## document.rb

class Document
  include DataMapper::Resource
  property :id, Integer, :serial => true
  property :name, String, :nullable => false, :lazy => false
  property :body, Text

  property :created_at, DateTime
  property :updated_at, DateTime

  belongs_to :group
  has n, :attachments, :through => Resource
  is_versioned :on => :updated_at
end

## attachment.rb

class Attachment
  include DataMapper::Resource
  include Paperclip::Resource

  property :id, Integer, :serial => true
  property :comments, String, :length => 255

  has_attached_file :attachment

  has n, :documents, :through => Resource
end