migrate.yml

# Originally posted on http://pastie.org/25291 (1 December 2006)

# Transmigration between two different database configurations.
# Schema must be already in place. e.g: rake db:schema:load
# Licensed in the Public domain (or the DWTFYW License, at your
# option).

# -vjt@openssl.it

source: 
  adapter: mysql
  host: antani.local 
  username: example
  password: antani

dest:
  adapter: postgresql
  host: tapioca.local
  username: example
  password: tapioca

starfish-transmigrate.rb

# -*- ruby, starfish -*-
# 
# starfish: http://www.rufy.com/starfish/doc
# 
# Single table only, this is not intended to copy the whole
# database. enhancements are welcome.
# The table to migrate must be passed via user environment.
#  
# $ MIGRATE_TABLE=service_days starfish lib/starfish-transmigrate.rb &
# [1] 12748
# server started for .........
# 
# once started the server, and a single client process, you can
# then launch as many subsequent client processes as you like.
# 
# $ MIGRATE_TABLE=service_days starfish lib/starfish-transmigrate.rb &
# [2] 43783
# $ MIGRATE_TABLE=service_days starfish lib/starfish-transmigrate.rb &
# [3] 19234
# $ MIGRATE_TABLE=service_days starfish lib/starfish-transmigrate.rb &
# [4] 48923
# 
# - vjt@openssl.it

require 'transmigrate'
raise "#{ARGV[0]}: table name missing!" unless table = ENV['MIGRATE_TABLE']
$klasses = Transmigrate.migration_classes table

server do |map_reduce|
  map_reduce.type = $klasses[0]
  map_reduce.limit = 5000
end

client do |source|
  # yes, I know that this is not DRY. :)
  # 
  o = $klasses[1].new(source.attributes)
  o.id = source.id
  o.save
end

transmigrate.rb

## -*- ruby -*-
## Usage: 
#
# $ script/console
# Loading development environment
# >> require 'transmigrate'
# true
# >> Transmigrate.classes.each &Transmigrate.proc
# processing ProductsSource -> ProductsDest
# [ ... ]
# 
# - vjt@openssl.it

$conf = YAML::load File.open("config/migrate.yml")
class Transmigrate
  class << self
    def classes
      ActiveRecord::Base.connection.tables.map do |table|
        migration_classes table
      end
    end

    def migration_classes(t)
      %w|source dest|.map { |c|
        klass = (t + '_' + c).camelize
        eval %{
          class ::#{klass} < ActiveRecord::Base
            establish_connection $conf['#{c}']
            set_table_name '#{t}'
          end
        }
        klass.constantize
      }
    end

    STEP = 500
    def proc
      Proc.new { |source, dest|
        puts "processing #{source} -> #{dest}"
        dest.silence {
          dest.transaction {
            source.connection.execute("SET character_set_results = 'utf8'");
            (0..source.count).step(STEP) { |offset|
              source.find(:all, :limit => STEP, :offset => offset).each { |item|
                o = dest.new(item.attributes)
                o.id = item.id
                o.save
              }
            }
          }
        }
      }
    end
  end
end