Use concerns to keep your models manageable

gistfile1.rb

# autoload concerns
module YourApp
  class Application < Rails::Application
    config.autoload_paths += %W(
      #{config.root}/app/controllers/concerns
      #{config.root}/app/models/concerns
    )
  end
end

# app/models/concerns/trashable.rb
module Trashable

 def self.include(model_klass)
    model_klass.class_eval do
      extend ClassMethods
      include InstanceMethods
      default_scope   where(trashed: false)
      scope :trashed, where(trashed: true)
    end
 end

 module ClassMethods
   def something_at_class_level; end
 end

 module InstanceMethods
   def trash
     update_attribute :trashed, true
   end
 end

end

# app/models/message.rb
class Message < ActiveRecord::Base
  include Trashable, Subscribable, Commentable, Eventable
end