Rails Action Cable: How can I access instance variables within ApplicationCable::Channel Class?

Question

I would like to create chatrooms per product page so that uses can chat about the product while they are isolated from other products' discussions.

For this purpose; I was planning to use @product instance varialbe while defining the subscriptions however it seems; instance variables are not accessible within Action Cable

"app/channels/product_channel.rb"

class ProductChannel < ApplicationCable::Channel
  def subscribed
    stream_from "room_channel_product_#{@product.id}"
  end

  def unsubscribed
  end
end

How can I access instance variables within channel module??

Answer 1

I think you can't access the instance variable while defining the subscriptions. But you can pass product_id as a parameter, then you subscribe to the ProductChannel. https://guides.rubyonrails.org/action_cable_overview.html#subscriber

App.cable.subscriptions.create { channel: "ProductChannel", product_id: your_product_id }

And on your channel, you can access to "product_id" like:

def subscribed
  stream_from "product_channel_#{params[:product_id]}"
end