gistfile1.rb

require 'data_mapper'

class Post
  include DataMapper::Resource

  property :id, Serial

  before :save, :categorize
  before :update, :categorize
  before :create, :categorize

  def categorize
    puts "W T F"
    throw :halt
  end
end

DataMapper.setup(:default, "sqlite::memory:")
DataMapper::Logger.new($stdout, :debug)
DataMapper.finalize.auto_migrate!

Post.create!
Post.create!
Post.create!
Post.create!
Post.create!

puts "#{Post.all.map {|a| a.id}.join(' ')}  done"