Node.js loop over array of objects asynchronously

Question

Sorry if the title itself is a contradiction :) JS beginner here..

I get an array of MongoDB documents and I want to extend each one with another object (from another table) so that I can pass this array of extended objects to my view. I want to achieve something like this:

exports.myFunction = function(req, res) {
    Book.find({'good': true}).exec(function(err, docs) { // find good books
        // add authors to each book (?):
        for (var i = 0, i < docs.length; i++) {
            docs[i].author = Author.findOne({'_id': docs[i].author_id}); 
        }
        // render books:
        res.render('/books.ejs', {books: docs});
    });
}

I think this is not the JavaScript-way to do it :) So how can I achieve this?

Thanks,

chridam · Accepted Answer · 2017-01-02 03:24:45Z

2

Use the $lookup function as found in the aggregation framework. The following example demonstrates how you can apply that in your case:

exports.myFunction = function(req, res) {
    Book.aggregate([
        { "$match": { "good": true } },
        {
            "$lookup": {
                "from": "authors"
                "localField": "author_id",
                "foreignField": "_id",
                "as": "author"
            }
        },
        { "$unwind": "author" }
    ]).exec(function(err, docs) { 
        res.render('/books.ejs', {books: docs});
    });
}

answered Jan 2, 2017 at 3:24

chridam

104k26 gold badges246 silver badges243 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jeff · Accepted Answer · 2017-01-02 12:31:01Z

1

I found another solution, which is using populate.

For this, I needed to change my Book model,

from:

var mongoose = require('mongoose');

var bookSchema = mongoose.Schema({
author_id: String,
good: Boolean
});

to:

var mongoose = require('mongoose');
var Author = require('./author.js'); // added this

var bookSchema = mongoose.Schema({
author: { type: mongoose.Schema.Types.ObjectId, ref: 'Author' },
good: Boolean
});

And I chain populate() to my initial query as follows:

exports.myFunction = function(req, res) {
    Book.find({'good': true}).populate('author').exec(function(err, docs) { // find good books
        // render books:
        res.render('/books.ejs', {books: docs});
    });
}

edited Jan 2, 2017 at 12:31

answered Jan 2, 2017 at 3:33

jeff

13.8k32 gold badges86 silver badges138 bronze badges

Collectives™ on Stack Overflow

Node.js loop over array of objects asynchronously

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related