Order parent model using children in rails

Question

I have model product and vote, I need to order products by votes count DESC.

product has_many :votes, vote belongs_to :product

index_controller.rb

def index
  @products = Product.all
end

possible duplicate of [Rails order by results count of has\_many association](http://stackoverflow.com/questions/16996618/rails-order-by-results-count-of-has-many-association) — Puce, Jun 23 '15 at 12:26
You may not want it, but you're going to be full-scanning the product table and joining to the foreign key for every row in the votes table without it. With an index on the counter cache column of the product table you'll get an index range scan on any decent relational database. — David Aldridge, Jun 23 '15 at 12:42

Ganesh Kunwar · Accepted Answer · 2015-06-23T13:02:01.263

0

@products = Product.order("count(votes) DESC")

If you have not votes column then use:

@products = Product.all.sort { |a, b| b.votes.count <=> a.votes.count   }

edited Jun 23 '15 at 13:02

answered Jun 23 '15 at 12:30

Ganesh Kunwar

But how can i preform DESC sorting? – Jun 23 '15 at 12:52
Just use Sort instead of Sort. I have updated my answer. look – Ganesh Kunwar Jun 23 '15 at 13:02
Yeah, it is actually works, but can you say few words about how it works? – Jun 23 '15 at 13:05

1 Answers1