Class-based subscription fields

[rmosolgo]

The current subscription system leaves a lot to be desired, see for example #1528 #1799 #1910

I'm proposing a GraphQL::Schema::Subscription like GraphQL::Schema::Mutation with authorization, initialization, and update methods.

You can see the rendered doc here: https://github.com/rmosolgo/graphql-ruby/blob/good-subscriptions/guides/subscriptions/subscription_classes.md

TODO:

• What if you don't want to update a certain client of an event? (For example, that client triggered the event)

[theorygeek]

Nice! I like it. How do you hook up the transport? I'm assuming there needs to be some method that GraphQL can invoke when an update needs to be sent to a client?

Then, def update will be called for each client's subscription

It is going to send the update to every client by default, and your update should return skip if that particular client doesn't need the update?

[rmosolgo]

Thanks for taking a look!

How do you hook up the transport?

That consideration is separated a bit. The changes here revolve around how subscriptions are evaluated by GraphQL, but not how the result is transmitted to clients.

In terms of transport, the subscription implementation should define #deliver for sending payloads to clients. See ActionCable's #deliver for example.

every client by default?

Yes, that's right. I'm glad you mentioned it: it should really have a way to halt, and send nothing to a client if desired, but there's not a way to do that yet. I added a TODO above.

[modosc]

What if you don't want to update a certain client of an event?

we've hit this a few different times - mostly because of my understanding on how scoping works it's hard to have multidimensional filters (ie, company A + role B). we sometimes end up sending out notifications on a model which is not visible for some clients. if we allow the subscription field to be null, then we send out empty messages to a bunch of clients. my hacky solution was to make the field non-nullable and hide the Cannot return null for non-nullable field Subscription.foo error but this isn't great. ideally there'd be some option for "not null for the client but if the server returns null just skip delivery".

[rmosolgo]

It's basically implemented as written, feel free to take another look if you're interested! Otherwise I'll merge it tomorrow or so.

[phyllisstein]

I'm so excited about this @rmosolgo, thank you for all your amazing work. ✨