Rails2.1中的新东西之一: has-one-through

Ryan Daigle发布了一系列关于rails2.1中新特性的文章.这里是这个系列中的一篇.

Has one :through

has_one终于长得和has_many一样高了,它也支持了:through选项.

class Magazine < ActiveRecord::Base
  has_many :subscriptions
end

class Subscription < ActiveRecord::Base
  belongs_to :magazine
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :subscriptions
  has_one :magazine, :through => : subscriptions, :conditions => ['subscriptions.active = ?', true]
end

并且当through属性改变后,中间属性会随之改变

@ryan.subscriptions #=> []
@ryan.magazine = Magazine.create(:name => 'Hustler')
@ryan.subscriptions #=> [<Subscription magazine_id: 1, user_id: 1 ...>]

译者注: 当through连接有多个record,has_one会返回第一个.
Rails2.1中的新东西之三: Dirty Objects
Rails2.1中的新东西之二: Gem Dependencies
Rails2.1中的新东西之一: has-one-through