Rails: mysql active record

database.yml

adapter: mysql2
username: username
password: password
database: database_name

main.rb

#!/usr/bin/env ruby

require 'rubygems'

gem 'activerecord'

require 'mysql2'
require 'active_record'
require 'logger'
require 'yaml'
require 'set'

dbconfig = YAML::load(File.open('database.yml'))

ActiveRecord::Base.establish_connection(dbconfig)
ActiveRecord::Base.pluralize_table_names = false
# ActiveRecord::Base.logger = Logger.new(STDOUT)


result = ActiveRecord::Base.connection.execute("SELECT * FROM schema_version ORDER BY updated_at DESC LIMIT 1")


class AdUnit < ActiveRecord::Base
end

ActiveRecord::Base.transaction