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

If you don't want an extra column, you could always ask for an extra column in the returned result set:

User.all(:select => "#{User.table_name}.*, COUNT(#{Photo.table_name}.id) number_of_photos",
         :joins => :photos,
         :order => "number_of_photos")

This generates the following SQL:

SELECT users.*, COUNT(photos.id) number_of_photos
FROM `users` INNER JOIN `photos` ON photos.user_id = users.id
ORDER BY number_of_photos