Dynamically added hash properties to Rails Model instance object?

Question

There is a model

class PlaylistModel < ActiveRecord::Base
    /* code */
end

And then in a controller action there is code like this

PlaylistController < ActionController::Base
  def a_action
    @item = Playlist.find(10)
    @item[:visited] = true     
  end
end

However there is no visited attribute defined in PlaylistModel (or in the schema for the playlist table)! It looks like a new attribute is being dynamically added to the object. Is this what is going on and where is all this functionality defined / where can I read more about it.

Thanks for the help!

Answer 1

This is the attribute setter shortcut as explained here. It is pretty much equivalent to:

@item.attributes[:visited] = true

Answer 2

I think what you're looking for though is virtual attributes... which can be defined in the model http://railscasts.com/episodes/16-virtual-attributes