的has_many或belongs_to的工作錯

Question

我有這兩種型號：

class Answer < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :question 
    has_many :edits, dependent: :destroy 
end 

class Question < ActiveRecord::Base 
    belongs_to :user 
    has_many :answers, dependent: :destroy 
end 

但是，當我在軌控制檯寫入以下內容：

q=Question.new 
q.save 

a=Answer.new 
a.question = q 
a.save 

q.answers.size 

它給了我零。

irb(main):026:0> q.answers.size 
    => 0 

但是，當我寫這篇文章：

Answer.where(:question_id => q.id).size 

它給了我1

SO我該怎麼辦？

情況下你需要它 - 答案和問題遷移：

class CreateAnswers < ActiveRecord::Migration 
    def change 
    #execute "DROP TABLE #{:answers} CASCADE" 

    create_table :answers do |t| 
     t.text :body 
     t.references :user, index: true, foreign_key: true 
     t.references :question, index: true, foreign_key: true 

     t.timestamps null: false 
    end 
    end 
end 

class CreateQuestions < ActiveRecord::Migration 
    def change 
    #execute "DROP TABLE #{:questions} CASCADE" 
    create_table :questions do |t| 
     t.string :title 
     t.text :body 
     t.references :user, index: true, foreign_key: true 

     t.timestamps null: false 
    end 
    end 
end 

Answer 1

你需要在你的關係inverse_of選項來使用。

class Answer < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :question, inverse_of: answers 
    has_many :edits, dependent: :destroy 
end 

class Question < ActiveRecord::Base 
    belongs_to :user 
    has_many :answers, inverse_of: question, dependent: :destroy 
end 

所以，當你這樣做：

a.question = q 

Rails會爲你做這個（在內存中）：

q.answers << a 

而且你不需要重新加載Q值。