SubsManager

Subscriptions Manager for Meteor

This is a general-purpose subscriptions manager for Meteor. You can use Subscription Manager to cache subscriptions in the client side. This will help you to reduce the CPU usage of your app and improve the client side experience.

Why?

Normally you invoke subscriptions inside the template level or in the router level(in the case of Iron Router). So, when you are switching routes or changing templates/components, subscriptions will run again.

Normally, users go back and forth in your app in a single session. So, in each those route/page changes, app will re-subscribe data from the server. That's a waste and slow down your app in the client side.

Solution

Subscriptions Manager caches your subscriptions in the client side. So, when the user switching between routes, he will no longer have to wait. Also, Meteor won't need to re-send data that's already in the client.

In technical terms, Subscriptions Manager runs it's own Tracker.autorun computation internally. It does not interfere with Router or Templates. It works independently.

Subscriptions Manager does not cache your individual data. It tells Meteor to cache the whole subscription. So, your data will get updated in the background as usual.

Usage

Installation:

meteor add meteorhacks:subs-manager

Then create a new SubsManager instance:

PostSubs = new SubsManager();

Then instead of subscribing to Meteor.subscribe(), use PostSubs.subscribe(). Check this example:

Template.blogPost.onCreated(function() {
    var self = this;
    self.ready = new ReactiveVar();
    self.autorun(function() {
        var postId = FlowRouter.getQueryParam('postId');
        var handle = PostSubs.subscribe('singlePost', postId);
        self.ready.set(handle.ready());
    });
});

Here's how this works:

• Let's say you visit page /posts?postId=abc.
• Then Meteor will subscribe to the singlePost publication with abc as the postId.
• Then let's imagine you visit to /posts?postId=bbc.
• Just like above, it'll subscribe to the singlePost publication with bbc as the postId.
• Now, let's say we go back to /posts?postId=abc. Then, subsManager won't fetch data again from the server. Subscription is already exists inside the client.

Check following links for more information:

• Related docs in the FlowRouter Guide
• BulletProof Meteor Lesson

Resetting

Sometime, we need to re-run our subscriptions due to various reasons.

Eg:- After a user has update the plan.

In those situations, you can try to reset Subscription Manager.

var subs = new SubsManager();

// later in some other place
subs.reset();

Clear Subscriptions

In some cases, we need to clear the all the subscriptions we cache. So, this is how we can do it.

var subs = new SubsManager();

// later in some other place
subs.clear();

Cache Control

Since now you are caching subscriptions, the Meteor server will also cache all your client data. But don't worry - that's not a huge issue.

But, you can control the caching behavior. Here's how to do it.

var subs = new SubsManager({
    // maximum number of cache subscriptions
    cacheLimit: 10,
    // any subscription will be expire after 5 minute, if it's not subscribed again
    expireIn: 5
});

Patterns for using SubsManager

Using a global Subscription Manager

You can create a global subscription manager as shown in the above example. By doing that, all your subscriptions are cached as a whole.

Using separate Subscription Managers

If you need more control over caching, you can create separate Subscription Managers for each set of subscriptions and manage them differently.

If you are using SubsManager inside a ReactComponents, this is the suggested way.

Using global ready checking

You can also check the ready status of all the subscriptions at once like this:

var subs = new SubsManager();
subs.subscribe('postList');
subs.subscribe('singlePost', 'id1');

Tracker.autorun(function() {
  if(subs.ready()) {
    // all the subscriptions are ready to use.
  }
});

Cache subscriptions you only need

With Subscription Manager you don't need to use it everywhere. Simply use it wherever you need without changing other subscriptions.

Limitations

Subscription Manager aims to be a drop-in replacement for Meteor.subscribe (or this.subscribe() in Iron Router). At the moment, the following functionality doesn't work.

• onError and onReady callbacks (issue)