Rails 3 Beginner to Builder 2011 Week 3

Beginner to Builder
Week 3
Richard Schneeman
@schneems

June, 2011
Friday, June 24, 2011

Austin on Rails
• Tuesday, 27th 7:00pm
• 7th and Brazos 8th Floor
• @austinonrails

@Schneems

Rails - Week 3
• Ruby
• Variables
• Rails
• JS/CSS/images
• Controllers
• Controller Testing
• Database Associations
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Variables
foobar # local variable

@foobar # instance variable, starts with @

@@foobar # class variable, starts with @@

$foobar # global variable, starts with $

FOOBAR # Constant, starts with a capitol letter

FooBar # Classes are constants

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Instance Variables

@color = "blue" color = "pink"
def instance_fur_color def local_fur_color
return @color return color
end end
puts instance_fur_color puts local_fur_color
>> "blue" >> NameError:
undefined local variable

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Instance Variables

@color = "blue" color = "pink"
def instance_fur_color def local_fur_color
return @color return defined?(color)
end end
puts instance_fur_color >> False
>> "blue"

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Instance Variables
class Dog
def set_color(color)
@fur_color = color
end
def color
"fur color is #{@fur_color}"
end
end
# create a Dog instance
lassie = Dog.new
# set color
lassie.set_color("brown")
# get @fur_color
lassie.color
>> "@fur_color is brown"
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Bad Scope
class Circle
$sides = 0
def self.sides
$sides
end
Triangle.sides
end
>> 3
Circle.sides
class Triangle
>> 3
$sides = 3
def self.sides
$sides
end
end

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Rails - Week 3
• Rails - A Place for Everything
• Public
• Images
• Javascripts
• Stylesheets

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Rails - Week 3
• Rails - A Place for Everything
• View Helpers
• <%= stylesheet_link_tag :all %>
• <%= javascript_include_tag :defaults %>
• Require Speciﬁc Files
• <%= image_tag ‘rails.png’ %>
• <%= stylesheet_link_tag ‘scaffold.css’ %>
• <%= javascript_include_tag ‘rails.js’ %>

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Controllers
• The C in MVC
• handles buisness logic
htt://localhost:3000/clients/new

class ClientsController < ApplicationController
def new
end
end

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Controllers
• Pass data to controllers via query
string

htt://localhost:3000/clients?status=activated
?status=activated

?status=activated&level=23

?status=deactivated&level=1&foo=bar

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Controllers
• params, get data from the url
• instance variables pass data to
view
http://localhost:3000/clients?status=activated
def index
@status = params[:status]
if @status == "activated"
@clients = Client.activated
else
@clients = Client.unactivated
end
end
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Controllers
• Receive Arrays
Arrays

GET /clients?ids[]=1&ids[]=2&ids[]=3
params[:ids] # => [“1”,”2”,”3”]

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Controllers
Form
• Receive Hashes from forms
<form action="/clients" method="post">
<input type="text" name="client[name]" value="Acme" />
<input type="text" name="client[phone]" value="12345" />
<input type="text" name="client[address][postcode]" value="12345" />
</form>

Hash
params[:client] # =>
{:name => “Acme”,
:phone => “12345”,
:address => {:postcode => “12345”}
}
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Controllers
• Control application ﬂow
• render content
htt://localhost:3000/clients/new
# send to another action/url
redirect_to "/home"

# render content
render :action => "new"
render :layout => "awesome"
render :text => "foo"
render :json => {}
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Rails - Week 3
• Functional Testing - Controllers
• web request successful?

• user redirected to the right page?

• user successfully authenticated?

• correct object stored in the template?

• appropriate message displayed to the user ?

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Rails - Week 3
• Use HTTP to send data to controller
• get, post, put, head, delete

• Verify Response
• Assigns
• Cookies
• Flash
• Session

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Cookies?
• Stored on the user’s computer
• Mostly used for settings

cookies["remember_me"] = true

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Session?
• store and access user speciﬁc data
• Uses cookies to store data by default
• very quick, and secure
• NOT for critical information
• Put it in the database
session[:logged_in] = true
session[:user_id] = 57
session[:is_mobile] = false
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Flash?
• Part of the session
• cleared after each request
• useful for error messages

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Flash?
flash[:notice] = "You must sign in to see this page."

or

redirect_to signup_url,
:notice => "You must sign in to see this page."

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Rails - Week 3
• Functional Testing - Controllers
• Send data to controller
• Verify response
class PetControllerTest < ActionController::TestCase
test "should get index" do
get :index
assert_response :success
end
end

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Rails - Week 3
• Use HTTP to send data
• Get, Post, Put, Delete
Controller
• assigns(:post) = @post
def create
@post = Post.create(params[:post])
end

Test

post :create, :post => { :title => 'Some title'}
assert assigns(:post).is_a?(Post)

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Rails - Week 3
• Assert diﬀerence

assert_difference('Post.count', 1) do
post :create, :post => { :title => 'Some title'}
end

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Rails - Week 3

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Associations
• Relational Databases
• Primary Key
• unique key can identify
each row in a table
• Foreign Key
• Relates a row keyanother
row’s primary
to

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Primary Key
• Unique identiﬁer for all objects

Hats:
id: 557
style: "Fedora"

Hats:
id: 687
style: "Cowboy"

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Foreign Key
• Relates to another row’s primary key

Hats
id: 557
style: "Fedora"
inspector_id: 35

Inspectors
id: 35
name: "John"

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Foreign Key
• Creates relationships
Inspectors
id: 35
name: "John"

Hats Hats Hats
id: 557 id: 558 id: 559
style: "Fedora" style: "Ballcap" style: "Silly"
inspector_id: 35 inspector_id: 35 inspector_id: 35

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Belongs_To
• belongs_to :parent_class
• Sets Foreign Key

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Has_Many
• has_many :child_class
• Builds Association in Ruby

i.e. Hat inspector has many hats
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Has_Many
• How Does this Help?
• Related objects contain links to one
another
• Get one object, you’ve got all associated
>> myCustomer = Customer.where(:id => 2)
>> orders = myCustomer.orders.all

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Has_Many
• Caveats
• myCustomer.orders builds SQL and hits the database

• N+1 Problem - Imagine
• You query 100 customers
• Each Customer has 100 orders
• Each Order has 100 products
• ...
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Associations
• N+1 - How do we Fix it?
• What if we could Pre-load Associations?
• Includes
Customer.includes(:orders => :products).all

This would generate 1 database query!!
Will take signiﬁcantly less time than alternative
Note: database access is almost always be your bottleneck

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Has_Many :Through =>
• Chain Associations Using :Through

What Classes have foreign keys?

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• Appointments
• physician_id
• patient_id

What Classes have foreign keys?

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• Physician Class
• Uses Appointments
• Finds Patients
• Automatically

>> dr = Physicians.first
>> dr.patients

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Has & Belongs To Many
• HABTM (has and belongs to many)
• Creates direct many to many relationship

This is essentially using :through with a
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single purpose table: assemblies_parts

HABTM - Vs. :Through
• Use HABTM
• Don’t need to do anything with the relationship
model
• Restricted DB size
• Use :through
• Need validations
• Need callbacks
• Need extra attributes
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Questions?
http://guides.rubyonrails.org
http://stackoverﬂow.com

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Rails 3 Beginner to Builder 2011 Week 3

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