Multi-layer sorting in Rails model

Question

Im having trouble figuring out how to write a multi-layer sort using a scope method in my model, which can sort through the model's attributes, as well as its related child models' attributes?

To put more concretely, I have the following models, each a related child of the previous one (I excluded other model methods and declarations for brevity):

class Course < ActiveRecord::Base 
  has_many :questions
  # would like to write multi-layer sort here 
end 

class Question < ActiveRecord::Base 
  belongs_to :course, :counter_cache => true
  has_many: :answers

end 

class Answer < ActiveRecord::Base 
  belongs_to :question, :counter_cache => true
end

I would like to sort courses first by questions_count (through my counter_cache), then by answer_count, and lastly by created_at, and was wondering how I could string everything together into a single scope method to put in my Course model.

Thanks.

Answer 1

As seen here (creating a scope with a joined model) : problem: activerecord (rails3), chaining scopes with includes

And here (sorting with multiple columns) : Ruby on Rails: how do I sort with two columns using ActiveRecord?

And finally here (sorting by associated model) : Rails 3. sort by associated model

You may achieve this like so :

scope :complex_sorting, lambda {
    joins(:questions)
    .order('questions_count DESC, question.answers_count DESC, created_at DESC')
}