How to obtain object id and also how to update - node.js

Question

I am trying to obtain the object id for any article already in db so that I can validate that the article exists before comments are made.
The issue is on the router (/blog/article/comment). I cannot get the article object id from /blog/article/:postid. I want to pass this id to articleId like this:
articleId: req.params.postid
I have also tried:
articleId: req.article._id
model structure: comment.js
var mongoose = require('mongoose');
var CommentSchema = new mongoose.Schema({
content: { type: String },
user: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
articleId: { type: mongoose.Schema.Types.ObjectId, ref:'Article' },
dateCommented: { type: Date, default : Date.now }
});
Article model: article.js
var ArticleSchema = new mongoose.Schema({
category: { type: mongoose.Schema.Types.ObjectId, ref: 'Category' },
commentId:{type: mongoose.Schema.Types.ObjectId, ref:'Comment'},
title: String,
author: { type: mongoose.Schema.Types.ObjectId, ref: 'User'},
blog: [{
topic: { type: String, unique: false, lowercase: true },
body: { type: String, unique: false, lowercase: true },
tags: [ 'first', 'mongodb', 'express'],
created: Date,
modified: { type : Date, default : Date.now },
state: { type: String, unique: false, lowercase: true }
}]
});
main.js
router.param('postid', function(req, res, next, id) {
if (id.length !=24) return next(new Error ('The post id is not having the correct length'));
//articleId: req.param('postid'),
Article.findOne({ _id: ObjectId(id)}, function(err, article) {
if (err) return next(new Error('Make sure you provided correct post id'));
req.article = article;
next();
});
});
router.get('/blog/article/:postid', function (req, res, next) {
Article.findById({ _id: req.params.postid }, function (err, article) {
if (err) return next(err);
res.render('main/publishedArticle', {
article: article
});
});
});
router.post('/blog/article/comment', function(req, res, next) {
async.waterfall([
function(callback) {
var comment = new Comment({
articleId: req.params.postid,
content: req.body.content,
user: req.user._id
});
comment.save(function(err) {
if (err) return next (err);
req.flash('success', 'Thank you for your comment');
callback(err, comment);
});
},
function(comment) {
Article.update({_id : comment.articleId }, { $set: { commentId: {} }}, function(err, updated) {
if (updated) {
res.redirect('/')
}
});
}
]);
});
Another issue I have is how to update the commentId for each comment in the Article
Article.update({_id : comment.articleId }, { $set: { commentId: {} }}, function(err, updated)

Answer 1

Since the /blog/article/comment route is a post request. Just submit your articleId in the body of that request. You'll have to send it up from the client. You can access it with req.body.articleID (If that is what you call the variable).
See here for more info on POST requests in node.
For your second question:
Within your article schema you have commentId, That is a single record. What you want is an array of comments. Something like this:
comments: [{type: mongoose.Schema.Types.ObjectId, ref:'Comment'}]
Then within your code...
...
function(comment) {
//comment should contain all the comments
//Grab the article
Article.findOne({ _id: comment.articleId}, function(err, article){
//Go through all the comments in 'comment' compare them with the ones in artcle.comments.
//The ones that aren't already in the article object get put into newComments...
var newComments = [];
Article.update({ _id: comment.articleId }, { $addToSet: { comments: newComments } }, function(err, updated) {
if (updated) {
res.redirect('/')
}
});
});
}
...
I didn't fully implement the code, but it should get you off to the right start.
addToSet Documentation
Some more examples of add to set