撷取模型属性

Question

我有型号：

class Exam < AR::Base 
    has_many :questions_in_exams 
    has_many :questions, :through => :questions_in_exams 
end 

class QuestionsInExam < AR::Base 
    belongs_to :examination 
    belongs_to :question 
    # This model also has a "question_index" attribute 
end 

class Question < AR::Base 
    has_many :questions_in_exams 
    has_many :examinations, :through => :questions_in_exams 
end 

鉴于考试的一个实例，我要取的是它是从加盟模式的额外 属性一起问题（如“question_index”）。我怎样才能做到这一点？

如果我做的：

e = Examination.find(1) 
questions = e.questions 

然后在问题的数组元素不会有 “question_index” 属性

我想我可以这样写：

e = Examination.find(1) 
questions = e.questions_in_exam(:include => "question") 

但这似乎不如此优雅，因为我需要的大部分数据都在Question模型上， ，但返回的数组将包含QuestionInExam实例。

任何想法？

感谢

Answer 1

开始从问题的模型，像这样

Question.select("questions.*, examination.id") 
     .joins(:questions_in_exam => :examination) 
     .where("examinations.id=?", 1) 

# Note that inside "select" you can specified all the attributes you want from any of the joined models. 

一旦你高兴与您的查询其转换为scope

，并最终调用可能是这个样子：Question.for_exam（1）