How to sort Rails AR.find by number of objects in a has_many relationship

Question

How can I write an AR find query to have the results ordered by the number of records in a has_many association?

class User < ActiveRecord::Base
  has_man         


        

Answer 1

The easiest way to achieve this is probably to add a counter cache to that model and then sort by that column.

class Photo < ActiveRecord::Base
  belongs_to :user, :counter_cache => true
end

And be sure to add a column to your users table called photos_count.

Then you will be able to...

User.find(:all, :order => 'photos_count')