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.

Community · Accepted Answer · 2017-05-23 12:04:48Z

4

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')
}

edited May 23, 2017 at 12:04

CommunityBot

11 silver badge

answered Feb 3, 2013 at 18:41

Raindal

3,23717 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

daspianist Over a year ago

Typing in the code as seen above resulted in a "tried to create Proc object without a block" error. After seeing a similar issue raised, I reformatted the code as

scope :by_most_popular, lambda { |course|      joins(:question).order('questions_count DESC, question.answers_count DESC, created_at DESC')   }

. However, now Ruby is complaining that "wrong number of arguments (0 for 1)"

Raindal Over a year ago

Updated my answer to replace "do...end" with curly brackets. Do you have more precisions regarding the "wrong number of arguments error (0 for 1)" ?

daspianist Over a year ago

I did a bit more digging around to find out whats behind the "wrong arguments" error. I rewrote a simpler scope method to test if the joins is working (scope :by_answer_count, -> { joins(:question).order('question.answers_count DESC') }) and I got the error "Association named 'question' was not found; perhaps you misspelled it?". Given the way the models are related, i don't see why its can't find the question model. I think its likely this was throwing the more complex sorting method off.

Raindal Over a year ago

Maybe it's :questions and not :question given the has_many relation ?

Raindal Over a year ago

My mistake, I think you don't need to pass the argument (as your first error said) juste remove the |course|. It is used in case you pass an argument to your scope... sorry about that

|

Collectives™ on Stack Overflow

Multi-layer sorting in Rails model

1 Answer 1

10 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

10 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related