Lot’s of questions are popping up about subscription management and I wanted to start listing some of the references and questions. Maybe generate a FAQ or something. Not sure this is the right place to do it but here it goes nonetheless:
- This post about a template subscription pattern seems to have at least partially inspired the recently release of more built-in template subscriptions
- this response by @serkandurusoy and this blog post related @arunoda flow-router starts to talk about when and where template subscription make sense vs. router based subscriptions.
- The above also hint at subscription caching strategies using something like subs-manager or subs-cache by @ccorcos
- I believe running a subscription will start a blocking DDP transaction unless you use something like unblock
- This post by @dandv about understanding publications and subscriptions
- Mergbox - how meteor tracks what portion of a collection has been sent to the client already, and what it sends when a new subscription ask for different but overlapping data
- Subscribing to more data means the user is less likely to wait for loading while using the app but also means longer initial loading. Is it possible to do non-blocking subscriptions on data super-sets (e.g. all blog posts), and do blocking subscriptions for immediately required data (e.g. this blog post I am currently wanting to read)?
- Created a meteorpad to show this does work fine http://meteorpad.com/pad/powp2CTWGAoyfb8va/Subscribe%20Unblock%20Test
- Still an open question of how mergbox works in this scenario (e.g. where in theory adding data to mergbox and transfering data via DDP is interrupted to yield)
- what happens if you do an unblocked subscription, followed immediately by the same subscription but blocked?
- if you subscribe to publisher that returns a full collection, and then subscribe to a second publisher that returns a subset of that collection, is the server smart enough to know the superset has been sent to the client and immediately return ready?
- Mergebox ensures no duplicate data is sent
- this is only true for top level data in a collection (not nested data)
- if you do identical subscriptions but in different contexts (e.g. one at the router level with Meteor.subscribe and one at the template level with this.subscribe) what happens?
- Mergebox ensures no duplicate data is sent
- Not sure about ready handlers??
- if you do two subscriptions to the same publisher but pass a different value (e.g. Meteor.subscribe(“blogposts” blogPostId1) and Meteor.subscribe(“blogPosts” BlogpostId2) what happens?
- Flow-router’s register subscription functionality provides the functionality to check subscription readiness via FlowRouter.subsReady() within an autorun. How would you replicate this without the use of flow-router?
- see response from ccorcos below
- what are some guidelines and things to watch out for when using a subscription manager?
- from @elie can either or both of these subscriptions managers be used in template subscriptions? how?
- borrowed from @mattkrick if two pages currently use the same subscription, this new template-level pattern means I would sub onCreated, stop onDestroyed, then sub again on the new page’s onCreated. This makes me wonder, would it be more efficient to just continue using a Meteor.subscribe if a subscription is used across multiple templates?
- see response from ccros below
- TL;DR depends on flush cycle - add more information about what determines a flush cycle and how to determine if adjecnt subscribes fall within the same cycle
- if you do a this.subscribe() in an onCreated and it returns ready, and then later a new document is added to the collection returned by that subscription how does the “readiness” of that subscription change? Does it always return ready? is ready re-sent when the publish data changes? if so how can you catch that?
- how do you handle subscribing in templates when the template depends on the data from multiple subscriptions and at least one of the subscriptions requires a parameter that can only be extracted from the data returned by one of the other subscriptions … for example you might want user-data of the last user to edit a post, but you can’t do this.subscribe(“post_revisions”) and this.subscribe(“ownerData”, user_ID_embedded_in_the_post_revisions) in onCreated because you only get the user’s ID once the post_revisions subscribe is ready
- this is probably best solved with a new subscribing to a new publish. In the publish you would do a find on the revisions collection, then use the Id to do a find on the users collection, then return both cursors from the publication. Subscribing to this publish will get you all the data you need for this template.
I’m sure a bunch of these are stupid questions or have readily available answers so apologies for that.