gistfile1.rb

require 'yaml'
require 'active_record'

class ActiveRecord::Migrator
  class << self
    TARGET_METHODS = %w[up down]

    TARGET_METHODS.each do |name|
      define_method("#{name}_with_database_dump") do |*args|
        dump_current_database
        self.send("#{name}_without_database_dump", *args)
      end
      alias_method_chain name, :database_dump
    end

    def dump_current_database
      config_path = File.join(RAILS_ROOT, 'config', 'database.yml')
      db = YAML::load(ERB.new(IO.read(config_path)).result)[RAILS_ENV]
      identifier = Time.now.utc.strftime("%Y%m%d%H%M%S")

      case db['adapter']
      when 'mysql'
        file = "#{RAILS_ROOT}/tmp/#{RAILS_ENV}_dump_#{identifier}.sql.bz2"
        puts "## dump database to [#{file}]"
        system("mysqldump -u #{db['username']} --password=#{db['password']} --add-drop-table #{db['database']} | bzip2 -c > #{file}")
      end
    end

  end
end