gistfile1.rb

class Attachment < ActiveRecord::Base
  belongs_to :attachable, :polymorphic => true
  has_attachment :storage => :file_system, 
                 :file_system_path => "public/files/attachments", 
                 :max_size => 100.megabytes
  validates_as_attachment
  
  #
  # Override acts_as_attachment method for inherited classes. Just redefine attachment options instead.
  #
  class << self
    alias_method :old_has_attachment, :has_attachment
    
    def has_attachment(options)
      self.attachment_options.merge!(options)
    end
  end
  
  def thumb(thumbname = :thumb)
    thumbnails.find(:first, :conditions => ['thumbnail=?', thumbname.to_s])
  end  
end