using ActiveRecord outside rails

ar_example.rb

require 'rubygems'
require 'active_record'
require 'mysql2'
require 'yaml'

dbconfig = YAML::load(File.open('database.yml'))
ActiveRecord::Base.establish_connection(dbconfig)
class Duck < ActiveRecord::Base
end
puts Duck.count

database.yml

adapter: mysql
database: dbfile
username: username
password: 123
host: localhost

note

gem install mysql2
add require 'mysql2' to ar_example.rb

create a table 'ducks' in database 'dbfile'