如何在Ruby on Rails中遍历自引用模型

class Category < ApplicationRecord
  belongs_to :parent, class_name: "Category", optional: true
  has_many :children, class_name: "Category", foreign_key: "parent_id"
end

class Category < ApplicationRecord
  # ...

  def traverse
    traverse_children(self)
  end

  private

  def traverse_children(category)
    category.children.each do |child|
      traverse_children(child)
    end
  end
end

class CategoriesController < ApplicationController
  def index
    @categories = Category.all
    @categories.each do |category|
      category.traverse
    end
  end
end