How to read a collection that depends on another one in Meteor - mongodb

Question

I'm trying to load the latest post from a collection and at the same time all of the comments of that same post. The collection have references instead of storing the whole documents inside each other:
Post { title, body, etc..}
Comment { postId, body, etc.. }
I'm using iron-router as the routing package and in the route of my page I'm subscribing with this way:
this.route('home', {
path: '/',
template: 'home',
waitOn: function () {
return [
Meteor.subscribe('latestPost'),
Meteor.subscribe('lastReadPost')
];
}
});
The code that retrieves the post is simply:
Posts.findOne({}, {sort:{createdAt:-1, limit:1}});
Now the problem is that I don't know how to retrieve the comments without reading the whole collection. I can't subscribe in the router as I still do not have the post ID to query the Comments collection.
I guessed I could do that from the Template, but of course if I query the Comments collection, it's still empty. But I do have the postId as it's inside the Posts collection at that time. But I would need to trigger a subscription from the Template and that doesn't sound like a clean solution.
What would the best practice be? Thanks!

Answer 1

Server side code:
Meteor.publish("latestPost", function () {
var post = Posts.find({}, {sort:{created:-1}}).fetch()[0];
console.log("publish : " + post.title);
return [
Posts.find({_id: post._id}),
Comments.find({postId: post._id})
];
});
Client side code:
this.route('home', {
path: '/',
template: 'home',
waitOn: function () {
return [
Meteor.subscribe('latestPost')
];
},
data:function(){
return {
post:Posts.findOne(),
comments:Comments.find()
};
}
});
Check this repository to see whole example.
After user changes to another route, then subcriptions are being automatically stopped.

Answer 2

I would also include a limit in the server side finder options
{sort : {created : -1}, limit : 1}