app/models/activity.rb
class Activity < ActiveRecord::Base
belongs_to :creator, class_name: 'User'
belongs_to :actor, class_name: 'User'
belongs_to :trackable, polymorphic: true
default_scope -> { order(id: :desc).includes(:actor, :creator, :trackable) }
def actioned
"#{action}ed".gsub(/ed?ed$/, 'ed')
end
end