Displaying content from different mongoose tables on one view - node.js

Question

I'm a (relatively inexperienced) Java EE developer who is looking to learn node.js. I'm working with the express framework, mongodb, and the mongoose framework. I've been working on building a simple blog site (just for practice) with an mvc like architecture. It would have would have 4 mongodb collections: post, image, user, comment. The basic Schemas are as follows:
postSchema = mongoose.Schema({
id: Number,
dateCreated, {type: Date, default: Date.now}
title: String,
content: String
});
var Post = mongoose.model('Post', postSchema);
imageSchema = mongoose.Schema({
id: Number,
postId: Number,
path: String
});
var Image = mongoose.model('Image', imageSchema);
userSchema = mongoose.Schema({
id: Number,
username: String,
password: String,
email: String
});
var User = mongoose.model('User', userSchema);
commentSchema = mongoose.Schema({
id: Number,
postId: Number,
userId: Number,
dateCreated: {type: Date, default: Date.now},
content: String
});
var Comment = mongoose.model('Comment', commentSchema);
I want to be able to show a post, an image, comments, and user info all on one page. My issue is that I can't quite figure out how retrieve and send all this data in an asynchronous way. This seems to be what most of the examples I have found do (not necessarily all in one file):
app.get('/', function(res, req) {
Post.findOne(function(err, post) {
if (err) return res.send(500);
res.render('index', post);
});
});
This wouldn't work for me because I would info from the image, comment, and user collections as well. Is there an asynchronous way to do this? If not is there a way to reconfigure what I have so that it could be asynchronous? (I'm trying to get a feel for asynchronous programming.)
Thanks in advance!

Answer 1

Simples way to do this as-is would be to use promises and perform simultaneous async operations:
Post.findOne(id).then(post => {
let postId = post.id;
return Promise.all([
Comments.find({postId}),
Images.find({postId}),
// Not sure what query you need here
User.find(),
post,
]);
}).then(data => {
let [comments, images, users, post] = data;
res.render('index', {comments, images, users, post});
});
In your index template you would have an object with the four properties.
You can perform simultaneous async operations without promises, but I'll leave that for someone else to talk about. I would prefer to work with promises.
Mongoose will also allow you to use other schema definitions as data types as in:
commentSchema = mongoose.Schema({
id: Number,
postId: Post,
userId: User,
dateCreated: {type: Date, default: Date.now},
content: String
});
In this case you can use .populate after some queries in order to perform another query under the hood -- e.g. get the post data for a comment.
Since you are using MongoDB -- a NoSQL Database -- I would look into denormalizing the data and keeping it flat. Firebase, which stores data in a similar structure has a great article on how to store and use denormalized data