ActiveAdmin.default_sort_order "id_desc" prevents use of scopes with joins

[urbanautomaton]

Hi,

I'm using a model with some scopes involving joins. For example:

class User < ActiveRecord::Base
...
  def self.popular
    joins('LEFT JOIN followings ON users.id = followings.followee_id').
    group('users.id').
    where('COUNT(users.id) > 10')
  end
...
end

If I add this scope to my ActiveAdmin config, I get the following error when viewing the Users index:

Mysql2::Error: Column 'id' in order clause is ambiguous: SELECT COUNT(*) AS count_all, users.id AS users_id FROM `users` LEFT JOIN followings ON users.id = followings.followee_id GROUP BY users.id WHERE COUNT(users.id) > 10 ORDER BY id desc

This appears to be because in lib/active_admin.rb the default sort order is set to "id_desc", which doesn't then get scoped with the appropriate table name - hence the ambiguous query error.

There's a gist here with the full stack trace in case it's useful...

Cheers,
Simon

p.s. thanks for a wonderful tool, by the way - I'm really loving what I've seen of it so far.