Refer user data in post collection using Mongoose - node.js

Question

I created login & registration page and users data is being stored in user collection. Also did functionality for adding & viewing new post created by loggedin user. So whenever a user is creating the post, I need to refer the user data (username) in post collection. I have checked some forums, but not able to understand populate method. I need to know about referencing data in schema and how to fetch the data from user collection and use it in post collection.
Here is the User Model
var UserSchema = new mongoose.Schema({
username: {
type: String,
index: true
},
password: {
type: String
},
email: {
type: String
},
name: {
type: String
},
profileimage: {
type: String
},
uposts: [{ type: Schema.Types.ObjectId, ref: 'Post'}]
});
var User = module.exports = mongoose.model('User', UserSchema);
Here is the Post Model
var PostSchema = new mongoose.Schema({
_id: mongoose.Schema.Types.ObjectId,
postimage: {
type: String
},
author: {
type: Schema.Types.ObjectId,
ref: "User"
// username: String
},
});
var Post = module.exports = mongoose.model('Post', PostSchema);
Route for adding new post
router.post('/add', upload.single('postimage'), (req, res, next) => {
if(req.file) {
console.log('Uploading File..');
var postimage = req.file.filename;
} else {
console.log('No File Uploaded');
var postimage = 'noimage.jpg';
}
var newPost = new Post({
postimage: postimage
});
Post.createPost(newPost, (err, post) => {
if(err) throw err;
console.log(post);
});
req.flash('success', 'Successfully Created Posts');
res.location('/');
res.redirect('/');
});
Router for displaying Posts
router.get('/view', ensureAuthenticated, (req, res, next) => {
// res.render('viewpost', { user: req.user });
Post.find({_id: {$ne: req.user._id}}, (err, posts) => {
if(err) {
console.log(err);
} else {
res.render('viewpost', {currentUser: req.user, posts: posts});
}
});
});
Also I need to display the post details of other users except the loggedin user.
It would be really helpful, if you could provide a suitable method for the same.

Answer 1

Before Apply please check mongoDB version,
router.get('/view', ensureAuthenticated, async(req, res, next) => {
try {
const posts = await Post.aggregate([
{
$match: { userId: { $ne: req.user._id }}
},
{
$lookup: {
from: "users",
localField: "userId",
foreignField: "_id",
as: "user"
}
},{
$project: {
postimage: "$postimage",
user: { $arrayElemAt: ["$user", 0] }
}
}
])
res.render('viewpost', {currentUser: req.user, posts: posts, error: ''});
} catch(error) {
res.render('viewpost', { currentUser: req.user, posts: [], error: error});
}
})
If no result found please make req.user._id as ObjectId using mongoose.Types.ObjectId(req.user._id)