소개

표 구성

모델 구성

#### item.rb ####
class Item < ActiveRecord::Base
  belongs_to :order
end

#### order.rb ####
class Order < ActiveRecord::Base
  has_many :items
  has_many :reviews
end

#### review.rb ####
class Review < ActiveRecord::Base
  belongs_to :order
  has_many :themes
end

#### theme.rb ####
class Theme < ActiveRecord::Base
  belongs_to :review
end

다양한 구현

다단Association

order에서 theme을 2단 has_many 하고 싶다 & theme에서 order를 2단 belongs_to 하고 싶다

#### order.rb ####
class Order < ActiveRecord::Base
  # ...
  has_many :themes, through: :reviews
end

#### theme.rb ####
class Theme < ActiveRecord::Base
  # ...
  delegate :order, to: :reviews
end

pry(main)> Theme.last.order
  Theme Load (0.4ms)  SELECT  `reviews`.* FROM `reviews` ORDER BY `reviews`.`id` DESC LIMIT 1
  Review Load (0.3ms)  SELECT  `reviews`.* FROM `reviews` WHERE `reviews`.`id` = 1 LIMIT 1
  Order Load (0.5ms)  SELECT  `orders`.* FROM `orders` INNER JOIN `reviews` ON `reviews`.`id` = `orders`.`review_id` WHERE `orders`.`review_id` = 1 LIMIT 1

다단 Scope(다단 Joins)

item을 review.text로 sort하고 싶습니다.

#### item.rb ####
class Item < ActiveRecord::Base
  # ...
  scope :join_reviews, -> { joins(:order, order: :reviews) }
end

pry(main)> Item.all.order("review.theme_id desc")
  Item Load (7.0ms)  SELECT  `items`.* FROM `items` INNER JOIN `orders` ON `orders`.`id` = `items`.`order_id` INNER JOIN `reviews` ON `reviews`.`order_id` = `orders`.`id` ORDER BY reviews.text DESC

delegate 위험설(2019-09-15갱신)

참고