Rails 4:显示第三级关联中的项目列表

Question

我在我的rails应用程序中有以下结构.

class Country < ActiveRecord::Base
  has_many :states
end

class State < ActiveRecord::Base
  has_many :cities
  belongs_to :country
end

class City < ActiveRecord::Base
  belongs_to :state
end

我想从乡村模式访问城市.例如@country.cities.另外,我怎样才能从城市模型中获得国家？例如@city.country

谢谢,

Answer 1

使用has_many中的选项和belongs_to的委托:

class Country < ActiveRecord::Base
  has_many :states
  has_many :cities, through: :states
end

class State < ActiveRecord::Base
  has_many :cities
  belongs_to :country
end

class City < ActiveRecord::Base
  belongs_to :state
  delegate :country, to: :state
end