Mongoose - trying to do 'JOINS' in MEAN stack - node.js

Question

I am having a hard time understanding the async nature of NodeJS.
So, I have an articles object with this schema:
var ArticleSchema = new Schema({
created: {
type: Date,
default: Date.now
},
title: {
type: String,
default: '',
trim: true,
required: 'Title cannot be blank'
},
content: {
type: String,
default: '',
trim: true
},
creator: {
type: Schema.ObjectId,
ref: 'User'
}
});
and the User schema is:
var UserSchema = new Schema({
firstName: String,
lastName: String,
...
});
The problem is when I query for all the documents like so:
exports.list = function(req, res) {
// Use the model 'find' method to get a list of articles
Article.find().sort('-created').populate('creator', 'firstName lastName fullName').exec(function(err, articles) {
if (err) {
// If an error occurs send the error message
return res.status(400).send({
message: getErrorMessage(err)
});
} else {
// Send a JSON representation of the article
res.json(articles);
}
});
};
I get all the articles back successfully, but for some reasons, the article creator is returning different results
for locally authenticated users (localStrategy) and facebook authenticated users (facebook strategy) for locally authenticated users, I get:
articles = {
creator: {
id: 123,
firstName: 'Jason',
lastName: 'Dinh'
},
...
}
for fb authenticated users, I get:
articles = {
creator: {
id: 123
},
...
}
I can't seem to get a grip on PassportJS API, so what I want to do is
iterate through articles and for each article, find the user document using the article creator ID and add the user firstName and lastName to the articles object:
for each article in articles {
User.findOne({ '_id': articles[i].creator._id }, function(err, person){
//add user firstName and lastName to article
});
}
res.json(articles);
You can probably already see the problem here... my loop finishes before the documents are returned.
Now, I know that MongoDB doesn't have any 'joins' and what I want to do is essentially return a query that 'joins' two collections. I think I'm running into problems because I don't fundamentally understand the async nature of
node.
Any help?

Answer 1

You can use find instead of findOne and iterate inside your callback function.
User.find({ }, function(err, personList){
for each person in personList {
for each article in articles {
if (person._id === article.creator._id) {
//add user firstName and lastName to article
}
}
}
res.json(articles);
});
UPDATE:
Considering the scenario that #roco-ctz proposed (10M users), you could set a count variable and wait for it to be equal to articles.length:
var count = 0;
for each article in articles {
User.findOne({ '_id': articles[i].creator._id }, function(err, person){
//add user firstName and lastName to article
count += 1;
});
}
while (count < articles.length) {
continue;
}
res.json(articles);