MongoDB & Mongoose: unable to populate a user's posts with .populate() - mongodb

Question

I've searched this site for days looking through the many different but similar questions on this topic to no avail.
Here's what I'd like to happen. A user signs in and their posts are automatically linked to the users collection. Eventually I'd like to link posts to the profile it was posted to, but i"m not quite there yet. Here's what I've tried so far.
In the User Schema:
const UserSchema = new Schema({
posts: [{
type: Schema.Types.ObjectId,
ref: 'posts'
}],
firstName: {
type: String,
required: true
},
lastName: {
type: String,
required: true
},
...
});
module.exports = User = mongoose.model('users', UserSchema);
In the Post Schema:
const PostSchema = new Schema({
user: {
type: Schema.Types.ObjectId,
ref: 'users'
},
text: {
type: String,
required: true
},
name: {
type: String
},
...
});
module.exports = Post = mongoose.model('posts', PostSchema);
In my users api, here's how I'm signing the user in and attempting to populate the user's posts:
const User = require('../../models/User');
router.post('/login', (req, res) => {
const { errors, isValid } = validateLoginInput(req.body);
// Check Validation
if (! isValid) {
return res.status(400).json(errors);
}
const email = req.body.email;
const password = req.body.password;
// Find user by email
User.findOne({ email })
.populate('posts')
.then(user => {
if (! user) {
errors.email = 'User not found';
return res.status(400).json(errors);
}
// Check password
bcrypt.compare(password, user.password).then(isMatch => {
if (isMatch) {
// User Matched
// Create JWT Payload
const payload = {
id: user.id,
firstName: user.firstName,
lastName: user.lastName,
name: user.firstName + ' ' + user.lastName,
avatar: user.avatar,
posts: user.posts
};
jwt.sign(
payload,
keys.secretOrKey,
{ expiresIn: 3600 }, (err, token) => {
res.json({
success: true,
token: 'Bearer ' + token,
payload
});
});
} else {
errors.password = 'Password is incorrect';
return res.status(400).json(errors);
}
});
});
});
In the posts api, here's how the post is being submitted:
router.post('/', passport.authenticate('jwt', { session: false }), (req, res) => {
const { errors, isValid } = validatePostInput(req.body);
if (! isValid) {
// Return errors with 400 status
return res.status(400).json(errors)
}
const newPost = new Post({
text: req.body.text,
name: req.body.name,
avatar: req.body.avatar,
user: req.user.id
});
newPost.save().then(post => res.json(post));
});
Currently, all I'm seeing is an empty array and no errors. I've been spinning my wheels on this one for a couple days now so any help would be appreciated. Thanks!

Answer 1

I think you forgot to save the _id of your new post to the User model so that the populate() can lookup the posts to populate:
newPost.save().then(post => {
User.update({ _id: req.user.id }, { $push: { posts: post._id }}, (err) => {
res.json(post));
});
});