Symlinking ActiveRecord Objects

Have you ever needed one object to act like another one? To symlink an object? In Rails it is quite easy to accomplish. Simply add a symlink_id integer field to your database table and use the following code.

class SomeObject < ActiveRecord::Base
  def id
    return symlink_id? ? super : symlink_id
  end

  def symlink(obj)
     update_attribute :symlink_id, obj.id
  end
end

There are many uses for this idea, but unfortunately I can’t reveal my use at the moment. Feel free to post comments with ideas though.

A notable limit to this code is that you can’t symlink objects that aren’t also SomeObject. It is possible to accomplish this as well however. In addition to symlink_id, add a varchar symlink_kind.

class SomeObject < ActiveRecord::Base
  class << self
    def find(*args)
      obj = super(*args)
      if obj.is_a? Array
        obj.map{|o| o.symlink_kind? && o.symlink_id? ? eval(o.symlink_kind+'.find('+o.symlink_id+')') : o }
      else
        obj.symlink_kind? ? eval(obj.symlink_kind+'.find('+obj.symlink_id+')') : obj
      end
    end
  end

  def symlink(obj)
     self.symlink_id = obj.id
     self.symlink_kind = obj.class.to_s
     save
  end
end