Rails 3 Beginner to Builder 2011 Week 3

June, 2011

Beginner to BuilderWeek 3Richard Schneeman@schneems

Friday, June 24, 2011

@Schneems

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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Variablesfoobar # 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"

def instance_fur_color

return @color

end

puts instance_fur_color

>> "blue"

color = "pink"

def local_fur_color

return color

end

puts local_fur_color

>> NameError:

undefined local variable


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Instance Variables

@color = "blue"

def instance_fur_color

return @color

end

puts instance_fur_color

>> "blue"

color = "pink"

def local_fur_color

return defined?(color)

end

>> False


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class Dog def set_color(color) @fur_color = color end def color

"fur color is #{@fur_color}" endend# create a Dog instancelassie = Dog.new

# set colorlassie.set_color("brown")# get @fur_colorlassie.color>> "@fur_color is brown"

Instance Variables


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Bad Scopeclass Circle

$sides = 0

def self.sides

$sides

end

end

class Triangle

$sides = 3

def self.sides

$sides

end

end

Triangle.sides

>> 3

Circle.sides

>> 3


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Rails - Week 3• Rails - A Place for Everything

• Public

• Images

• Javascripts

• Stylesheets


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• 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’ %>

Rails - Week 3


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Controllers• The C in MVC

• handles buisness logic

class ClientsController < ApplicationController

def new

end

end

htt://localhost:3000/clients/new


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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

def index

@status = params[:status]

if @status == "activated"

@clients = Client.activated

else

@clients = Client.unactivated

end

end

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




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Controllers• Receive Arrays

GET /clients?ids[]=1&ids[]=2&ids[]=3

params[:ids] # => [“1”,”2”,”3”]

Arrays


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Controllers• 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”}

}

Form


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Controllers• Control application flow

• render content

# send to another action/url

redirect_to "/home"

# render content

render :action => "new"

render :layout => "awesome"

render :text => "foo"

render :json => {}

htt://localhost:3000/clients/new


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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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• Stored on the user’s computer

• Mostly used for settings

cookies["remember_me"] = true

Cookies?


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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."

redirect_to signup_url,

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

or


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class PetControllerTest < ActionController::TestCase

test "should get index" do

get :index

assert_response :success

end

end

• Functional Testing - Controllers

• Send data to controller

• Verify response

Rails - Week 3


• Use HTTP to send data

• Get, Post, Put, Delete

• assigns(:post) = @post

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post :create, :post => { :title => 'Some title'}

assert assigns(:post).is_a?(Post)

Rails - Week 3

def create

@post = Post.create(params[:post])

end

Controller

Test


• Assert difference

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Rails - Week 3

assert_difference('Post.count', 1) do

post :create, :post => { :title => 'Some title'}

end


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Rails - Week 3


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• Relational Databases

• Primary Key

• unique key can identify each row in a table

• Foreign Key

• Relates a row to another row’s primary key

Associations


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• Unique identifier for all objectsPrimary Key

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

id: 557

style: "Fedora"

inspector_id: 35

Hats

id: 558

style: "Ballcap"

inspector_id: 35

Hats

id: 559

style: "Silly"

inspector_id: 35


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• belongs_to :parent_class

• Sets Foreign Key

Belongs_To


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• has_many :child_class

• Builds Association in Ruby

Has_Many

i.e. Hat inspector has many hats


• How Does this Help?

• Related objects contain links to one another

• Get one object, you’ve got all associated

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>> myCustomer = Customer.where(:id => 2)

>> orders = myCustomer.orders.all

Has_Many


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• 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

• ...

Has_Many


• N+1 - (Cont.)

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customers = Customer.all

customers.each do |customer|

customer.orders do |order|

order.products do |product|

puts product

end

end

Associations

This would generate 10,001 database queries(not a good thing)


• N+1 - How do we Fix it?

• What if we could Pre-load Associations?

• Includes

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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Customer.includes(:orders => :products).all

Associations


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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

Has_Many :Through =>

What Classes have foreign keys?


• Physician Class

• Uses Appointments

• Finds Patients

• Automatically

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>> dr = Physicians.first

>> dr.patients

Has_Many :Through =>


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• HABTM (has and belongs to many)

• Creates direct many to many relationship

Has & Belongs To Many

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


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• Use HABTM

• Don’t need to do anything with the relationship model

• Restricted DB size

• Use :through

• Need validations

• Need callbacks

• Need extra attributes

HABTM - Vs. :Through


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Questions?http://guides.rubyonrails.orghttp://stackoverflow.com


http://stackoverflow.com

http://stackoverflow.com

Education

Rails 3 Beginner to Builder 2011 Week 3