Add Comment model and nested route

Add Comment model and migration with a foreign key reference to the
Article model. Make the comment a nested resource under the Article
resource so that each comment resource requires an :article_id parameter
in the URL.

Add has_many association in the Article model and include the dependent:
:destroy option so that the Article destroy tests don't fail.

Completes Rails Getting Started Guide:
* 8 Adding a Second Model
  * 8.1 Generating a Model
  * 8.2 Associating Models
  * 8.3 Adding a Route for Comments

app/models/article.rb

@@ -1,4 +1,6 @@
 class Article < ApplicationRecord
+  has_many :comments, dependent: :destroy
+
   validates :title, presence: true
   validates :body, presence: true, length: { minimum: 10 }
 end

app/models/comment.rb

@@ -0,0 +1,3 @@
+class Comment < ApplicationRecord
+  belongs_to :article
+end

config/routes.rb

@@ -1,6 +1,9 @@
 Rails.application.routes.draw do
   root "articles#index"
 
-  resources :articles
+  resources :articles do
+    resources :comments
+  end
+
   resources :posts
 end

db/migrate/20211229220150_create_comments.rb

@@ -0,0 +1,11 @@
+class CreateComments < ActiveRecord::Migration[7.0]
+  def change
+    create_table :comments do |t|
+      t.string :commenter
+      t.text :body
+      t.references :article, null: false, foreign_key: true
+
+      t.timestamps
+    end
+  end
+end

test/fixtures/comments.yml

@@ -0,0 +1,16 @@
+# Read about fixtures at https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
+
+nerd_gm:
+  commenter: Nerdy Game Master
+  body: I love how i can do something like NerdDice.roll_4d6_with_advantage_3 and it just works!
+  article: nerd
+
+nerd_ruby:
+  commenter: Ruby Enthusiast
+  body: Thanks for the episode on method_missing and Ruby metaprogramming! It really helped me out.
+  article: nerd
+
+why_visionary:
+  commenter: Visionary
+  body: That Start With Why video is my favorite TED talk!
+  article: why

test/models/comment_test.rb

@@ -0,0 +1,7 @@
+require "test_helper"
+
+class CommentTest < ActiveSupport::TestCase
+  # test "the truth" do
+  #   assert true
+  # end
+end