Rails 3 Beginner to Builder 2011 Week 8

Beginner to Builder
Week8

July, 2011
Monday, August 8, 11

Rails - Week 8
• Dealing with nil
• Acceptance Testing
• Partials
• Cells
• Memcache

@Schneems

Dealing with Nil
user = User.where(:username => "schneems").first
#<User ... >
user.image_url
>> "/schneems.png"

user = nil
user.image_url
# NameError: undefined local variable or method `user'
for #<Object:0x1001dc288>

@Schneems

try to deal
# use try from ActiveSupport
user = User.where(:username => "schneems").first
#<User ... >
user.try(:image_url) || "/not_found.png"
>> "/schneems.png"

user = nil
user.try(:image_url) || "/not_found.png"
>> "/not_found.png"

@Schneems

|| & ||=
per_page = params[:per_page]
per_page = 10 if per_page.blank?

# instead
per_page = params[:per_page]||10

# or
per_page = params[:per_page]
per_page ||= 10

@Schneems

‘if’ returns result
# if returns to where it was called
result = if true
"foo"
else
"bar"
end

puts result
>> "foo"

result = if false
"foo"
else
"bar"
end

puts result
>> "bar"
@Schneems

Acceptance Testing
• Run your full application stack
• Behavior Driven Development (BDD)
• High payout for little time testing
• slow
• potentially brittle

@Schneems

Capybara & Rspec
• Capybara
• Headless browser
• open your webpages
• click links ...
Gemﬁle
gem 'capybara', '0.3.7'
gem 'rspec-rails', '1.3.2'

@Schneems

Capybara & Rspec
# go to a path
visit root_path
visit "/"

# click buttons
click "sign in"

# fill out forms
fill_in ‘Email’, :with => "schneems@example.com"

@Schneems

Capybara & Rspec
http://codingfrontier.com/integration-testing-setup-with-rspec-and-capy
/spec/acceptance/signin_spec.rb
context "as a guest on the sign in page" do
# Generate a valid user
let(:user) { Factory(:user) }
context ‘with valid credentials’ do
#Fill in the form with the user’s credentials and submit it.
before do
visit root_path
click ‘Sign In’
fill_in ‘Email’, :with => user.email
fill_in ‘Password’, :with => ‘password’
click ‘Submit’
end

it "has a sign out link" do
page.should have_xpath(‘//a’, :text => ‘Sign Out’)
end

it "knows who I am" do
page.should have_content(“Welcome, #{user.email}!”)
end
end
end
@Schneems

DRY Views
• Helpers
• Small resusable components
• content_for
• Control page ﬂow of compnents out of
normal
placement

• Partials
• Large reusable components
• Cells
• type logic is needed when controller
Reusable components
@Schneems

ViewHelpers
• Rails has build in helpers
• link_to
• image_tag
• etc.
• Write your Own

@Schneems

ViewHelpers
app/helpers/product_helper.rb
link_to_product(product = nil)
link_to image_tag(product.image_url),
product_path(product), :class => 'product'
end

app/views/product/index.html.erb
<%= link_to_product(@product) %>

<a href=“...” class=”product”>
<imgr src = “...” />
</a>
@Schneems

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

@Schneems

content_for in layouts
• use helpers & content_for together
in layouts

<body id="<%= id_for_body(yield(:body_id)) %>"
class="<%= classes_for_body(yield(:body_class)) %>
<%= logged_in? ? 'logged-in' : 'not-logged-in' %>">
<%= yield %>
</body>

@Schneems

content_for in layouts
# content_for head
<%= yield :head_analytics %>
<%= yield :head_stylesheets %>
<%= yield :head_scripts %>
<%= yield :head %>

# content_for body
<%= yield :main_title %>
<%= yield :sidebar_title %>
<%= yield :sidebar %>

# content_for footer
<%= yield :footer %>
<%= yield :footer_libraries %>
<%= yield :footer_scripts %>
<%= yield :footer_analytics %>

@Schneems

Partials
• Reusable chunks of view code
<%# renders 'spots.html.erb' with @spot %>
<%= render :partial => "spot", :object => @spot %>
<%= render "spot", :object => @spot %>
<%= render @spot %>

<%# renders 'spots.html.erb' for each spot in @spots %>
<%= render @spots %>
<%= render "spot", :collection => @spots %>

@Schneems

Partials

<%= render @spots %>

/spots/_spots.html.erb
<div>
<h3>Name:</h3>
<p><%= spot.name %></p>
<p><%= spot.description %></p>
</div>

@Schneems

Partials
• Locals
<%= render @spots, :locals => {:foo => ”bar”} %>

/spots/_spots.html.erb
<div>
<h3>Name:</h3>
<p><%= foo %></p>
</div>
@Schneems

Partials
• Optional Locals
<%# renders 'spot.html.erb' for each spot in @spots %>
<%= render @spot2 %>

/spots/_spot.html.erb
<div>
<h3>Name:</h3>
<p><%= local_assigns[:foo]||'something else' %></p>
</div>
@Schneems

Cells
• View Components
• Look and Feel like Controllers

gem install cells

@Schneems

Cells
/app/views/product/index.html
<div id="header">
<%= render_cell :cart, :display, :user => @current_user %>

/app/cells/cart_cell.rb
class CartCell < Cell::Rails
def display(options)
user = args[:user]
@items = user.items_in_cart
render # renders display.html.haml
end
end
/app/cells/cart.display.html.erb
<p>You have <%= @items.size %></p>
@Schneems

Caching
• Store data in alater so it can be
served quicker
cache

@Schneems

Page Caching
• Super Fast
• Limited use cases
class ProductsController < ActionController
caches_page :index

def index
@products = Products.all
end
end

http://guides.rubyonrails.org/caching_with_rails.html
@Schneems

Page Caching
caches_page :index

def index
@products = Products.all
end

def create
expire_page :action => :index
end
end

http://guides.rubyonrails.org/caching_with_rails.html
@Schneems

Action Caching
• Allows Authentication checks
before_filter :authenticate
caches_action :index

def index
@products = Product.all
end

def create
expire_action :action => :index
end
end
@Schneems

Action Caching
• :layout => false
• allows dynamic currentthe layout to
render such as
info in
user
• :if & :unless
•
caches_action :index, :layout => false
caches_action :index, :if => lambda {current_user.present?}
caches_action :index, :unless => lambda {current_user.blank?}

@Schneems

Fragment Caching
• Cache individual parts of pages
<% cache('all_available_products') do %>
All available products:
<% end %>

@Schneems

Fragment Caching
• Cache individual parts of pages
<% cache(:action => 'recent',
:action_suffix => 'all_products') do %>
All available products:
...
<%- end -%>

@Schneems

Fragment Caching
• Expire fragments
expire_fragment(:controller => 'products',
:action => 'recent',
:action_suffix => 'all_products')

@Schneems

Sweeping Cache
before_filter :authenticate
caches_action :index
cache_sweeper :product_sweeper

def index
@products = Product.all
end
end

@Schneems

Sweeping Cache
class ProductSweeper < ActionController::Caching::Sweeper
observe Product # This sweeper is going to keep an eye on the Product model
# If our sweeper detects that a Product was created call this
def after_create(product)
expire_cache_for(product)
end

private
def expire_cache_for(product)
# Expire the index page now that we added a new product
expire_page(:controller => 'products', :action => 'index')
expire_fragment('all_available_products')
end
end
@Schneems

Cache Stores
• Set the Cache store in your
environment

ActionController::Base.cache_store = :memory_store
ActionController::Base.cache_store = :drb_store,
"druby://localhost:9192"
ActionController::Base.cache_store = :mem_cache_store,
"localhost"

@Schneems

Cache Stores
• Simple Key/Value storage
Rails.cache.read("city") # => nil
Rails.cache.write("city", "Duckburgh")
Rails.cache.read("city") # => "Duckburgh"

@Schneems

Cache Stores
• fetch
Rails.cache.fetch("city") do
"Duckburgh"
end
# => "Duckburgh"

@Schneems

Cache Stores
• Expires_in
Rails.cache.write("city", "Duckburgh", :expires_in =>
1.minute)
sleep 120

@Schneems

Memcache
• Cache your rails objects
• Memcache Gem
• Key Value Store (NOSQL)
• Use to cache Expensive Queries
require 'memcached'
$cache = Memcached.new("localhost:11211")
$cache.set("foo", "bar")
$cache.get("foo")
=> "bar"

@Schneems

Memcache
# store strings
$cache.set("key", "value")
$cache.get("key")
=> "bar"

# store any ruby object
$cache.set("foo", [1,2,3,4,5])
$cache.get("foo")
=> [1,2,3,4,5]

# srsly any ruby object
$cache.set("foo", User.last)
$cache.get("foo")
=> #< User ... >
@Schneems

Memcache

ActionController::Base.cache_store = :mem_cache_store,
"localhost"

@Schneems

Memcache
• Cache frequent queries
class User < ActiveRecord::Base
def self.fetch(username)
Rails.cache.fetch("user:#{username}") do
User.where(:username => "#{username}").first
end
end
end

=> User.fetch("schneems") #=> #<User id: 263595 ... >

@Schneems

Memcache
• Cache expensive queries
def fetch_friends
Rails.cache.fetch("users:friends:#{self.id}") do
friends = Friendships.where(:user_1_id => self.id)
end
end
end

=> User.fetch("schneems").fetch_friend_ids

@Schneems

Memcache
• Blazing Fast
# Database
Benchmark.measure do
User.where(:username => "schneems").first
end.real
=> 0.09 s

# Memcache
Benchmark.measure do
User.fetch("schneems")
end.real
=> 0.0009 s
@Schneems

Memcache
• Key Value Store
• Holds ruby objects
• Extremely fast
• volatile
• available on Heroku
>> heroku addons:add memcache

@Schneems

Bonus - Keytar
• includeKeytar to generate Keys
Use Keytar
define_keys :username, :friends
•
end Use those keys in Memcache

User.username_key("schneems")
=> "user:username:schneems"
user = Rails.cache.fetch(User.username_key("schneems"))
=> # < User id:33 ... >

user.friends_key
=> "users:friends:33"
friends = Rails.cache.fetch(user.friends_key)
=> #[#< User ... >, #< User ... >, ... ]
@Schneems

Questions?
http://guides.rubyonrails.org
http://stackoverﬂow.com
http://peepcode.com

@Schneems

Rails 3 Beginner to Builder 2011 Week 8

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