Question

I’m creating a model called Chats. And I want to assign users to a discussion. They are either a part of the Chats or they aren’t…

So I create one model Chats.

What’s the standard Rails naming convention for the other table?

ChatUsers?

Answer 1

While has_and_belongs_to_many is an ok option here, I recommend going with has_many :through instead.

In essence you will have an explicit join model, which you can call something like ChatSession.

class Chat < ActiveRecord::Base
  has_many :chat_sessions
  has_many :users, :through => :chat_sessions
end

class User < ActiveRecord::Base
  has_many :chat_sessions
  has_many :chats, :through => :chat_sessions
end

class ChatSession < ActiveRecord::Base
  belongs_to :user
  belongs_to :chat
end

Now you will need a table called chat_sessions with columns :user_id, and :chat_id in it. This is your join table.

Advantage

You get a model which is fully under your control, and isn’t just a dumb join table managed by rails. So for example, if you want to track number of messages particular user left in particular chat, it could be a column in chat_sessions table. Presence of :through renders habtm unneeded in most cases. There is no complexity overhead either.