Question

我在Rails应用程序中有这些模型：

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

现在我想获得所有QuizSubmissions的课程ID，即每个quiz_submission的quiz_submission.quiz.part.topic.course.id。

我当前的代码是QuizSubmission.all.map{|qs| qs.quiz.part.topic.cours.id}，这个代码非常慢，我也尝试了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QuizSubmission belongs_to :course吗？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

你可以尝试

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

Answer 3

如果我理解了问题，那就是如何在没有加入的情况下快速获得ID。

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)

获取父ID列表的最佳方法

3 个答案: