Adding a second generator to a gem

second_generator.rb

require 'rails/generators/migration'

# must be placed in the gem's dir 'lib/generators/my_gem/second/second_generator.rb'
module MyGem

  # TODO: this module tries to DRY up a bit, should be elsewhere in
  # its own file
  module MigrationGenerator
    def self.included(base)
      base.extend(ClassMethods)
    end
    module ClassMethods
      def next_migration_number(path)
        unless @prev_migration_nr
          @prev_migration_nr = Time.now.utc.strftime("%Y%m%d%H%M%S").to_i
        else
          @prev_migration_nr += 1
        end
        @prev_migration_nr.to_s 
      end
    end 
  end 
    
  module Generators
    class SecondGenerator < ::Rails::Generators::Base
      include Rails::Generators::Migration
      include MyGem::MigrationGenerator
      source_root File.expand_path('../templates', __FILE__)
      desc "do the second thing"
      
      def copy_migrations
        migration_template "create_things.rb", "db/migrate/create_things.rb"
      end
    end
  end
end