I've got an Express GET request that pulls data from a Mongoose query and for each doc returned, external functions perform calculations on each doc passed as x and return the results so I can render them on the front-end using Handlebars. Ideally, I would like to carry out my calculations calcA, calcB, calcC, calcD and then once they're completed for each of the documents, render the test-env.hbs template. Currently, the page doesn't render when I call it, in the logs, after some time, it shows GET /test-env - - ms - -, presumably because the callback gets stuck somewhere.
Express GET Request
var updates = require('./updates.js');
app.get('/test-env', function(req, res, next){
Market.find({"marketname" : 'To Win'})
.then(function(doc){
async.forEach(doc, function(x, callback){
updates.calcA(x);
updates.calcB(x);
updates.calcC(x);
updates.calcD(x);
}, function(err){
if(err)
return console.log(err);
res.render('test-env', {title: 'Test Page', items: doc});
});
});
});
Typical calc Function
I want to add returnA and returnB to the docs data so I can render it in an {{#each}} expression in Handlebars
calcA: function(x) {
Market.find({"student": x.student, "marketname": x.marketname})
.sort({btotal: -1})
.limit(1)
.then(function(ret) {
var valueA = ret[0].btotal;
var valueB = ret[0].back;
Market.find({"student": x.student, "marketname": x.marketname, "back": {$lt: valueB}})
.sort({odds: -1})
.limit(1)
.then(function(doc) {
var res = doc[0];
if (res == null) {
x.returnA = 0;
x.returnB = 0;
} else {
x.returnA = res.back;
x.returnB = res.btotal;
}
});
});
}
You aren't calling your callback in your async iterator. If the calc functions are asynchronous, those callbacks should be handled individually. If they are not asynchronous, a normal forEach will do the trick.
...
async.forEach(doc, function(x, callback){
updates.calcA(x);
updates.calcB(x);
updates.calcC(x);
updates.calcD(x);
callback(); // Call the callback to move on to the next item
}, function(err){
if(err)
return console.log(err);
res.render('test-env', {title: 'Test Page', items: doc});
});
...
It looks as if you're not actually calling your callback function.
async.forEach(doc, function(x, callback){
updates.calcA(x);
updates.calcB(x);
updates.calcC(x);
updates.calcD(x);
// <--- callback() needs to go here.
}
Look at: http://caolan.github.io/async/docs.html#each
The example shows you need to explicitly call the callback() function.
By the way, do your calculations (and the callback function) depend on the order of the contents of the doc collection? Because the async.forEach method actually does not guarantee that each of the elements in doc are going to be calculated in the same order as they are in the collection. So if you are, then it's worth considering if an out of order calculation may result in a different result.
Related
Hello guys I am trying to manipulate the documents that I am inserting to my collection with the create().Essentially I am calling a function that increments a letter field.
My pre hook is like
baseAttribute.pre('save',async function(next){
var att=this;
const query=await mongoose.models.BaseAttributes.find({},{},{sort:{_id:-1}}).limit(1)
console.log(query)
if(query.length===0)
{
att.code="AA"
}else{
att.code= Codes.GetAlphaCode(query[0].code);
}
next()
})
The result is that all the documents inserted by the create function are getting the same code
I found a solution to the problem.
// asyncs because I am not sure if it will cause a conflict with my async functions
var asyncs = require("async");
asyncs.eachOfSeries(newArray,function (item, i, next){
// console.log(item)
console.log("In each async")
// item.save(next);
BaseAttribute.find({},{},{sort:{_id:-1}}).limit(1).then(result=>{
console.log("In find")
if(!result[0]){
item.code="AA"
}else{
item.code=Codes.GetAlphaCode(result[0].code)
}
item.save(next);
})
}, function(err) {
if (err) return console.log(err);
res.json({done:"true"})
});
This is the way save documents one by one (in a serial order).
I query one collection (messages) with mongoose. The result is an array of documents. Each document contains an ID for a different collection (users). Now I want to query the users collection for each ID from the messages collection.
The idea is to update each message object with the information from the user collection before returning it to the front end.
I tried using async.each. For some reason the final function is never called even though I am making sure the callback() function is called after each iteration.
app.get('/getmsg', function(req, res){
messages.find({query})
.exec(function(err, ms){
if(err) throw err;
async.each(ms, function(m, callback){
users.findOne({_id : m.userId})
.lean()
.exec(function(err, user){
if(err) {
console.log('error' , err);
callback();
} else {
m.userName = user.name;
// everything is working up to here
callback();
}
}), function(err){
res.send(ms); // this is never returned!
}
});
});
});
Is there a better way of achieving this? I assume this must be a common issue.
Thanks!
You can't use res.send. Instead create a function to get notified about it. Something like this.
// 1st para in async.each() is the array of items
async.each(items,
// 2nd param is the function that each item is passed to
function(item, callback){
// Call an asynchronous function, often a save() to DB
item.someAsyncCall(function (){
// Async call is done, alert via callback
callback();
});
},
// 3rd param is the function to call when everything's done
function(err){
// All tasks are done now
doSomethingOnceAllAreDone();
}
);
Hej, have a problem. Trying to send Express response with Mongo data in it.
This is code from my Express server
var Task = require('./modules/Task');
app.get('/get-all-tasks',function(req,res){
res.setHeader('Content-Type', 'application/json');
console.log(Task.getAllTasks()); // returns undefined
res.json({msg:"Hej, this is a test"}); // returns object
});
This is mongoose model in separate file
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/todo-app');
var TaskSchema = mongoose.Schema({
name: String,
assignee: String
},{ collection : 'task' });
var Task = module.exports = mongoose.model('Task', TaskSchema);
module.exports.createTask = function (newTask, callback) {
newTask.save(callback);
}
module.exports.getAllTasks = function(){
Task.find().lean().exec(function (err, docs) {
console.log(docs); // returns json
});
}
How can I properly send data from getAllTasks function?
That's looks correct, but your are forgetting about the Javascript's asynchronous behavior :). When you code this:
module.exports.getAllTasks = function(){
Task.find().lean().exec(function (err, docs) {
console.log(docs); // returns json
});
}
You can see the json response because you are using a console.log instruction INSIDE the callback (the anonymous function that you pass to .exec())
However, when you type:
app.get('/get-all-tasks',function(req,res){
res.setHeader('Content-Type', 'application/json');
console.log(Task.getAllTasks()); //<-- You won't see any data returned
res.json({msg:"Hej, this is a test"}); // returns object
});
Console.log will execute getAllTasks() function that doesn't return anything (undefined) because the thing that really returns the data that you want is INSIDE the callback...
So, to get it work, you will need something like this:
module.exports.getAllTasks = function(callback){ // we will pass a function :)
Task.find().lean().exec(function (err, docs) {
console.log(docs); // returns json
callback(docs); // <-- call the function passed as parameter
});
}
And the we can write:
app.get('/get-all-tasks',function(req,res){
res.setHeader('Content-Type', 'application/json');
Task.getAllTasks(function(docs) {console.log(docs)}); // now this will execute, and when the Task.find().lean().exec(function (err, docs){...} ends it will call the console.log instruction
res.json({msg:"Hej, this is a test"}); // this will be executed BEFORE getAllTasks() ends ;P (because getAllTasks() is asynchronous and will take time to complete)
});
I believe what you would need to do is return the docs in your getAllTasks function, but perhaps a better way to do it asynchronously using callbacks like so:
module.exports.getAllTasks = function(callback){
Task.find().lean().exec(function (err, docs) {
// If there is an error, return the error and no results
if(err) return callback(err, null)
// No error, return the docs
callback(null, docs)
});
}
And then inside your route you would do:
app.get('/get-all-tasks',function(req,res){
Task.getAllTasks(err, docs){
if(err) return res.json(error: err)
res.json(msg: docs);
}
});
I'm not sure if getAllTasks should be a mongoose static, in which case your model would look something like this:
TaskSchema.statics.getAllTasks = function (callback) {
return this.find().lean().exec(callback);
}
I need to edit a Game object by adding a User object to it. This is done by the mongoose query findById. This query works. But however, when I want to add the modified game to the resulting array, something goes wrong. The 'console.log(game);' returns the right output, but the 'console.log(result);' is always empty. What is going wrong? Is it something with inner functions?
var result = [];
games.forEach(function(game){
User.findById(game.user1_id, function(err, user){
if(err)
console.log(err);
game.user1 = user;
result.push(game);
console.log(game);
});
});
console.log(result);
You have run into a class callback problem. When you call forEach on games the code will actually continue outside the callback and the result will therefore be the value you first assigned to it, which is []. This is due to the code being evaluated asynchronous.
Solve this by moving your code into a function with a callback that is called when the loop is done, like this:
var utils = require('restberry-utils');
var getResult = function(next) {
var result = [];
utils.forEachAndDone(games, function(game, iter) {
User.findById(game.user1_id, function(err, user) {
if (err) console.log(err);
game.user1 = user;
result.push(game);
iter();
});
}, function() {
next(result);
});
};
getResult(function(result) {
console.log(result);
});
Notice I've imported the restberry-utils package and used the forEachAndDone method. This method will loop through the objects but won't continue unless you call the iter method. When it has looped through all the objects, the last callback is called which is where I'm returning the result.
Hope this makes sense.
How do I set a variable to a query? I am trying to use functions and callbacks in node.js to work through async, but I am not sure how to get a query to equal to a variable. What I am trying to do in this code is take a friend collection that belongs to a user and return the friends result(which I don't think I am doing correctly in the query insertAll) and then find the user's info for each of the query. And then return the results as a render. I am not sure how to call render either with this...
Here is my code:
exports.contactList = function(req, res) {
var insertFriend = function(data, callback) {
var friend = User.findById({_id: user.friendStatus.fuId}, function() {
callback(null, data);
}, friend);
};;
var insertAll = function(coll, callback) {
var queue = coll.slice(0),
friendX;
(function iterate(){
if(queue.length === 0) {
callback();
return;
}
friendX = queue.splice(0,1)[0];
insertFriend(friendX, function(err, friendX) {
if(err) {throw err;}
console.log(friendX + ' inserted');
process.nextTick(iterate);
});
})();
};
insertAll([Friend.findOne({userId: req.signedCookies.userid})], function(){
});
};
A Query object is returned if you do not pass a callback.
From http://mongoosejs.com/docs/queries.html:
When a callback function:
is passed, the operation will be executed immediately with the results passed to the
callback.
is not passed, an instance of Query is returned, which provides a special QueryBuilder
interface for you.