Mongoose Populate in Node JS/express js - node.js

Question

I'm trying to link between two mongoose collections. So that user's information are stored in a collection named user, and his content is stored in another collection.
So far I copied some code from here and edited it;
then with Postman, I created a username named "example";
then I created a post with a random content, and as author I set it "example", but it seems that it doesn't work, when I get '/test' it logs :
Populated User { posts: [], _id: 5c530cd4ede117109cf1a5e9,
username: 'example', __v: 0 }
posts is empty as you see, what should I change in order to fix that?
const UserSchema = new mongoose.Schema({
username: String,
posts: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Post'
}]
})
const PostSchema = new mongoose.Schema({
content: String,
author: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User'
}
})
function getUserWithPosts(username){
return User.findOne({ username: username })
.populate('posts').exec((err, posts) => {
console.log("Populated User " + posts);
})
}
const Post = mongoose.model('Post', PostSchema, 'posts');
const User = mongoose.model('User', UserSchema, 'users');
app.post('/testUser', (req, res) => {
var username = req.body.username;
var clientModel = new User({
username: username,
});
clientModel.save(function (error) {
if (error) {
console.log(error);
}
res.send({
success: true,
username: username,
message: 'account saved successfully!'
});
});
});
app.post('/testPost', (req, res) => {
var content = req.body.content;
var author = req.body.author;
var clientModel = new Post({
content: content,
author: author
});
clientModel.save(function (error) {
if (error) {
console.log(error);
}
res.send({
success: true,
content: content,
author: author,
message: 'account saved successfully!'
});
});
});
app.get('/test', (req, res) => {
res.send({
posts: getUserWithPosts("example")
})
});

Answer 1

EDIT
I see whats going on here now. It appears you have an issue of circular references. Your user.posts references the posts that the user created. The posts.author references the author who created the post. If you want to make this work, you will have to go in and update the user object, after you create the post object, and pass in the post._id.
You can do one other, better thing. You can use virtuals. Mongoose can calculate values run time that reference other collections. This would be my suggestion. The downside is, virtuals are not stored in the database, and you have to explicitly populate this field every time you want it. Heres an example:
User Model
const UserSchema = new mongoose.Schema({
username: String
})
UserSchema.virtual('posts', {
ref: 'Post',
localField: 'username',
foreignField: 'author',
justOne: false
});
This will create the virtual, and whenever you find a user and call .populate('posts'), you will get a array of posts back which the user has authored.
Read more about mongoose virtuals here: http://thecodebarbarian.com/mongoose-virtual-populate