Software Design Patterns

1

Design Patterns

Daniel WaligóraWrocław 09/01/2012

2

Bibliography• Martin Fowler,Patterns of Enterprise Appication

Architecture

• Matt Zandstra , PHP5 Objects, Patters, and Practice

• http://www.ustream.tv - New York PHP channel

• Symfony Live Berlin 2012 - https://joind.in/event/view/1114

• http://scholar.google.pl

• http://pzielinski.com

3

Gang of Four

4

Breakdown Design Patterns by GoF

Design Design PatternsPatterns

creationcreationalal

structurstructuralal

behaviorbehavioralal

- abstract factory- builder- prototype

- decorator

- facade- composite

- observer

- strategy- command

5

6

7

Implementation related to the

contextprogrammiprogrammi

ng ng languagelanguage

scalabilityscalability

modularitymodularitytestable testable

(integration (integration test)test)

time-time-consumingconsuming

size of size of projectproject

8

Context Context ISIS related to the related to the programming programming

languagelanguage

Design Design patterns patterns IS IS NOTNOT related related

to the to the programminprogramming languageg language

9

Transaction Script1. class Hotel  2. {   3. private 4. $_gateway;

5.     public function __construct(Data_Access_Gateway $gateway)    6.     {    7.         $this->_gateway = $gateway;    8.     }    9.   10.     public function bookRoom($userId, $fromDate, $toDate)    11.     {    12.         $roomId = $this->_gateway->_getRoomIdBetweenDates($fromDate, $toDate);    13.   14.         if (!$roomId) {    15.             return false;    16.         }    17.   18.         $days = $this->_getAmountOfDays($fromDate, $toDate);    19.   20.         if ($days < = 7) {  21.             $price = $days * 100;  22.         } else {   23.             $price = $days * 80;  24.         }  25.           26.         $data = array(  27.             'userId' => $userId,    28.             'roomId' => $roomId,  29.             'fromDate' => $fromDate,    30.             'toDate' => $toDate,    31.             'price' => $price,    32.         );    33.   34.         $bookingId = $this->_gateway->insert('bookings', $data);    35.   36.         return $bookingId;    37.     }    38. } 

10

Transaction Script

• simple procedural model

•works well with a simple data access layer

• easy implementation of use cases

• difficult to maintenance

• code duplication

Disadvantages:Advantages:

11

Table Module #11. class Hotel  2. {    3.     public function __construct(Data_Access_Gateway $gateway, Booking $booking)    •     {    •         $this->_gateway = $gateway;  •         $this->_booking = $booking;  •     }    •   •     public function bookRoom($userId, $fromDate, $toDate)    •     {    •         $roomId = $this->_booking->getRoomBetweenDates($fromDate, $toDate);  •   •         if (!$roomId) {    •             return false;    •         }    •   •         $days = $this->_getAmountOfDays($fromDate, $toDate);    •   •         if ($days < = 7) {  •             $price = $days * 100;  •         } else {   •             $price = $days * 80;  •         }  •           •         $bookingId = $this->_booking-

>addBooking($userId, $roomId, $fromDate, $toDate, $price);    •   •         return $bookingId;    •     }    • }  •   

12

Table Module #21. class Booking  2. {    3.     public function __construct(Data_Access_Gateway $gateway)    4.     {    5.         $this->_gateway = $gateway;    6.     }  7.       8.     public function getRoomBetweenDates($dateFrom, $dateTo)  9.     {  10.        return $this->_gateway->getRoomBetweenDates($dateFrom, $dateTo);  11.    }  12.      13.    public function addBooking($userId, $roomId, $fromDate, $toDate, $price)    14.    {    15.        $data = array(  16.            'userId' => $userId,    17.            'roomId' => $roomId,  18.            'fromDate' => $fromDate,    19.            'toDate' => $toDate,    20.            'price' => $price,    21.        );    22.  23.        $bookingId = $this->_gateway->insert('bookings', $data);    24.  25.        return $bookingId;    26.    }    27.}  

13

Table Module vs Transaction Script

• less duplication

• encapsulation

•more organized and structured code

• easy implementation by technology support

•weak support for polymorphism

• no support ORM

Disadvantages:Advantages:

14

Domain Model #11. class Hotel  2. {    3.     protected $_hotelId;  4.     protected $_rooms;  5.       6.     public function bookRoom(User $user, $fromDate, $toDate)    7.     {    8.         $room = $this->_getRoomBetweenDates($fromDate, $toDate);  9.   10.         if (is_null($room)) {    11.             return false;    12.         }    13.   14.         $booking = $room->bookRoom(User $user, $fromDate, $toDate);  15.   16.         return $booking;    17.     }  18. }  19.   20. class Room  21. {  22.     protected $_roomId;  23.     protected $_bookings = array();  24.       25.     public function bookRoom(User $user, $fromDate, $toDate)  26.     {  27.         $days = $this->_getAmountOfDays($fromDate, $toDate);  28.           29.         if ($days < = 7) {  30.             $booking = new Booking($user, new ShortBookingStrategy($user, $days));  31.         } else {   32.             $booking = new Booking($user, new NormalBookingStrategy($user, $days));  33.         }  34.           35.         return $booking;  36.     }  37. } 

15

Domain Model #21. class NormalBookingPriceStrategy extends BookingPriceStrategy  2. {  3.     public function getPrice()  4.     {  5.         $price = $this->_days * 80;  6.           7.         if ($this->_user->isLoyal()) {  8.             $price = $price / 2;  9.         }  10.          11.        return $price;  12.    }  13.}  14.  15.class ShortBookingPriceStrategy extends BookingPriceStrategy  16.{    17.    public function getPrice()  18.    {  19.        return $this->_days * 100;  20.    }  21.}

16

Domain Model vs Procedural Pattern

• prevents logic duplication

•more code readability

• independence from the data source

•much easier to unit test

• time-consuming implementation

• additional patterns

- ORM

- data source

Disadvantages:Advantages:

17

SUMMARYprogrammiprogrammi

ng ng languagelanguage

scalabilityscalability

modularitymodularity

testable testable (integration (integration

test)test)

time-time-consumingconsuming

size of size of projectproject

skill of the developers

18

Don’t be STUPID,GRASP SOLID!

19

Sorry, but your code is STUPID!

20

1.class DB 2.{  3.    private static $instance;

4.  public static function getInstance()5.    {  6.        if(!isset(self::$instance)) {  7.            self::$instance = new self;  8.        }  9.          10.        return self::$instance;  11.    }  12.}  

•Singleton

21

Dupleton ?

21

•Singleton (ctd)1. class DB 2.{  3.    private static $instance;

•   public static function getInstance()•     {  •         if(!isset(self::$instance)) {  •             self::$instance = new self;  •         }  •           •         return self::$instance;  •     }  • }  

• class Order • {  •     protected $db;

•   public function __construct()•     {  •         $this->db = DB::getInstance();           •     }  • }

22

•Singleton (ctd)

1. class DB 2.{3. //body4.}

5. class Order 6.{  •     protected $db;

•   public function __construct(DB $db)•     {  •         $this->db = $db;           •     }  • }

23

•Tight Coupling

1.Order::buy();

1. class House 2.{3. public function __construct()• {• $this->door = new Door();• $this->window = new Window();• }• }

1. class House 2.{3. public function __construct(Door $door, Window

$window)• {• $this->door = $door;• $this->window = $window;• }• }

24

•Untestable Code

I donI don’’t t have a have a time!time!

25

Never Make CodeFaster Than Necessary,Something Important Is

Always Lost When You Do

•Premature Optimization

26

•Premature Optimization (ctd)

Performance Performance problemsproblems 20%20% of code of code

27

•Indescriptive Naming

char * strpbrk ( const char *, const char * );

??

28

•Indescriptive Naming (ctd)

Code is Read Far More Often Than Written

29

DRY (Don’t Repeat Yourself!)

KISS (Keep It Smile, Stupid!)

•Duplication

30

•Singleton

•Tight Coupling

•Untestable Code

•Premature Optimization

•Indescriptive Naming

•Duplication

31

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

32

33

Test Driven-Development

34

Advantages of Design Pattern?

•speed up the development process,

•helps to prevent issues that can cause major problems,

•patterns allow developers to communicate using well-known, well understood names for software interactions

35

EoTThank You