如何在Rails 4中使用自引用控制器實現父類別，類別和子類別

Question

我正在嘗試使用自引用實現三級深度關聯。

Cat1
    Sub1
        SubSub1
        SubSub2
    Sub2
Cat2
    Sub1
Cat3
    Sub1
    Sub2
        SubSub1

我可以通過此關系獲取類別的子類別：

class Category < ActiveRecord::Base
  has_many :sub_categories, class_name: "Category", foreign_key: :parent_id
end

當我只有兩級深度類別時，這很好。 對於使用自引用的三層深度關聯，我嘗試使用此關系，但未獲得所需的輸出。

class Category < ActiveRecord::Base
  belongs_to :parent_category, class_name: "Category"
  has_many :sub_categories, class_name: "Category", foreign_key: :parent_id
end

這是我使用此association.find Category.find(3).parent_category的結果。

2.0.0-p648 :012 > Category.find(2)
  Category Load (1.2ms)  SELECT `categories`.* FROM `categories` WHERE `categories`.`id` = 2 LIMIT 1
 => #<Category id: 2, title: "Suit", description: "sffdsfsxcx ssdfvvs", seo_name: "sfsdf", parent_id: nil, hoe_page: nil, status: true, sequence: "1", banner_image_file_name: nil, banner_image_content_type: nil, banner_image_file_size: nil, banner_image_updated_at: nil, image_file_name: nil, image_content_type: nil, image_file_size: nil, image_updated_at: nil, home_description: "adhkadaa", home_page: true, long_description: "sdfsddfffssssde", created_at: "2018-04-09 07:42:55", updated_at: "2018-04-09 07:42:55"> 
2.0.0-p648 :013 > Category.find(3)
  Category Load (1.1ms)  SELECT `categories`.* FROM `categories` WHERE `categories`.`id` = 3 LIMIT 1
 => #<Category id: 3, title: "a", description: "aaa", seo_name: "a", parent_id: 2, hoe_page: nil, status: true, sequence: "1", banner_image_file_name: nil, banner_image_content_type: nil, banner_image_file_size: nil, banner_image_updated_at: nil, image_file_name: nil, image_content_type: nil, image_file_size: nil, image_updated_at: nil, home_description: "aaa", home_page: true, long_description: "aaa", created_at: "2018-04-09 09:44:11", updated_at: "2018-04-09 09:44:11"> 
2.0.0-p648 :014 > Category.find(3).parent_category
  Category Load (1.1ms)  SELECT `categories`.* FROM `categories` WHERE `categories`.`id` = 3 LIMIT 1
 => nil 

請在這里幫助我，讓我了解對我而言什么是完美的聯想。 請不要給我寶石名稱，例如“祖先”或“ awesome_nested_set”，我需要純Rails關聯。

Answer 1

嘗試這個：

  belongs_to :parent_category, foreign_key: :parent_id, class_name: 'Category'
  has_many :sub_categories, foreign_key: :parent_id, class_name: 'Category'