bundle exec rails generate migration create_comment_users

class CreateCommentUsers < ActiveRecord::Migration
   def change
     create_table :comment_users do |t|
       t.string :username
       t.string :password
       t.timestamps
     end
   end
 end

bundle exec rails generate migration add_comment_user_id_to_comments

add_reference :comments, :comment_user_id, :integer

# app/controllers/comment_users_controller.rb

class CommentUsersController < ApplicationController
  def new
     @comment_user = CommentUser.new
   end

   def create
     @comment_user = CommentUser.new
     @comment_user.username = params[:comment_user][:username]
     @comment_user.password = params[:comment_user][:password]
     @comment_user.save
  
     if @comment_user.username.blank? || @comment_user.password.blank?
       redirect_to :back, notice: '用户名和密码不能为空'
       return
     end

     session[:current_comment_user] = @comment_user
     redirect_to article_path(params[:article_id])
   end

   def  logout
     session[:current_comment_user] = nil
     session[:is_comment_user_username] = '尚未登录'

     redirect_to article_path(params[:article_id])
   end
 end

# app/models/comment_user.rb

class CommentUser < ActiveRecord::Base
   has_many :comments
   has_many :articles, through: :comments
 end

class Comment < ActiveRecord::Base
   belongs_to :article
   belongs_to :comment_user
 end             

class Article < ActiveRecord::Base
   has_many :comments
   has_many :comment_users, through: :comments
 end

# config/routes.rb

Rails.application.routes.draw do

resources :comment_users do
    collection do
       delete :logout
     end
   end
 end

<p>注册评论用户</p>
     <%= form_for @comment_user, url: comment_users_path(article_id: params[:article_id]) do |f| %>
         <div>
           用户名: <%= f.text_field :username %>
           <p></p>
         </div>

         <div>
           密码: <%= f.password_field :password %>
           <p></p>
         </div>

         <div>
           <%= f.hidden_field :article_id, value: params[:article_id] %>
         </div>

         <div>
            <%= f.submit '注册' %>
         </div>
     <% end %>

 def show                                                                                           

     @comments = Comment.where('article_id = ?', params[:id]).all

end

 <div class='comment'>
     <% if session[:current_comment_user].present? %>                                                 
       欢迎您: <%= session[:current_comment_user]['username']%>
       <%= link_to '退出', logout_comment_users_path(article_id: params[:id]), method: :delete %></br>
     <% end %>
     <% if session[:current_comment_user].present? %>
       <%= form_tag "/comments", method: 'post' do %>
         <input type='hidden' name='comment_user_id' value='<%= params[:comment_user_id] %>' />       
         <input type='hidden' name='article_id' value='<%= params[:id] %>' />                         
         <p>正文:
         <%= text_field_tag "content" %>
         <%= submit_tag "提交", style:' margin-left: 5px;' %>
         </p>
       <% end %>
     <% else %>
       <p>
         <%= link_to '发表评论', new_comment_user_path(article_id: params[:id]) %>
       </p>
       <p>请先点击发表评论，登录后再进行评论。</p>
     <% end %>

     <p style='font-weight: bold;'>评论列表: </p>
     <% @comments.each do |comment| %>
         <p>姓名: <%= comment.comment_user.try(:username)%></p>
         <p>评论正文: <%= comment.content %></p>
     <% end %>
   </div>
 </div>