Reorder as a concern

gistfile1.rb

module IsOrderable
 extend ActiveRecord::Concern
 
 def change_position_to(n)
   safe_n = self.class.sanitize(n)
   current_position = self.class.sanitize(position)
   connection.execute(<<-SQL
    BEGIN;
    UPDATE #{self.class.table_name} SET position = position + 1 WHERE parent_id = #{parent_id} AND position < #{current_position} AND position >= #{safe_n};
    UPDATE #{self.class.table_name} SET position = position - 1 WHERE parent_id = #{parent_id} AND position > #{current_position} AND position <= #{safe_n};
    UPDATE #{self.class.table_name} SET position = #{safe_n} WHERE id = #{id};
    COMMIT;
   SQL)
 end
end

class Foo < ActiveRecord::Base
 include IsOrderable
end

Foo.find(id).change_position_to(4)

Foo.order(position: :asc)