Suggestion: Allowing ordering to accept more options

Created by: migu0

I have to order the index page by default by an attribute quality, which can be NULL or any value from 0 to 10.

module Admin
  class OrganizationsController < Admin::ApplicationController

    private

    def order
      @_order ||= if params[:order]
        Administrate::Order.new(params[:order], params[:direction])
      else
        Administrate::Order.new('quality', 'desc NULLS last')
      end
    end
  end
end

If I order with desc (highest quality first), NULL's will come first. Postgres has a nice syntax to control whether NULL's should come first or not: Organization.all.order('quality DESC NULLS last').

However, I can't use the code posted above because AR is not aware of this Postgres syntax when attribute and order is passed in as a key / value like so: https://github.com/thoughtbot/administrate/blob/master/lib/administrate/order.rb#L10. I get the following error: Direction "desc NULLS last" is invalid. Valid directions are: [:asc, :desc, :ASC, :DESC, "asc", "desc", "ASC", "DESC"]

However, if we changed this line to accept any SQL ordering (without AR validating it), it would work: relation.order("#{attribute} #{direction}")