how to find model in ActionCable `subscribed` method - ruby-on-rails

Question

I've seen a lot of tutorials do something like this with the subscribed method:
class MessagesChannel < ApplicationCable::Channel
def subscribed
conversation = Conversation.find(params[:id])
stream_from "conversation_#{conversation.id}"
end
end
The idea being to allow for multiple conversations between multiple users. But I'm not clear on how that id param is sent to the method. If my routes are nested so that the conversation id is in the url, it seems like it should work.
resources :conversations, only: [:index, :create] do
resources :messages, only: [:index, :create]
end
However, the channel code above gives this error:
[ActionCable] [user] Registered connection (Z2lkOi8vZnJhY3Rpb25jbHViL1VzZXIvMQ)
[ActionCable] [user] Could not execute command from ({"command"=>"subscribe", "identifier"=>"{\"channel\":\"MessagesChannel\"}"}) [ActiveRecord::RecordNotFound - Couldn't find Conversation without an ID]: /Users/user/.rvm/gems/ruby-2.5.0/gems/activerecord-5.2.0/lib/active_record/relation/finder_methods.rb:431:in `find_with_ids' | /Users/user/.rvm/gems/ruby-2.5.0/gems/activerecord-5.2.0/lib/active_record/relation/finder_methods.rb:69:in `find' | /Users/user/.rvm/gems/ruby-2.5.0/gems/activerecord-5.2.0/lib/active_record/querying.rb:5:in `find' | /Users/user/.rvm/gems/ruby-2.5.0/gems/activerecord-5.2.0/lib/active_record/core.rb:167:in `find' | /Users/user/code/project/app/channels/messages_channel.rb:3:in `subscribed'
How would I pass the conversation id to the subscribed method so that my users can have multiple private conversations?
Update 1: This is my messages.coffee file
App.messages = App.cable.subscriptions.create
channel: "MessagesChannel"
conversation_id: 1
connected: ->
console.log 'Connected'
disconnected: ->
console.log 'Disconnected'
received: (data) ->
console.log 'Received'
$('#messages').append(data.message)
speak: (message, conversation_id) ->
#perform 'speak', message: message, conversation_id: conversation_id
$(document).on 'turbolinks:load', ->
submit_message()
scroll_bottom()
submit_message = () ->
$('#response').on 'keydown', (event) ->
if event.keyCode is 13
App.messages.speak(event.target.value)
event.target.value = ""
event.preventDefault()
scroll_bottom = () ->
$('#messages').scrollTop($('#messages')[0].scrollHeight)

Answer 1

This is how I am tackling this,
In my view form:
<%= form_for Message.new,remote: true,html: {id: 'new-message',multipart: true} do |f| %>
<%= f.hidden_field :chat_id, value: chat.id,id: 'chat-id' %>
....
Notice the id I have given to form and then chat_id field.
Then in my chat.js:
return App.chat = App.cable.subscriptions.create({
channel: "ChatChannel",
chat_id: $('#new-message').find('#chat-id').val()
}
Now I can use this chat_id param in my ChatChannel like this:
def subscribed
stream_from "chat_#{params['chat_id']}_channel"
end
EDIT:
In your case:
your MessagesChannel subscribed action should be like this:
def subscribed
stream_from "conversation_#{params[:conversation_id]}"
end