Loop data with Node.js

Question

I am having my code as

function updateData(data){
    data.forEach(function(obj){
        users.find({_id:obj.userId}).toArray(
        function(e, res) {
            obj.userData = res;
            console.log(res)
        }); 
    });
    return data;
}

The problem is I am unable to find the updated data, I am trying to update my data and adding one more field to it based on userId. The data parameter is an array containing the output from comments table. hope you understand the scenario.

My Head Hurts · Accepted Answer · 2015-02-27 12:24:43Z

1

It looks that users.find({...}).toArray(function(...){...}) is going to be asynchronous, so there is no way that you can be sure that the db call has been completed and that each data.obj has been updated before data is returned.

Instead of using the javascript Array.prototype.forEach() function, you could use the NodeJS async.each function from the async library by Caolan which would iterate through the array, update each object and then return the data object only when all functions calls have completed.

For example:

var async = require("async");

function updateData(data){
    async.each(data, function(obj, callback) {
        users.find({_id:obj.userId}).toArray(
            function(e, res) {
                obj.userData = res;
                callback(e);
            }
        );  
    }, 
    function(error){
        return data;
    }
}

edited Feb 27, 2015 at 12:24

answered Feb 27, 2015 at 10:25

My Head Hurts

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2 Comments

Eshant Sahu Over a year ago

Still getting the same result. I am new with Node.js callback pattern. can you please provide some reference where I can I find more stuff to understand this whole pattern??

My Head Hurts Over a year ago

There is a section called "What are callbacks?" in this tutorial. If you are feeling adventurous then there is this article about "Callback Hell" and how to avoid it. Do your console log messages show up in your terminal? You should also check e to see if an error is being returned

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