# app/helpers/adults_helper.rb
module AdultsHelper
  def say_hello
    "hello,world!"
  end
end

# app/models/adult.rb
class Adult < ActiveRecord::Base
  include AdultsHelper

end

在控制台中测试

$script/console
>> a = Adult.new
# => #<Adult id:...>
>> a.say_hello
# => "hello,world!"