previous_changes方法

[27] pry(main)> c = Channel.find 6
=> #<Channel id: 6, title: "会员", cid: "96", pid: "", channel_position: "", data_type: "", filter_id: "", version: "1.2.0">
[28] pry(main)> c.valid?
=> true
[29] pry(main)>
[30] pry(main)>
[31] pry(main)> c.has_filter
=> "1"
[32] pry(main)> c.cid
=> "96"
[33] pry(main)> c.is_default_channel
=> "1"
[34] pry(main)> c.reload
=> #<Channel id: 6, title: "会员", cid: "96", pid: "", channel_position: "", data_type: "", filter_id: "", version: "1.2.0">
[35] pry(main)> c.previous_changes
=> {}
[36] pry(main)> c.title = c.title + 1
TypeError: no implicit conversion of Fixnum into String
from (pry):43:in `+'
[37] pry(main)> c.title = c.title + '1'
=> "会员1"
[38] pry(main)> c.save
=> true
[39] pry(main)> c.previous_changes
=> {"title"=>["会员", "会员1"], "updated_at"=>[Fri, 08 Apr 2016 08:10:30 CST +08:00, 2016-04-08 12:28:20 +0800]}
[40] pry(main)> a, b = [1,2]
=> [1, 2]
[41] pry(main)> a
=> 1
[42] pry(main)> b
=> 2

 model里的private方法

def update_auto_activate_job
      if active?  # 对已经设置了自动开启时间的视频进行手动开启操作
        if (change = previous_changes[:state]) && change[0] == 0
          if job = Sidekiq::ScheduledSet.new.find_job(auto_activate_job_id)
            job.delete
          end

          update_attributes auto_activated_at: nil, auto_activate_job_id: nil 
        end
      else  # 针对未开启的视频，设置，取消或者更新定时开启时间
        if change = previous_changes[:auto_activated_at]
          original_value, new_value = change

          if original_value.nil?  # 设置定时开启,id是当前model里的id
            job_id = AutoActivateWorker.perform_at new_value, id
            update_attribute :auto_activate_job_id, job_id
          elsif new_value.nil?  # 取消定时开启
            if job = Sidekiq::ScheduledSet.new.find_job(auto_activate_job_id)
              job.delete
            end

            update_attribute :auto_activate_job_id, nil 
          else # 更新定时开启时间
            if job = Sidekiq::ScheduledSet.new.find_job(auto_activate_job_id)
              job.reschedule new_value
            end
          end
        end
      end 
    end