问Rails 3事务，回滚所有内容

EN

class Bear < ActiveRecord::Base
    def feed!
      self.transaction do
          raise Exception unless self.foods_eaten << Food.new(:name => "fish")
          self.fed_at = Time.now
          save!
       end
    end
end

class Hippo < ActiveRecord::Base
    def wash!
        self.transaction do
            @soap.inventory -= 1
            @soap.save!
            self.washed_at = Time.now
            save!
        end
    end
end

class ZookeeperController < ApplicationController

    def chores
        @zookeeper = Zookeeper.find(params[:id])
        Animal.transaction do
            begin
                @hippo.wash!
                @bear.feed!    # => FAIL AT THIS LINE
                @zookeeper.finished_at = Time.now
                @zookeeper.save!
                redirect_to chores_completed_path
            rescue Exception => e
                 render "new_chores"
            end
        end
    end
end