Layouts and Rendering in Rails, Season 2

Ror lab. season 2
- the 12th round -

Layouts and Rendering

December 15th, 2012

Hyoseong Choi

Contents

• Rendering methods
• Layouts with multiple content sections
• DRY using partial templates
• Nested layouts( or sub-templates)

Fit Together
Request

ro
ut
er
hea
Controller
vy ng
cod deri
es ren
layout partial

Model View

DB Response

Creating Response

• Three HTTP responses by Controller
➡ call “render” : full response
➡ call “redirect_to” : redirect status code
➡ call “head” : HTTP headers

Default Rendering
Controllers automatically render

• views with names corresponding to valid
routes.
• {action_name}.html.erb

Default Rendering
/books

class BooksController < ApplicationController
end
BooksController

resources :books
conﬁg/routes.rb

<h1>Books are coming soon!</h1>
app/views/books/index.html.erb

Default Rendering
resources :books
conﬁg/routes.rb

$ rake routes CONTROLLER=books

books GET /books(.:format) books#index
POST /books(.:format) books#create
new_book GET /books/new(.:format) books#new
edit_book GET /books/:id/edit(.:format) books#edit
book GET /books/:id(.:format) books#show
PUT /books/:id(.:format) books#update
DELETE /books/:id(.:format) books#destroy

Default Rendering
  def index
    @books = Book.all
  end
end

• {action_name}.html.erb
C oC : app/views/books/index.html.erb

Default Rendering
• app/views/books/index.html.erb
<h1>Listing Books</h1>

<table>
  <tr>
    <th>Title</th>
    <th>Summary</th>
    <th></th>
    <th></th>
    <th></th>
  </tr>

<% @books.each do |book| %>
  <tr>
    <td><%= book.title %></td>
    <td><%= book.content %></td>
    <td><%= link_to 'Show', book %></td>
    <td><%= link_to 'Edit', edit_book_path(book) %></td>
    <td><%= link_to 'Remove', book,
:confirm => 'Are you sure?',
:method => :delete %></td>
  </tr>
<% end %>
</table>

<br />

<%= link_to 'New book', new_book_path %

Using ‘Render’
Many ways to customize rendering
• Default view
: for a Rails template / a speciﬁc template / a ﬁle / inline code /
nothing
• text / JSON / XML

  def index
    @books = Book.all
render “index”
render_to_string “index”
render :nothing => true
  end
end

Using ‘Render’
Rendering an Action’s view

def update
  @book = Book.find(params[:id])
  if @book.update_attributes(params[:book])
    redirect_to(@book)
  else
    render "edit"
  end
as a String
end

Using ‘Render’

def update
    redirect_to(@book)
  else
    render :edit
  end
as a Symbol
end

Using ‘Render’

def update
    redirect_to(@book)
  else
    render :action => "edit"
  end
to render “edit” action’s view
end

Using ‘Render’
Rendering an Action’s Template
from Another Controller

def update
    redirect_to(@book)
  else
    render "products/show"
    render :template => "products/show"
  end
from another controller
end

Using ‘Render’
Rendering an Arbitrary File

def update
    redirect_to(@book)
  else
render "/u/apps/warehouse_app/current/app/
views/products/show"
    render :file => "/u/apps/warehouse_app/current/
app/views/products/show", :layout => true
  end
end

Using ‘Render’
Wrapping it up

render :edit
render :action => :edit
render 'edit'
render 'edit.html.erb'
render :action => 'edit'
render :action => 'edit.html.erb'
render 'books/edit'
render 'books/edit.html.erb'
render :template => 'books/edit'
render :template => 'books/edit.html.erb'
render '/path/to/rails/app/views/books/edit'
render '/path/to/rails/app/views/books/edit.html.erb'
render :file => '/path/to/rails/app/views/books/edit'
render :file => '/path/to/rails/app/views/books/
edit.html.erb'

Using ‘Render’
with :inline
default type :ERB

render :inline =>
"<% products.each do |p| %><p><%= p.name %></p><% end
%>"

render :inline =>
"xml.p {'Horrid coding practice!'}", :type => :builder

Using ‘Render’
with :text

render :text => "OK", :layout => true

short response to AJAX
or web service requests

Using ‘Render’
with :json

render :json => @product

built-in support for JSON

Using ‘Render’
with :xml

render :xml => @product

built-in support for XML

Using ‘Render’
with :js

render :js => "alert('Hello Rails');"

built-in support for XML

Options
for Render
• :content_type
• :layout
• :status
• :location

Options
for Render
:content_type option

render :file => filename, :content_type => 'application/rss'

Default MIME type
:html - text/html
:json - application/json
:xml - application/xml

Options
for Render
:layout option

render :layout => 'special_layout'

to tell Rails to use a specific file
as the layout for the current action

render :layout => false

Options
for Render
:location option

render :xml => photo, :location => photo_url(photo)

to set the HTTP Location header

Options
for Render
:status option

render :status => 500
render :status => :forbidden

http://www.codyfauser.com/2008/7/4/rails-http-status-code-to-symbol-mapping

Status Code Status Message Symbol Status Code Status Message Symbol
1xx Informational 406 Not Acceptable :not_acceptable
100 Continue :continue Proxy Authentication :proxy_authentication_req
407
101 Switching Protocols :switching_protocols Required uired
408 Request Timeout :request_timeout
102 Processing :processing
409 Conflict :conflict
2xx Success 410 Gone :gone
200 OK :ok 411 Length Required :length_required
201 Created :created
412 Precondition Failed :precondition_failed
202 Accepted :accepted
413 Request Entity Too Large :request_entity_too_large
203 Non-Authoritative :non_authoritative_inform
Information ation 414 Request-URI Too Long :request_uri_too_long
204 No Content :no_content
205 Reset Content :reset_content 415 Unsupported Media Type :unsupported_media_type
206 Partial Content :partial_content 416 Requested Range Not :requested_range_not_sati
207 Multi-Status :multi_status Satisfiable sfiable
417 Expectation Failed :expectation_failed
226 IM Used :im_used
422 Unprocessable Entity :unprocessable_entity

423 Locked :locked
3xx Redirection
300 Multiple Choices :multiple_choices 424 Failed Dependency :failed_dependency
301 Moved Permanently :moved_permanently 426 Upgrade Required :upgrade_required
302 Found :found
303 See Other :see_other
5xx Server Error
304 Not Modified :not_modified
500 Internal Server Error :internal_server_error
305 Use Proxy :use_proxy
307 Temporary Redirect :temporary_redirect 501 Not Implemented :not_implemented
4xx Client Error 502 Bad Gateway :bad_gateway
400 Bad Request :bad_request 503 Service Unavailable :service_unavailable
401 Unauthorized :unauthorized
504 Gateway Timeout :gateway_timeout
402 Payment Required :payment_required
505 HTTP Version Not :http_version_not_support
403 Forbidden :forbidden Supported ed
404 Not Found :not_found 507 Insufficient Storage :insufficient_storage

405 Method Not Allowed :method_not_allowed 510 Not Extended :not_extended

Finding Layouts
• Rails first looks for a file in app/views/layouts
with the same base name as the controller.

Current
Controller layout
layout

inheritance

Application layout

Finding Layouts
Specifying Layouts for Controllers

class ProductsController < ApplicationController
  layout "inventory"
  #...
end
app/views/layouts/inventory.html.erb

class ApplicationController < ActionController::Base
  layout "main"
  #...
end
app/views/layouts/main.html.erb

Finding Layouts
Choosing Layouts at Runtime

  layout :products_layout

  def show
    @product = Product.find(params[:id])
  end

  private
    def products_layout
      @current_user.special? ? "special" : "products"
    end

end

Finding Layouts
Choosing Layouts at Runtime

layout Proc.new { |controller|
controller.request.xhr? ? 'popup' : 'application' }
end
using inline method!

Finding Layouts
Conditional Layouts

layout "product", :only => [:index, :rss]
end

layout "product", :except => [:index, :rss]
end

Finding Layouts
Layout Inheritance (1) cascading downward

‣ application_controller.rb
class ApplicationController < ActionController::Base
layout "main"
end

‣ posts_controller.rb
class PostsController < ApplicationController
end

Finding Layouts
Layout Inheritance (2) cascading downward

‣ special_posts_controller.rb
class SpecialPostsController < PostsController
layout "special"
end

Finding Layouts
cascading downward

Layout Inheritance (3)
‣ old_posts_controller.rb
class OldPostsController < SpecialPostsController
  layout false

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

  def index
    @old_posts = Post.older
    render :layout => "old"
  end
  # ...
end

Using Redirect_to
• redirect_to
- tell the browser to send a new request
for a different URL
• cf. render
- a view template

redirect_to photos_url
redirect_to :back

Using Redirect_to s : 30
2
tatu
lt s
de fau

Different Redirect Status Code

redirect_to photos_path, :status => 301

Using Redirect_to
Render vs Redirect_to

def index def index
  @books = Book.all   @books = Book.all
end end

def show def show
  @book = Book.find_by_id(params[:id])   @book = Book.find_by_id(params[:id])
  if @book.nil?   if @book.nil?
    render :action => "index"     redirect_to :action => :index
  end   end
end end

a round trip to the browser

Using Redirect_to
Render vs Redirect_to

def index
  @books = Book.all
end

def show
  @book = Book.find_by_id(params[:id])
  if @book.nil?
    @books = Book.all
    render "index", :alert => 'Your book was not found!'
  end
end

one stop rendering

Head-Only
Responses

• render :nothing
• a more obvious alternative
‘head’ method

Head-Only
Responses
head :bad_request

HTTP/1.1 400 Bad Request
Connection: close
Date: Sun, 24 Jan 2010 12:15:53 GMT
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
X-Runtime: 0.013483
Set-Cookie: _blog_session=...snip...; path=/; HttpOnly
Cache-Control: no-cache

Head-Only
Responses
head :created, :location => photo_path(@photo)

HTTP/1.1 201 Created
Connection: close
Date: Sun, 24 Jan 2010 12:16:44 GMT
Transfer-Encoding: chunked
Location: /photos/1
Content-Type: text/html; charset=utf-8
X-Runtime: 0.083496
Set-Cookie: _blog_session=...snip...; path=/; HttpOnly
Cache-Control: no-cache

Structuring
Layouts
Three tools for knitting fragmented outputs

• Asset tags ( for asset links )
• yield and content_for ( for layouts )
• Partials ( for refactoring )

Structuring
Layouts
Asset Tag Helpers

• auto_discovery_link_tag
• javascript_include_tag in <head> section

• stylesheet_link_tag
• image_tag
• video_tag in <body> section

• audio_tag

Structuring
Layouts
Asset Tag Helpers

auto_discovery_link_tag RSS or ATOM feeds

<%= auto_discovery_link_tag(:rss, {:action => "feed"},
{:title => "RSS Feed"}) %>

Structuring
Layouts
Asset Tag Helpers

javascript_include_tag

<%= javascript_include_tag "main" %>

<script src='/assets/main.js' type="text/javascript"></script>

• app/assets/javascripts
• lib/assets/javascripts
• vendor/assets/javascripts


<%= javascript_include_tag "main", "columns" %>

<%= javascript_include_tag "main", "/photos/columns" %>

<%= javascript_include_tag "http://example.com/main.js" %>

<%= javascript_include_tag :defaults %> without asset pipeline

<%= javascript_include_tag :all %> without asset pipeline

Disable
Asset Pipeline

• conﬁg/application.rb
# Enable the asset pipeline
conﬁg.assets.enabled = true


<%= javascript_include_tag :defaults %> without asset pipeline

<script src="/javascripts/jquery.js" type="text/javascript"></script>
<script src="/javascripts/jquery_ujs.js" type="text/javascript"></script>

public/javascripts

with asset pipeline without asset pipeline
• app/assets • public/javascripts
• lib/assets
• vendor/assets

javascript_include_tag :defaults

:defaults expansion in config/application.rb

config.action_view.javascript_expansions[:defaults]
= %w(foo.js bar.js)

new defaults expansion in config/application.rb

config.action_view.javascript_expansions[:projects]
= %w(projects.js tickets.js)

public/javascripts/application.js with :default

javascript_include_tag :all

public/javascripts/*.*

<%= javascript_include_tag :all, :recursive => true %>

combining multiple files into a single download

<%= javascript_include_tag "main", "columns", :cache => true %>

public/javascripts/all.js

<%= javascript_include_tag "main", "columns",
:cache => 'cache/main/display' %

location of cache

stylesheet_link_tag

assets/stylesheets/ with Asset Pipeline

<%= stylesheet_link_tag "main" %>

<%= stylesheet_link_tag "main", "columns" %>

<%= stylesheet_link_tag "main", "/photos/columns" %>

<%= stylesheet_link_tag "http://example.com/main.css" %>

stylesheet_link_tag :all

public/stylesheets/ without Asset Pipeline

<%= stylesheet_link_tag :all %>

<%= stylesheet_link_tag :all, :recursive => true %>

<%= stylesheet_link_tag "main", "columns", :cache => true %>

<%= stylesheet_link_tag "main", "columns",
:cache => 'cache/main/display' %>

image/video/audio
Asset pipeline - Asset pipeline +

• app/assets/
images/
videos/

• public/images
audios/

• public/videos • lib/assets/
images/
videos/
audios/

• public/audios
• vendor/assets/
images/
videos/
audios/

Yield
• a section where content from the view
should be inserted. content_for

<html> <html> named yield
  <head>   <head>
  </head>   <%= yield :head %>
  <body>   </head>
  <%= yield %>   <body>
  </body>   <%= yield %>
</html>   </body>
</html>

single yield multiple yields

content_for
<html>
  <head>
  <%= yield :head %>
  </head>
<%= yield :head %>   <body>
  <%= yield %>
  </body>
<% content_for :head do %> </html>
  <title>A simple page</title>
<% end %>
<html>
<p>Hello, Rails!</p>   <head>
  <title>A simple page</title>
  </head>
  <body>
  <p>Hello, Rails!</p>
  </body>
</html>

Partial
• breaking the render process into more
chunks
• moving the code chunk to its own ﬁle
• _partial.html.erb vs partial.html.erb
• to simplify views
• partial layout

Partial
<%= render "menu" %>

<%= render "shared/menu" %>

<%= render "shared/ad_banner" %>

<h1>Products</h1>

<p>Here are a few of our fine products:</p>
...

<%= render "shared/footer" %>

<%= render :partial => "link_area", :layout => "graybar"

Local Variables
<h1>New zone</h1>
<%= error_messages_for :zone %>
<%= render :partial => "form", :locals => { :zone =>
@zone } %>

<%= form_for(zone) do |f| %>
  <p>
    <b>Zone name</b><br />
    <%= f.text_field :name %>
  </p>
  <p>
    <%= f.submit %>
  </p>
<% end %>

A Partial variable
• a local variable with the same name as the
partial
• pass an object in to this local variable
<%= render :partial => "customer", :object => @new_customer %>

<%= render @customer %>

Rendering Collections
Rails determines the name of the partial to use by looking at
the model name in the collection. In fact, you can even create a
heterogeneous collection and render it this way

<h1>Products</h1>
<%= render :partial => "product",
:collection => @products %>
index.html.erb

<p>Product Name: <%= product.name %></p>
_product.html.erb

Rendering Collections
Rails determines the name of the partial to use by looking at
the model name in the collection. In fact, you can even create a
heterogeneous collection and render it this way

ra
ils
3.
<h1>Products</h1> 0
<%= render(@products) || ‘there are no products
available.’ %>
index.html.erb

<p>Product Name: <%= product.name %></p>
_product.html.erb

Heterogenous
Collections
<h1>Contacts</h1>
<%= render [customer1, employee1, customer2, employee2] %>
index.html.erb

<p>Customer: <%= customer.name %></p>
customers/_customer.html.erb

<p>Employee: <%= employee.name %></p>
employees/_employee.html.erb

Local Variables
render :partial => "product",
:collection => @products,
:as => :item %>

<%= render :partial => 'products',
:collection => @products,
:as => :item,
:locals => {:title => "Products Page"} %>

Spacer Templates

<%= render :partial => @products,
:spacer_template => "product_ruler" %>

Layouts

• Application Layout
• Controller Layout
• Action Layout
• Partial Layout

Layouts
layout view template
<html> <% content_for :head do %>
  <head>   <title>A simple page</
  <%= yield :head %> title>
  </head> <% end %>
  <body>
  <%= yield %> <p>Hello, Rails!</p>
  </body>
</html>
yield placeholder

yield(:head) content_for :head

yield(:bar) content_for :bar

Nested Layouts
NewsController Layout ApplicationController Layout
<% content_for :stylesheets do %>
<html>
  #top_menu {display: none}
<head>
  #right_menu {float: right; background-color:
  <title><%= @page_title or 'Page Title' %></
yellow; color: black}
title>
<% end %>
  <%= stylesheet_link_tag 'layout' %>
  <style type="text/css">
<% content_for :content do %>
<%= yield :stylesheets %>
  <div id="right_menu">Right menu items here</
</style>
div>
</head>
  <%= content_for?(:news_content)
<body>
? yield(:news_content)
  <div id="top_menu">Top menu items here</div>
: yield %>
  <div id="menu">Menu items here</div>
<% end %>
  <div id="content">
<%= content_for?(:content)
? yield(:content)
<%= render :template => 'layouts/application' %>
: yield %>
</div>
</body>
</html>

Layouts and Rendering in Rails, Season 2

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