Meteor Iron-Router: Wait for Subscription sequential - meteor

Question

I have the following route defined in my iron-router:
this.route("/example/:id", {
name: "example",
template: "example",
action: function () {
this.wait(Meteor.subscribe('sub1', this.params.id));
this.wait(Meteor.subscribe('sub2', <<data of sub1 needed here>>));
if (this.ready()) {
this.render();
} else {
this.render('Loading');
}
}
});
I want to wait for sub1 and sub2 before rendering my actual template. The problem is that I need a piece of data which is part of the result of sub1 for the sub2 subscription.
How can I wait sequential for subscriptions? So that I can split the wait in two steps and wait for my first subscription to be finished. Then start the second subscription and then set this.ready() to render the template?
A workaround that I thought of was to use Reactive-Vars for the subscriptions and dont use .wait and .ready which is provided by iron-router. But I would like to use a more convenient solution provided by iron-router or Meteor itself. Do you know a better solution for this?
Thanks for your answers!

Answer 1

Publish Composite Package:
If the second subscription is reactively dependent on certain fields from the first dataset -- and if there will be a many-to-many "join" association, it might be worth looking into reywood:publish-composite package:
It provides a clean and easy way to manage associated subscriptions for collections with hierarchical relations.
Publication:
Meteor.publishComposite('compositeSub', function(id) {
return {
find: function() {
// return all documents from FirstCollection filtered by 'this.params.id' passed to subscription
return FirstCollection.find({ _id: id });
},
children: [
find: function(item) {
// return data from second collection filtered by using reference of each item's _id from results of first subscription
// you can also use any other field from 'item' as reference here, as per your database relations
return SecondCollection.find({ itemId: item._id });
}
]
}
});
Subscription:
Then you can just subscribe in the router using:
Meteor.subscribe('compositeSub', this.params.id);
Router hooks:
As a suggestion, hooks in iron-router are really useful, as they take care of a lot of things for you. So why not use the waitOn hook that manages this.wait and loading states neatly?
this.route('/example/:id', {
name: "example",
template: "example",
// this template will be rendered until the subscriptions are ready
loadingTemplate: 'loading',
waitOn: function () {
// return one handle, a function, or an array
return Meteor.subscribe('compositeSub', this.params.id);
// FYI, this can also return an array of subscriptions
},
action: function () {
this.render();
}
});
You can use the configure option to add a template for loading event:
Router.configure({
layoutTemplate: 'layout',
loadingTemplate: 'loading'
});
Note regarding the comment in question:
If both subscriptions only depend on the same id parameter passed to it, you can use the following, as mentioned by #abj27 in the comment above -- however, this does not seem to be the case, going by your example:
Publication:
Meteor.publish("subOneAndTwo", function (exampleId) {
check(exampleId, String);
return [
FirstCollection.find({ _id: exampleId });
SecondCollection.find({ firstId: exampleId })
];
});
Subscription:
Meteor.subscribe('subOneAndTwo', this.params.id);
So just check what you need and use a solution accordingly.

Answer 2

https://github.com/kadirahq/subs-manager
With this package, you can assign a subscription to a variable. Then, you can check that variable's ready state. I just got this working... after years of trying to understand.
Here is my code snippet that works, but oddly I had to wrap it in a 1ms timeout to work...
```
Router.route('/activity/:activityId', function (params) {
var params = this.params;
setTimeout(function(){
var thePage = window.location.href.split("/");;
window.thePage = thePage[4];
dbSubscriptionActivites.clear();
window.thisDbSubscriptionActivites = "";
window.thisDbSubscriptionActivites = dbSubscriptionActivites.subscribe("activityByPage", window.thePage);
Tracker.autorun(function() {
if(window.thisDbSubscriptionActivites.ready()) {
dbSubscriptionComments.clear();
window.thisDbSubscriptionComments = "";
window.thisDbSubscriptionComments = dbSubscriptionComments.subscribe('fetchComments', "activity", Activities.findOne({})._id);
BlazeLayout.render("activity");
$('body').removeClass("shards-app-promo-page--1");
}
});
},1); // Must wait for DOM?
});
```
Examine: window.thisDbSubscriptionActivites = dbSubscriptionActivites.subscribe("activityByPage", window.thePage);
I'm setting as a window variable, but you could do a const mySub = ...
Then, you check that in the autorun function later.
You can see there is where I am doing subscriptions.
I suppose I really should move the BlazeLayout render in to another .ready() check for the comments.