How to separate cc and bcc in messages?

chat.rb

class Chat < ActiveRecord::Base
  has_many :user_chats, conditions: { bbc: false }
  has_many :bbc_user_chats, class_name: 'UserChat', conditions: { bbc: true }

  has_many :users, through: :user_chats
  has_many :bbc_users, through: :bbc_user_chats, source: :user
end

user.rb

class User < ActiveRecord::Base
  has_many :user_chats
  has_many :chats, through: :user_chats
end

user_chat.rb

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