Ruby on rails: How to display a hierarchical list?

Question

Ruby on Rails

You need to create a nested category hierarchy in your project.
Migration:

class CreateCategories < ActiveRecord::Migration
  def change
    create_table :categories do |t|
      t.string :title
      t.references :parent, index: true
      t.timestamps null: false
    end
  end
end

According to the model:

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

  belongs_to :parent, class_name: "Category"


end

(material taken from here )
Actually the question is: How to check if a category has subordinates and, if so, display them?
PS at least kick in the place where you can read about it for the noob

Answer 1

The following code worked correctly:

<% if category.subordinates.count >=1 %>
          <%= category.subordinates.first.title %>
              <% end %>

accordingly, subordinates contains many objects (based on the has_many relation), which means that the category.subordinates.title expression is incorrect (we request 1 title from many objects). Conclusion: parsing subordinates through each