## mark a section (Learn more)

class Attachment < ActiveRecord::Base belongs_to :attachable, :polymorphic => :true validates_presence_of :width, :height, :if => Proc.new { |attachment| ["Photo", "Logo"].include? attachment.attachable_type } end class Asset < ActiveRecord::Base has_one :attachment, :as => :attachable end class Photo < Asset end class Logo < Asset end class Video < Asset end

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