Incomprehension about the first example in Rails' Guide for action cable

Question

I am trying to add the User Appearances example (from the Rails' Guide : https://guides.rubyonrails.org/action_cable_overview.html#example-1-user-appearances ) in my app but I don't understand this part :

# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
  def subscribed
    current_user.appear
  end

  def unsubscribed
    current_user.disappear
  end

  def appear(data)
    current_user.appear(on: data['appearing_on'])
  end

  def away
    current_user.away
  end
end

If someone has an explanation for the following sentence : "That appear/disappear API could be backed by Redis, a database, or whatever else." (Just above this part of code in the Rails' Guide).

I try several options, as adding a method "appear" in my model User which change on "true" a database value from my model User, but the subscribed definition call current_user.appear and then the appear definition call current_user.appear(with_param) generates a conflict ...

There is probably something I don't understand but I don't see exactly what is it ...

Thank you very much for your answers.

Answer 1

The sentence about "appear/disappear API backing" - means that ActionCable does not care where and how you are storing and handling users statuses - you may store only a flag or more data in database (like last seen chatroom, last seen time etc.), you may store similar data in redis or any other place you like.

(un)subscribed methods are caller by ActionCable itself upon user (dis)connection to that channel(usually this happens on page load and after navigating away/closing - and while page is open in browser it does not necessary mean that user is actually near their device), while appear/away are actions that are called from clientside js via calling perform("action_name_here") on the channel. Example assumes that clientside code will detect user presence and send updates.