Josemar Furegatti de Abreu Silva: RAILS Using Scaffold to create CRUD application on PostgreSQL

1. Introduction

This post shows how to create a simple application using scaffolding generator connectiong to PostgreSQL.

2. Step-by-Step

2.1. Create application named 'weblog' using 'PostgreSQL' database

$ pwd
/home/rails-home
$ rails new weblog -d postgresql
$ cd weblog
$ pwd
/home/rails-home/weblog

2.2. Generate scaffold CRUD for 'post' entity with attributes title:string and body:string

a. Generate scaffold

$ rails generate scaffold post title:string body:text
Running via Spring preloader in process 2854
invoke active_record
create db/migrate/20170318144830_create_posts.rb
create app/models/post.rb
: :
invoke resource_route
route resources :posts
invoke scaffold_controller
create app/controllers/posts_controller.rb
invoke erb
create app/views/posts
create app/views/posts/index.html.erb
create app/views/posts/edit.html.erb
create app/views/posts/show.html.erb
create app/views/posts/new.html.erb
create app/views/posts/_form.html.erb
: :
invoke jbuilder
create app/views/posts/index.json.jbuilder
create app/views/posts/show.json.jbuilder
create app/views/posts/_post.json.jbuilder
: :

b. Checking what scaffold has done:

(i) migration script

$ cat db/migrate/*_create_posts.rb
class CreatePosts < ActiveRecord::Migration[5.0]
def change
create_table :posts do |t|
t.string :title
t.text :body
t.timestamps
end
end
end

(ii) model for application

$ cat app/models/post.rb
class Post < ApplicationRecord
end

(iii) controller with actions new, create, ..., destroy

$ cat app/controllers/posts_controller.rb
class PostsController < ApplicationController
before_action :set_post, only: [:show, :edit, :update, :destroy]
:
def index
:
end
:
def show
:
end
:
def new
:
end
:
def edit
:
end
:
def create
:
end
:
def update
:
end
:
def destroy
:
end
:
private
def set_post
:
end
:
def post_params
:
end
:
end

(iv) views

$ ls -la app/views/posts
total 36
drwxr-xr-x. 2 root root 4096 Mar 18 11:48 .
drwxr-xr-x. 4 root root 32 Mar 18 11:48 ..
-rw-r--r--. 1 root root 123 Mar 18 11:48 edit.html.erb
-rw-r--r--. 1 root root 579 Mar 18 11:48 _form.html.erb
-rw-r--r--. 1 root root 591 Mar 18 11:48 index.html.erb
-rw-r--r--. 1 root root 53 Mar 18 11:48 index.json.jbuilder
-rw-r--r--. 1 root root 88 Mar 18 11:48 new.html.erb
-rw-r--r--. 1 root root 104 Mar 18 11:48 _post.json.jbuilder
-rw-r--r--. 1 root root 227 Mar 18 11:48 show.html.erb
-rw-r--r--. 1 root root 40 Mar 18 11:48 show.json.jbuilder

c. Start RAILS server and observe what scaffold does for us

i) Configure RAILS on to listen for all interfaces

$ vim ./config/boot.rb
:
super.merge(Host: '0.0.0.0', Port: 3000)
:

ii) Create databases DEV and PROD using

$ rake db:create

iii) Create database tables using migrate

$ rails db:migrate

iv) Run rails server

$ rails server

v) Check results

http://localhost:3000 - See Yay! You're on Rails!
http://localhost:3000/posts - Simple CRUD application for Posts, you can do: new, show, edit, destroy
http://localhost:3000/posts.json - JSON object representing all posts: [{"id":1,"title":"1","body":"first","created_at":"2017-03-18T15:15:30.015Z","updated_at":"2017-03-18T15:16:05.960Z","url":"http://localhost:3000/posts/1.json"}]

2.3. Adding some validation

Edit model and add validation rule

$ vim app/models/post.rb

class Post < ApplicationRecord

validates_presence_of :title

end

Try to create a post without title and observe error validation: 1 error prohibited this post from being saved: Title can't be blank

2.3. Creating Comment model reference Post (master detail)

a. Create resource comment referencing post

$ rails generate resource comment post:references body:text
Running via Spring preloader in process 3025
invoke active_record
create db/migrate/20170318185201_create_comments.rb
create app/models/comment.rb
invoke test_unit
create test/models/comment_test.rb
create test/fixtures/comments.yml
invoke controller
create app/controllers/comments_controller.rb
invoke erb
create app/views/comments
invoke test_unit
create test/controllers/comments_controller_test.rb
invoke helper
create app/helpers/comments_helper.rb
invoke test_unit
invoke assets
invoke coffee
create app/assets/javascripts/comments.coffee
invoke scss
create app/assets/stylesheets/comments.scss
invoke resource_route
route resources :comments

b. Run migrate to create database table for 'comment'

$ rails db:migrate
== 20170318185201 CreateComments: migrating ===================================
-- create_table(:comments)
-> 0.1987s
== 20170318185201 CreateComments: migrated (0.1988s) ==========================

c. Configure nesting of routes on post controller to comment'

$ vim config/routes.rb

Rails.application.routes.draw do

resources :posts do

resources :comments

end

d. Check routes created

$ rails routes

Prefix Verb URI Pattern Controller#Action
post_comments GET /posts/:post_id/comments(.:format) comments#index
POST /posts/:post_id/comments(.:format) comments#create
new_post_comment GET /posts/:post_id/comments/new(.:format) comments#new
edit_post_comment GET /posts/:post_id/comments/:id/edit(.:format) comments#edit
post_comment GET /posts/:post_id/comments/:id(.:format) comments#show
PATCH /posts/:post_id/comments/:id(.:format) comments#update
PUT /posts/:post_id/comments/:id(.:format) comments#update
DELETE /posts/:post_id/comments/:id(.:format) comments#destroy
posts GET /posts(.:format) posts#index
POST /posts(.:format) posts#create
new_post GET /posts/new(.:format) posts#new
edit_post GET /posts/:id/edit(.:format) posts#edit
post GET /posts/:id(.:format) posts#show
PATCH /posts/:id(.:format) posts#update
PUT /posts/:id(.:format) posts#update
DELETE /posts/:id(.:format) posts#destroy

e. Check model 'comment' created

$ cat app/models/comment.rb

class Comment < ApplicationRecord

belongs_to :post

end

f. Adjust 'post' model to has many of 'comment' models

$ vim app/models/post.rb

class Post < ApplicationRecord

has_many :comments

validates_presence_of :title

end

2.4. Edit view of 'post' to show related 'comments'

a. Edit view 'show' of 'post' - add code to show related comments

$ vim app/views/posts/show.html.erb

:
<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>
<br><br>
<h2>Comments</h2>
<div id="comments">
<%# Expands to render partial: 'comments/comment', collection: @post.comments %>
<%= render @post.comments %>
</div>
<%= render 'comments/new', post: @post %>
</div>

b. Edit view templates '_form' and '_new' of 'Comment'

$ vim app/views/comments/_new.html.erb
<%= form_for([ @post, Comment.new ], remote: true) do |form| %>
Your comment:<br>
<%= form.text_area :body, size: '50x20' %><br>
<%= form.submit %>
<% end %>

$ vim app/views/comments/_comment.html.erb

c. Implement 'comment' controller actions

$ vim app/controllers/comments_controller.rb
class CommentsController < ApplicationController
before_action :set_post

def create
@post.comments.create! comments_params
redirect_to @post
end

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

def comments_params
params.required(:comment).permit(:body)
end

end

Josemar Furegatti de Abreu Silva

sábado, 18 de março de 2017

RAILS Using Scaffold to create CRUD application on PostgreSQL