最佳方式

Question

我在我的Rails应用这些模型：

class Course < ActiveRecord::Base 
    has_many :topics 
end 

class Topic < ActiveRecord::Base 
    has_many :parts 
    belongs_to :course 
end 

class Part < ActiveRecord::Base 
    has_many :quizzes 
    belongs_to :topic 
end 

class Quiz < ActiveRecord::Base 
    has_many :quiz_submissions 
    belongs_to :part 
end 

class QuizSubmission < ActiveRecord::Base 
    belongs_to :quiz 
end 

现在我想所有QuizSubmissions'课程ID，即quiz_submission.quiz.part.topic.course.id每个quiz_submission。

我目前的代码是QuizSubmission.all.map{|qs| qs.quiz.part.topic.cours.id}这是非常慢，我也试过joins，仍然没有提高性能。也许我错误地使用了joins。

有什么建议吗？我应该让QuizSubmission belongs_to :course？谢谢！

Answer 1

你可以这样做：

QuizSubmission.joins(:quiz => {:part => {:topic => :course}}). 
       select('quiz_submissions.id, courses.id as course_id') 

Answer 2

您可以尝试

Course.joins({ topics: { parts: { quizzes: :quiz_submissions } } }).map(&:id) 

Answer 3

如果我理解正确的问题，那就是如何让IDS快速不加入。

quiz_subm_ids = QuizSubmission.pluck(:id) 
part_ids = Part.where(quiz_submission_id: quiz_subm_ids).pluck(:id) 
topic_ids = Topic.where(part_id: part_ids).pluck(:id) 
course_ids = Topic.where(topic_id: topic_ids).pluck(:id)