ruby on rails - Best way to get a list of parent IDs -

ruby on rails - Best way to get a list of parent IDs -

i have these models in rails app:

class course of study < 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

now want quizsubmissions' course of study id, i.e.quiz_submission.quiz.part.topic.course.id each quiz_submission.

my current code quizsubmission.all.map{|qs| qs.quiz.part.topic.cours.id} insanely slow, have tried joins, still did not improve performance. maybe used joins wrongly.

any suggestions? should create quizsubmission belongs_to :course? thanks!

you can do:

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

ruby-on-rails ruby