jason sweat-design patterns

Sheraton Gateway Suite O'HareMay 20, 2008


Design Patterns in PHP


Jason E. Sweathttp://[email protected]

Design Patterns in PHP

Sheraton Gateway Suite O'HareMay 20, 2008 2Sheraton Gateway Suite O'HareMay 20, 2008

Technical Conference Presentation Pattern

2

• Design Pattern–The Classic Tech Talk

• Implementation:–Tell ‘em what your are going to tell ‘em–Tell ‘em–Tell ‘em what you told ‘em

• Forces:–Communication information to an audience

Sheraton Gateway Suite O'HareMay 20, 2008 3

The “Pattern” of this presentation

• Definition of Design Patterns

• Catalog of Design Patterns–Name and define each pattern–Review example PHP code–Forces driving use

• Conclusion


What is a Design Pattern?

• Commonly recognized, well developed and tested solution to a specific problem in a given context

• A specific way to organize a portion of your program—a code structure

• A name – a short hand way to communicate a design decision with other programmers familiar with patterns

• Obligatory reference: Christopher Alexander “A Pattern Language”


What a Design Pattern Isn’t

• Library• Framework• Copy & Paste Example Code


What a Design Pattern Isn’t

• Library• Framework• Copy & Paste Example Code

Your code and your problems are required to realize a design pattern.


Reification

• Reify - To make real• Reification – The process of making real

–Definition from “Holub on Patterns”


Pattern Usage

• Write code as usual• Feel a pain point (complex design issues,

bad code smells)• Be aware of Design Patterns, specifically

ones which solve the problem you are experiencing

• Refactor/write your code to apply the pattern to your problem

• Help apply DRY principal


Pattern Anti-Usage

• Big up front design–Plan which patterns you will need ahead of time–Violation of YAGNI

• Apply patterns where the problem they solve does not exist–Create complexity where there is no need for it–This applies to nearly every isolated example!!


Pattern Anti-Usage

• Big up front design–Plan which patterns you will need ahead of time–Violation of YAGNI

• Apply patterns where the problem they solve does not exist–Create complexity where there is no need for it–This applies to nearly every isolated example!!

Design Patterns can make coding complex problems easier.

Use them wisely and appropriately.


Design Pattern Online Resources

• PHP Related• http://www.patternsforphp.com/• http://www.phppatterns.com/ • http://www.sitepoint.com/forums/forumdisplay.php?f=147

• Classic • http://www.vincehuston.org/dp/ • http://c2.com/cgi/wiki?DesignPatterns • http://www.martinfowler.com/eaaCatalog/index.html • http://en.wikipedia.org/wiki/Design_pattern_

%28computer_science%29

http://www.patternsforphp.com/

http://www.patternsforphp.com/

http://www.phppatterns.com/

http://www.phppatterns.com/

http://www.sitepoint.com/forums/forumdisplay.php?f=147

http://www.sitepoint.com/forums/forumdisplay.php?f=147

http://www.vincehuston.org/dp/

http://www.vincehuston.org/dp/

http://c2.com/cgi/wiki?DesignPatterns

http://c2.com/cgi/wiki?DesignPatterns

http://www.martinfowler.com/eaaCatalog/index.html

http://www.martinfowler.com/eaaCatalog/index.html

http://en.wikipedia.org/wiki/Design_pattern_%2528computer_science%2529





Catalog Approach

• Name• Problem – what problem and context is the

pattern a solution to• Example – some concrete web application

related problems• Code – in PHP• Forces

–Why you would want to use this pattern–What would cause you to avoid it

Many pattern catalogs are much more detailed. We are going to limit the scope of the catalog to these essential elements.


Singleton

• Problem: How can you make sure you are using a single instance of a class, and provide easy access to this instance?

• Example: database connections, factories, registries


Singleton

• Code

• Tests


Singleton - Forces

• For–Ensure object is configured correctly before

access–Ensure there is only one instance of the object

possible

• Against–Global access–Hard coding dependencies


Factory

• Problem: How can you centralize logic related to creation of objects?

• Example: Create instances of a CatalogItems


Factory

• Problem: How can you centralize logic related to creation of objects?

• Example: Create instances of a CatalogItems

There are several related creational patterns: FactoryMethod, AbstractFactory, Builder. In PHP, any method which returns an object is often referred to as a Factory. The dynamic typing of PHP may make implementing these in strict accordance with the patterns excessive for most projects needs.


FactoryMethod

• Class Diagram


FactoryMethod

• code


FactoryMethod

• More “PHPish” code


FactoryMethod - Code in action


FactoryMethod - Forces

• For–Isolate construction complexity–Promote decoupling code

• Against–One additional layer of indirection between the

construction of an object and it’s use


TemplateMethod

• Problem: How can you structure a class hierarchy to allow new implementations via subclassing?

• Example: different shipping calculation models in a shopping cart


TemplateMethod

• code


TemplateMethod

• Code continued


TemplateMethod

• Tests


TemplateMethod - Forces

• For–Lets subclasses vary algorithm behavior–Reduces code duplication

• Against–Forces inheritance


Strategy

• Problem: How can you encapsulate an algorithm in an object, so that it can be selected at run-time?



Strategy

• Problem: How can you encapsulate an algorithm in an object, so that it can be selected at run-time?


Quote seen on the internet: “Eventually, everything starts to look like a Strategy.” This is because the Strategy pattern implementation emphasizes the OO principal of polymorphism, making it very powerful in practice.


Strategy

• code


Strategy

• More code


Strategy

• Tests


Strategy - Forces

• For–Heart of favor composition over inheritance–Elimination of replicated control logic–Select “guts” of an object at run-time

• Against–Code complexity


State

• Problem: How can you allow an object to alter its behavior when its internal state changes, such that the object will appear to change its class?–Put another way: How can I implement an object

which behaves like the Strategy pattern, but can change Strategies over the lifetime of the object

• Example: same shopping cart checkout–Perhaps you want to list the shipping rates for all

available options reusing the strategy code already implemented in the prior example


State - Code


State

• Tests


State – Forces

• For–Power of Strategy with more flexibility

• Against–Similar code complexity as Strategy


Proxy

• Problem: How can you provide surrogate control to an object?

• Example: remote resources, lazy instantiation, access control


Proxy (Access)

• Code


Proxy (Access)

• Tests


Proxy (Lazy)

• Code


Proxy – Forces

• For–Need to add additional functionality without

changing the original classes responsibilities–Need flexibility to change functionality after the

object is already instantiated

• Against–Is the flexibility required?


Decorator

• Problem: How can you add capabilities to an object dynamically?

• Example: caching, error/warning indication

The Decorator pattern can allow you to “trump” inheritance, allowing you to deploy a very flexible solution without repeating code in many locations inside of a class hierarchy.


Decorator

• Illustrating the problem in UML– A hypothetical widget library to generate forms

– But we might want to have some widgets labeled…


Decorator

But sometimes you want to flag the control as in error after form validation, and this might apply to either the normal or a labeled widget…


Decorator

Yuck… and we only showed two kinds of “Widget”


Decorator


Decorator

• Code


Decorator


Decorator - Forces

• For–Eliminate code replication in class hierarchy–Flexibility–Powerful use of Polymorphism

• Against–Additional code to create the object–May be hard to understand the effects of objects

decorated multiple times


SPL

• Standard PHP Library• Documentation

–Official - http://www.php.net/manual/en/ref.spl.php–Real - http://www.php.net/~helly/php/ext/spl/

• SPL is a collection of interfaces and classes that are meant to solve standard problems.–Many SPL classes implement design patterns

http://www.php.net/manual/en/ref.spl.php

http://www.php.net/manual/en/ref.spl.php

http://www.php.net/~helly/php/ext/spl/

http://www.php.net/~helly/php/ext/spl/


Iterator

• Problem: How can you process a collection of objects in a uniform manner?

• Examples: arrays, directories/files, db record sets, XML elements


Iterator

• foreach is your friend• Hooray for object handles!


Iterator

• If you are too lazy to look up the methods in the Iterator interface, PHP will let you know:


Iterator - Code


Iterator

• Tests


Iterator - Forces

• For–Uniform handling of different data sources

• Against–Can your code compete with an array?


Observer

• Problem: How can you effectively separate objects which produce data from objects which need to consume this data?

• Example: logging to one or more styles of output (text file, syslog, email, HTML output, etc.)


Observer


Observer

• In SPL – interfaces


Observer

• Code – • A Subject


Observer

• Code – putting it to use:


Observer

• Tests


Observer - Forces

• For–Effective separation of the producer of data from

the consumers

• Against–The common theme – code complexity, did you

really need the flexibility Observer provides?


A pair of Data Access Patterns

• In PHP, nearly every application accesses data in a database – what patterns have evolved in this area?–ActiveRecord–TableDataGateway

CREATE TABLE `bookmark` ( ìd` INT NOT NULL AUTO_INCREMENT , ùrl` VARCHAR( 255 ) NOT NULL , `name` VARCHAR( 255 ) NOT NULL , `description` MEDIUMTEXT, `tag` VARCHAR( 50 ) , `created` DATETIME NOT NULL , ùpdated` DATETIME NOT NULL ,PRIMARY KEY ( ìd` ))


A database access library

• http://adodb.sf.net/ require_once 'adodb/adodb.inc.php';

class DB { //static class, we do not need a constructor private function __construct() {} public static function conn() { static $conn; if (!$conn) { $conn = adoNewConnection('mysql'); $conn->connect('localhost', 'phpauser‘ , 'phpapass', 'phpa'); $conn->setFetchMode(ADODB_FETCH_ASSOC); } return $conn; }}

http://adodb.sf.net/

http://adodb.sf.net/


ActiveRecord

• How can we have and object which both knows business logic and how to persist itself in a database?


ActiveRecord - Code

• Some properties

• And a little business logic – id is read only

class Bookmark { const NEW_BOOKMARK = -1; protected $id = -1; protected $conn; public $url; public $name; public $description; public $tag; public $created; public $updated; public function getId() { return $this->id; }}


ActiveRecord – Code – constructor, find self?

class Bookmark { const SELECT_BY_ID = 'select * from bookmark where id = ?'; public function __construct($id=false, $conn=false) { $this->conn = ($conn) ? $conn : DB::conn(); if ($id) { $rs = $this->conn->execute( self::SELECT_BY_ID ,array((int)$id));

if ($rs) { $row = $rs->fetchRow(); foreach($row as $field => $value) { $this->$field = $value; } } else { throw new Exception('DB Error: '.$this->conn->errorMsg()); } } }}


ActiveRecord – code

• Great, now we can find ourself, how can we make changes?

public function save() { if ($this->id == self::NEW_BOOKMARK) { $this->insert(); } else { $this->update(); } $this->setTimeStamps(); }


ActiveRecord – update()

const UPDATE_SQL = " update bookmark set url = ?, name = ?, description = ?, tag = ?, updated = now() where id = ? "; protected function update() { $this->conn->execute( self::UPDATE_SQL ,array( $this->url, $this->name, $this->description, $this->tag, $this->id)); }


ActiveRecord - Forces

• For–Simplest data pattern for “row at a time” handling

of data

• Against–Mixing data access and business logic in a single

class – low cohesion


TableDataGateway

• How can we give ourselves access to many rows of data from a table easily?


TableDataGateway - code

class BookmarkGateway { protected $conn; public function __construct($conn) { $this->conn = $conn; }

public function findAll() { $rs = $this->conn->execute('select * from bookmark'); if ($rs) { return $rs->getArray(); } else { throw new Exception('DB Error: ' .$this->conn->errorMsg()); } }}


TableDataGateway – add()

const INSERT_SQL = " insert into bookmark (url, name, description, tag , created, updated) values (?, ?, ?, ?, now(), now()) "; public function add($url, $name, $description, $group) { $rs = $this->conn->execute( self::INSERT_SQL ,array($url, $name, $description, $group)); if (!$rs) { throw new Exception('DB Error: '.$this->conn->errorMsg()); } }


TableDataGateway – Forces

• For–Simplest data pattern for multiple row access of

data from a table–Centralize database access for table in a single

location in your code

• Against–Managing code in separate locations – sql

statement is now located in a find method instead of embedded in code


Reading Resources


Reading Resources

• GoF - Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides Design Patterns: Elements of reusable object-oriented software. Addison-Wesley, 1995


Reading Resources


• PoEAA - Martin Fowler Patterns of Enterprise Application Architecture Addison-Wesley, 2003


Reading Resources



• Allen Holub Holub on Patterns: Learning design patterns by looking at code Apress, 2004

• Robert Martin Agile Software Development Prentice Hall, 2003• Clifton Nock Data Access Patterns Addison-Wesley, 2004• George Schlossnagle Advanced PHP Programming Sams Pub., 2004• Alan Shalloway and James R. Trott Design Patterns Explained, Addison-

Wesley, 2005• Rebecca Wirfs-Brock and Alan McKean Roles, Responsibilities and

Collaborations Addison-Wesley, 2003• Matt Zandstra Php 5 Objects, Patterns, Practice Apress, 2004


Reading Resources



• Allen Holub Holub on Patterns: Learning design patterns by looking at code Apress, 2004

• Robert Martin Agile Software Development Prentice Hall, 2003• Clifton Nock Data Access Patterns Addison-Wesley, 2004• George Schlossnagle Advanced PHP Programming Sams Pub., 2004• Alan Shalloway and James R. Trott Design Patterns Explained, Addison-

Wesley, 2005• Rebecca Wirfs-Brock and Alan McKean Roles, Responsibilities and

Collaborations Addison-Wesley, 2003• Matt Zandstra Php 5 Objects, Patterns, Practice Apress, 2004

• Jason E. Sweat Php Architect's Guide to Php Design Patterns Marco Tabini & Associates, 2005

jason sweat-design patterns

Documents

example code

pattern usage

factorymethod code

factorymethod code

aware of design patterns

pattern languagemay

pattern catalogs

design decision