Rails

new rails project


rails new <project_name>

start rails server


rails s

routing

in config/routes.rb


Rails.application.routes.draw do
    # root route is special
    root 'articles#index'

    # non-root route like this
    # trigger `index` action in `articles` when GET request on `articles`
    get 'articles', to: 'articles#index'
    
    # route with variable use `:`
    # the variable is passed to controller in the hash `params`
    # in this case `params[:id]`
    get 'articles/:id', to: 'articles#show'

end


Rails.application.routes.draw do
    resources :articles
end

this map route

URI pattern	controller#action
articles	articles#index
articles/new	articles#new
articles/:id	articles#show
(POST) articles	articles#create
articles/:id/edit	articles#edit
(PATCH) article/:id	articles#update
(DELETE) article/:id	articles#destroy

and set up URL and path helper method

method	return
article_path	“articles/#{article.id}”

model

in app/models

singular name

generate model

generate model Article with two field


rails g model Article title:string body:text

also generate database migration

generate and save new model object


# generate new article object
article = Article.new(title: 'Example', body: 'Example text.')

# save to database
article.save # => true

update model object


article.update # => true

validation of model object when save or update


# declare a `article_params` method to validate
def article_params
    params.require(:article).permit(:title, :author, :body, :status)
end

# use the method when try saving or updating
if @article.update(article_params)
    redirect_to @article
else
    render :edit, status: :unprocessable_entity
end

query model object from database


# query article by id
Article.find(1) # => 1 Article object or Nil

# query all articles
Article.all # => 1 ActiveRecord::Relation object

view

in app/views

`html.erb` file

embedded Ruby in HTML

run ruby code
```
<% … %>
```
run ruby code and render the return value
```
<%= … %>
```
write comment that does not render in result
```
<%# comment %>
```

access instance variable in view


<ul>
    <% @articles.each do |article| %>
        <li>
            <%= article.title %>
        </li>
    <% end %>
</ul>

link to other page in view

product a link with some_text to article_path
```
<%= link_to some_text, article %>
```
redirect to show a model object
```
redirect_to @article
```
- the browser make a new request
- use redirect_to to mutate database
render image
```
<%= image_tag image_path %>
```

link to the same page with different params


<%= link_to some_text,
  url_for(params.permit!.merge(field_to_change: field_value)) %>

partial template

partial has name starting with _

e.g.

_form.html.erb

access partial template from another view


<%= render 'comments/form' %>

relative path without _

add argument


render 'form', article: @article

# or the longer format
render partial: 'form', locals: { article: @article }

# or even longer format
render partial: 'form', object: @article, as: 'article'

render a collection


render @products

# or longer format
render partial: 'product', collection: @products

or even longer format


<% @products.each do |product| %>
    <%= render partial: "product", locals: { product: product } %>
<% end %>

controller

in app/controllers

controller for articles is articles_controller.rb

plural name

generate controller

generate ArticlesController and its index action


rails g controller Articles index

by default, index action of Articles render app/views/articles/index.html.erb

instance variable in controller

instance variable in controller can be accessed in view


# this will be accessed in `articles/index.html.erb`
    def index
        @article = Article.all
    end

controller method for resourceful routing

`index` method in controller

`show` method in controller

need to query model object by params[:id]

`new` method in controller

only initialize new model object

`create` method in controller

assign value to new model object and attempt to save it


def create
    @article = Article.new(title: '…', body: '…')
    if @article.save
        redirect_to @article
    else
        render :new, status: :unprocessable_entity
end

strong parameter

database

SQLite3 by default

migration

in db/migrate


rails db:migrate

console

open a rails irb console


rails console

Hotwire

Turbo

Turbo events

Steven Hé (Sīchàng)