ruby>>
class Parts < ActiveRecord::Base # STI
end

class Parts::Image < Parts
end

part = Parts::Image.create!
p part[:type]
<<ruby

で何が返るのかの話。

before 2.1

ruby>>
part[:type] # => "Image"
<<ruby

after 2.1

ruby>>
part[:type] # => "Parts::Image"
<<ruby

互換性

2.1 では AR::Base.sti_name メソッドが返す値を利用しており、
AR::Base.store_full_sti_class で制御できる。

ruby>>
Parts::Image.store_full_sti_class # => true
Parts::Image.sti_name # => "Parts::Image"
Parts::Image.create[:type] # => "Parts::Image"

Parts::Image.store_full_sti_class = false
Parts::Image.sti_name # => "Image"
Parts::Image.create[:type] # => "Image"
<<ruby

応用

2.1 のSTIを利用するとナベアツな世界を簡単に作成できる。

ruby>>
class Person < ActiveRecord::Base; end
class Nabe < Person; end
class Aho < Person; end
def Person.sti_name
Time.now.day % 3 == 0 ? "Aho" : "Nabe"
end

(1..3).map{ Nabe.create[:type] }
=> ["Nabe", "Nabe", "Nabe"]

Stub

class Time
def day
3
end
end

(1..3).map{ Nabe.create[:type] }
=> ["Aho", "Aho", "Aho"]
<<ruby