如何在ActiveRecord模型中存儲要在回調中使用的數據

Question

用戶可以將多個預定義的events分配給room但是，有時它們可​​能會在運行中創建新的events。

我想捕捉這些新的事件，並將它們添加到一個單獨的表userevent

下面是我的做法。我試圖將after_save中不存在的所有事件保存到:user_events，然後回調add_new_events_to_userevents。

after_save :add_new_events_to_userevents 
    attr_reader :event_tokens, :user_events 
    attr_accessible :user_events #not real column in table 
    attr_accessible :fulladdress, :title, :description, :cost, :email, :maximum_capacity, :phone, :user_id, :property_id 

    def add_new_events_to_userevents 
    print "total new events:" + self.user_events.size 
    self.user_events.each do |i| 
     u = Userevent.new 
     u.name = i 
     u.approved = false 
     u.room_id = self.id 
     u.user_id = self.user_id 
     u.save 
    end 
    end 

    def event_tokens=(ids) 
    events = ids.split(',') 
    allowed_events = [] 
    userevents = [] 
    events.each do |i| 
     i = i.strip 
     events = Event.select(:id).where("upper(name) = ?", i.upcase); 
     event = (events.blank? ? nil : events.first) 
     if event.present? 
     allowed_events << event[:id] 
     else 
     userevents << i 
     end 
    end 
    self.event_ids = allowed_events #these are events that exist 
    self.user_events = userevents #these are new events, need them in after_save 
    end 

我得到一個錯誤

You have a nil object when you didn't expect it! 
You might have expected an instance of Array. 
The error occurred while evaluating nil.size 

• 我怎麼能存儲所有新用戶事件，然後在我的after_save回調使用它們？
• 在after_save回撥如果我打電話self.id和self.user_id會給我id和user_id剛剛保存到數據庫的記錄？

Answer 1

看起來像打印語句斷行，如果你沒有一個用戶定義的user_events ... 添加一個if語句來它，使其工作..

print "total new events:" + self.user_events.size if user_events