MySQL と Ruby on Rails を使ったシンプルなブログ管理システムの開発方法

rails new blog
cd blog

default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: your_username
  password: your_password
  host: localhost

development:
  <<: *default
  database: blog_development

test:
  <<: *default
  database: blog_test

production:
  <<: *default
  database: blog_production
  username: blog
  password: <%= ENV['BLOG_DATABASE_PASSWORD'] %>

rails db:create

rails generate model Post title:string content:text
rails db:migrate

rails generate controller Posts

class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  def index
    @posts = Post.all
  end

  def show
  end

  def new
    @post = Post.new
  end

  def edit
  end

  def create
    @post = Post.new(post_params)

    if @post.save
      redirect_to @post, notice: 'Post was successfully created.'
    else
      render :new
    end
  end

  def update
    if @post.update(post_params)
      redirect_to @post, notice: 'Post was successfully updated.'
    else
      render :edit
    end
  end

  def destroy
    @post.destroy
    redirect_to posts_url, notice: 'Post was successfully destroyed.'
  end

  private

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

  def post_params
    params.require(:post).permit(:title, :content)
  end
end

<h1>Posts</h1>

<% @posts.each do |post| %>
  <h2><%= link_to post.title, post %></h2>
  <p><%= post.content %></p>
<% end %>

<p><%= link_to 'New Post', new_post_path %></p>

<h1><%= @post.title %></h1>
<p><%= @post.content %></p>

<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>

<h1>New Post</h1>

<%= render 'form' %>

<%= link_to 'Back', posts_path %>

<h1>Editing Post</h1>

<%= render 'form' %>

<%= link_to 'Show', @post %> |
<%= link_to 'Back', posts_path %>

<%= form_with(model: post, local: true) do |form| %>
  <% if post.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(post.errors.count, "error") %> prohibited this post from being saved:</h2>

      <ul>
        <% post.errors.full_messages.each do |message| %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :title %>
    <%= form.text_field :title %>
  </div>

  <div class="field">
    <%= form.label :content %>
    <%= form.text_area :content %>
  </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

rails server