I am running into a problem with to_json not rendering my virtual attributes

class Location < ActiveRecord::Base
    belongs_to :event
    before_create :generate_oid
    validates_associated :event

    attr_accessor :event_oid

    def event_oid
      @event_oid = event.oid
    end
end

event_oid is not part of the array returned by:

Location.first.attributes

This is particularly a problem for me when using to_json that automatically serializes record attributes to jason. to_json omits my virtual attribute.

How can you make a virtual attribute treated as an actual instance attribute?

Edit:

to_json is just an example of a method where having my virtual attribute treated as an actual attribute would be nice.