class Document < ActiveRecord::Base
  include AASM

  aasm do  
    state :unread,:initial => true
    state :read
    state :closed

    event :view do
      transitions :to => :read,:from => [:unread]
    end

    event :close do
      transitions :to => :closed,:from => [:read,:unread]
    end
  end

现在在我的控制台上：

➜  ✗ bundle exec rails c
Loading development environment (Rails 3.2.2)
irb(main):006:0> Document.create!(:title => 'test')
   (0.2ms)  BEGIN
  sql (0.3ms)  INSERT INTO `documents` (`aasm_state`,`checklist_id`,`created_at`,`description`,`dir`,`planned_date`,`procedure_id`,`section`,`subsection`,`title`,`updated_at`) VALUES (0,NULL,'2012-06-16 20:03:18','test','2012-06-16 20:03:18')
   (0.4ms)  COMMIT
=> #<Document id: 28,title: "test",description: nil,dir: nil,section: nil,subsection: nil,planned_date: nil,procedure_id: nil,checklist_id: nil,created_at: "2012-06-16 20:03:18",updated_at: "2012-06-16 20:03:18",aasm_state: 0>
irb(main):007:0> doc = Document.last
  Document Load (0.3ms)  SELECT `documents`.* FROM `documents` ORDER BY `documents`.`id` DESC LIMIT 1
=> #<Document id: 28,aasm_state: 0>
irb(main):008:0> doc.view!
NoMethodError: undefined method `name' for nil:NilClass
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/supporting_classes/state.rb:15:in `=='
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/aasm.rb:143:in `aasm_state_object_for_state'
    from (irb):8:in `find'
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/aasm.rb:143:in `each'
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/aasm.rb:143:in `find'
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/aasm.rb:143:in `aasm_state_object_for_state'
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/aasm.rb:158:in `aasm_fire_event'
    from /Library/Ruby/Gems/1.8/gems/aasm-3.0.6/lib/aasm/base.rb:48:in `view!'
    from (irb):8

正如你所看到的,我一直在努力

undefined method `name’ for nil:NilClass

我正在使用Ruby 1.8.7.