我如何級聯保存與mongoid的has_and_belongs_to_many關係？

Question

我有一個標籤和一個問題類。

class Question 
    include Mongoid::Document 
    include Mongoid::Timestamps 
    identity type: String 
    has_and_belongs_to_many :tags # Refer to tag_ids 
end 

class Tag 
    include Mongoid::Document 
    identity type: String  
    has_and_belongs_to_many :questions 
end 

然而，當我做了以下標籤不保存：

t = Tag.new(id: "politics") 
q = Question.new({tags: [t]}) 
q.save! 

然而，當我這樣做是創建的標籤：

Question.create!({tags: [Tag.new(id: "politics")]}) 

Answer 1

如果我這樣做了之後，那麼它會正常工作：

has_and_belongs_to_many :tags, autosave: true # Refer to tag_ids