Railsで別データベースでテーブルを扱う

モデル

class Country < ActiveRecord::Base
  attr_accessible :name
  def self.table_name_prefix
    'messages_development.'  
  end
  establish_connection "development"
  has_many :prefectures
  scope :testname ,joins(:prefectures)
end

class Prefecture < ActiveRecord::Base
  attr_accessible :name
  def self.table_name_prefix
    'messages_staging.'  
  end
  establish_connection "staging"
  belongs_to :country
end

database.yml

development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: messages_development
  pool: 5
  username: root
  password:
  socket: /tmp/mysql.sock

staging:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: messages_staging
  pool: 5
  username: root
  password:
  socket: /tmp/mysql.sock

ja = Country.create(name: "Japan")

INSERT INTO `messages_development`.`countries` 
(`created_at`, `name`, `updated_at`) 
VALUES 
('2012-05-30 08:28:02', 'Japan', '2012-05-30 08:28:02')

pre = Prefecture.create(name: "Tokyo")

INSERT INTO `messages_staging`.`prefectures` 
(`country_id`, `created_at`, `name`, `updated_at`) 
VALUES 
(NULL, '2012-05-30 08:30:17', 'Tokyo', '2012-05-30 08:30:17')

ja.prefectures << pre

UPDATE `messages_staging`.`prefectures` 
SET `country_id` = 2, 
`updated_at` = '2012-05-30 08:31:59' 
WHERE `messages_staging`.`prefectures`.`id` = 2

SELECT `messages_staging`.`prefectures`.* 
FROM `messages_staging`.`prefectures` 
WHERE `messages_staging`.`prefectures`.`country_id` = 2

Country.testname

SELECT 
  `messages_development`.`countries`.* 
FROM `messages_development`.`countries` 
INNER JOIN `messages_staging`.`prefectures` 
ON `messages_staging`.`prefectures`.`country_id` = `messages_development`.`countries`.`id