function(req, res){
var results=new Array();
for(var i=0; i<1000;i++){
//do database query or time intensive task here based on i
// add each result to the results array
}
res.render('index', { title: 'Home !' , results:results });
};
If I run this code , due to the asynchronous nature of javascript the last line gets executed before the loop gets completely processed . Hence my webpage doesnt have the results . How do I structure this such a way that the page gets loaded once the queries are completed ?
Updated
Inside the loop I have database code ( Redis ) like the below -
client.hgetall("game:" +i, function(err, reply) {
results.push(reply.name);
});
Use the async library:
exports.index = function(req, res){
var results=new Array();
async.forEach(someArray, function(item, callback){
// call this callback when any asynchronous processing is done and
// this iteration of the loop can be considered complete
callback();
// function to run after loop has completed
}, function(err) {
if ( !err) res.render('index', { title: 'Home !' , results:results });
});
};
If one of the tasks inside the loop is asynchronous, you need to pass the asynchronous task a callback that calls callback(). If you don't have an array to use in forEach, just populate one with integers 1-1000.
Edit: Given your latest code, just put the async callback() right after responses.push(reply.name).
exports.index = function(req, res) {
var events = require("events");
var e = new events.EventEmitter();
e.expected = 1000;
e.finished = 0;
e.results = [];
e.on("finishedQuery", (function(err, r) {
this.finished += 1;
this.results.push(r && r.name);
if (this.finished === this.expected) {
res.render('index', { title: 'Home !' , results:this.results });
};
}).bind(e));
for (var i = 0; i < e.expected; i++) {
client.hgetall("game:" + i, function(err, reply) {
e.emit("finishedQuery", err, reply);
});
};
};
Of course, the above code doesn't handle [1 or more] errors. You'd need to add logic that only responds (1) on the first error or (2) if no errors occur.