如何使用ruby on ruby on rails中的小类

# app/models/post.rb
class Post < ApplicationRecord
  has_many :comments
end

# app/models/comment.rb
class Comment < ApplicationRecord
  belongs_to :post
end

# config/routes.rb
Rails.application.routes.draw do
  resources :posts do
    resources :comments
  end
end

# app/controllers/comments_controller.rb
class CommentsController < ApplicationController
  before_action :set_post
  before_action :set_comment, only: [:show, :edit, :update, :destroy]

  def index
    @comments = @post.comments
  end

  def new
    @comment = @post.comments.new
  end

  def create
    @comment = @post.comments.new(comment_params)
    if @comment.save
      redirect_to post_comments_path(@post), notice: 'Comment was successfully created.'
    else
      render :new
    end
  end

  def show; end

  def edit; end

  def update
    if @comment.update(comment_params)
      redirect_to post_comment_path(@post, @comment), notice: 'Comment was successfully updated.'
    else
      render :edit
    end
  end

  def destroy
    @comment.destroy
    redirect_to post_comments_path(@post), notice: 'Comment was successfully destroyed.'
  end

  private

  def set_post
    @post = Post.find(params[:post_id])
  end

  def set_comment
    @comment = @post.comments.find(params[:id])
  end

  def comment_params
    params.require(:comment).permit(:body)
  end
end

resources :posts do
  resources :comments, shallow: true
end