SOLID - It's Not Just a State of Matter, It's Principles for OO Propriety

SOLID
Not Just a State of Matter, It’s Principles for OO Propriety
Chris Weldon
Saturday, June 30, 12

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Me
• Fightin’ Texas Aggie
• PHP Developer since 2003
• Senior Consultant at Improving Enterprises
• mojolive.com/proﬁle/neraath
• Contact Me: [email protected]

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apihackday.com

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TOMORROW
• Free!
• Food, Drinks, and Beer Provided
• $750 Amazon Cert, $250 Apple Cert, Other Prizes
• Register NOW: http://apihackday.com

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What is OOD?

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What is OOD?
Abstraction

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What is OOD?
Inheritance
Abstraction

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What is OOD?
Encapsulation
Inheritance
Abstraction

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What is OOD?
Encapsulation Polymorphism
Inheritance
Abstraction

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?

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An Order

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class Order
{
private $_id;
private $_userId;
private $_products;
public function getId() {
return $this->_id;
}
public function setId($id) {
$this->_id = $id;
}
public function getUserId() {
return $this->_userId;
}
public function setUserId($userId) {
$this->_userId = $userId;
}

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public function getProducts() {
return $this->_products;
}
public function addProduct($product) {
$this->_products->add($product);
}
public function setProducts(Product[] $products) {
$this->_products = $products;
}

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New Requirement!
Calculate Cost of Order

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class OrderUtilities
{
public static function calculateCostOfOrder($order)
{
$products = $order->getProducts();
$cost = 0.0;
foreach ($products as $product) {
$cost += $product->getCost();
}
return $cost;
}

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New Requirements!
Fetch Orders from Database
Fetch User for Order

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public static function getOrderById($orderId)
{
if ($orderId == null || $orderId < 0)
{
$command = $this->_db->exec("SELECT * FROM orders");
$results = $this->_db->getResults($command);
// Get the first result.
return $results[0];
}
$command = $this->_db->exec("SELECT * FROM orders WHERE id = ?", $orderId);
$order = $this->_db->getSingle($command);
return $order;
}

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public static function getUserForOrder($order)
{
$command = $this->_db->exec("SELECT * FROM users WHERE id = ?", $order->getUserId());
$user = $this->_db->getSingle($command);
return $user;
}

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New Requirements!
Deliver Order to Customer
Notify Customer of Delivery

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public static function deliverOrder()
{
try {
$networkConnection = new WebServiceConnection("http://shpt1/shipctrl.svc");
$networkConnection->open();
$shippingManager = new ShippingManager($networkConnection);
$shippingManager->setOrder($this);
$shippingManager->setDeliveryType(DeliveryType::EXPRESS);
$shippingManager->shipViaWebService();
$this->notifyCustomer();
} catch (\Exception $e) {
$logFile = fopen("/tmp/logfile.log", "a");
fwrite("An error occurred while delivering the order.", $logFile);
fclose($logFile);
}
}

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public static function notifyCustomer()
{
try {
$mailer = new \Zend_Mail();
$mailer->setFrom('[email protected]', 'Grumpy Baby Orders');
$mailer->setSubject('Order #' . $this->getId() . ' out for Delivery');
$mailer->setBodyText('Your order is being shipped!');
$mailer->send();
} catch (\Exception $e) {
self::logNotificationError($errorMessage);
}
}

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public static function logDeliveryError($errorMessage)
{
fwrite("An error occurred while delivering the order.", $logFile);
fwrite($errorMessage, $logFile);
fclose($logFile);
}
public static function logNotificationError($errorMessage)
{
fwrite("An error occurred while emailing the notice.", $logFile);
fwrite($errorMessage, $logFile);
fclose($logFile);
}
}

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OMG

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OMG
Who vomited in my codebase?

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“There should never be more than one reason
for a class to change”

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Improve

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Improve
class Order
{
// I’m just a model
}

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Improve
class Order
{
}
class OrderDao
{
// I just talk to the database
public function CreateOrder($userId,
array $products);
public function getOrderById($orderId);
}

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Improve
class Order
{
}
class OrderDao
{
array $products);
}
class OrderDeliverer
{
// I just deliver orders
public function deliverOrder();
}

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Improve
class Order
{
}
class OrderDao
{
array $products);
}
{
}
class CustomerNotifier
{
public function notifyCustomer();
}

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Improve
class Order
{
}
class OrderDao
{
array $products);
}
{
}
class CustomerNotifier
{
public function notifyCustomer();
}
it’s what we do

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Zend_Log
kLogger
log4php
log5php
pear/Log

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Next Sample

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public function ActivateDrillBit($customerOption) {
if ($customerOption == "small") {
$drillBit = new SmallBit();
$drillBit->activate();
} else if ($customerOption == "medium") {
$drillBit = new MediumBit();
$drillBit->activate("120hz");
} else if ($customerOption == "large") {
$drillBit = new LargeBit();
$drillBit->activate("240hz", Options::Water);
}
}

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Customer Needs to Specify Options
Requirements Change!

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public function ActivateDrillBit($customerOption, $freq, Options $options)
{
if ($freq == "") $freq = "240hz";
if ($options == null) $options = Options::NoWater;
if ($customerOption == "small") {
$drillBit = new SmallBit();
$drillBit.activate($freq, $options);
} else if (customerOption == "medium") {
$drillBit = new MediumBit();
} else if (customerOption == "large") {
$drillBit = new LargeBit();
}
}

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You
Broke
My
App
!@#!@

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class DrillBitActivator {
// ...
}
}
class DrillBitConfigurableActivator implements DrillBitActivator {
public __construct($freqency, Options $options) {
// Configurable!
}
// ...
}
}

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public function ActivateDrillBit($customerOption)
/** @var IDrillBit $drillBit */
$drillBit = DrillBitFactory::CreateDrillBit($customerOption);
$drillBit.activate($this->_freq, $this->_options);
}

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Next

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A Familiar Example

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interface IManageCustomers {
function TakeSpecifications(Specs $specs);
function ReviewSpecifications(Specs $specs);
function GiveToEngineers(Specs $specs);
function DealWithTheGoshDarnCustomers();
function IsPeoplePerson();
}

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class GoodManager implements IManageCustomers {
public function TakeSpecifications(Specs $specs) {
$this->ReviewSpecifications($specs);
}
public function ReviewSpecifications(Specs $specs) {
// If specs seem good.
$this->GiveToEngineers($specs);
}
public function GiveToEngineers(Specs $specs) {
// E-mails specs to engineers.
}
public function DealWithTheGoshDarnCustomers() {
// You better believe he does.
}
public function IsPeoplePerson() {
return true; // Absolutely!
}
}

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class Tom implements IManageCustomers {
throw new DelegateToSecretary();
}
}
}
// Your gosh darn right I do!
}
return true; // I AM a people person, dammit!
}
}

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Our consultants have a look at Tom

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interface ITakeSpecifications {
function TakeSpecifications(Specs $specs);
}
interface IReviewSpecifications {
function ReviewSpecifications(Specs $specs);
}
interface IGiveToEngineers {
function GiveToEngineers(Specs $specs);
}
interface IManageCustomers {
function DealWithTheGoshDarnCustomers();
function IsPeoplePerson();
}

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class GoodManager implements
IManageCustomers, ITakeSpecifications, IReviewSpecifications, IGiveToEngineers
{
$this->ReviewSpecifications($specs);
}
// If specs seem good.
$this->GiveToEngineers($specs);
}
// E-mails specs to engineers.
}
// You better believe he does.
}
return true; // Absolutely!
}
}

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class Tom implements IManageCustomers {
// Your gosh darn right I do!
}
return true; // I AM a people person, dammit!
}
}

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Next Up

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interface IDataResource
{
function Load();
function Save();
}

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class AppSettings implements IDataResource {
public function Load() {
// Load application settings.
}
public function Save() {
// Save application settings.
}
}

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class UserSettings implements IDataResource {
// Load user settings.
}
// Save user settings.
}
}

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static function LoadAll() {
$resources = array(
new AppSettings(),
new UserSettings()
);
foreach ($resources as $resource) {
$resource->Load();
}
return $resources;
}
static function SaveAll(array $resources) {
$resource->Save();
}
}

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Our “Duck”

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class UnsaveableSettings implements AppSettings {
// Loads settings.
}
throw new CannotSaveException();
}
}

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$resources = array(
new AppSettings(),
new UserSettings(),
new UnsaveableSettings()
);
$resource->Load();
}
return $resources;
}
static function SaveAll(array resources) {
$resource->Save();
}
}

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$resources = array(
new AppSettings(),
new UserSettings(),
);
$resource->Load();
}
return $resources;
}
static function SaveAll(array resources) {
$resource->Save();
}
}
What happens with UnsaveableSettings?

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if ($resource instanceof UnsaveableSettings) continue;
$resource->Save();
}
}
teh ﬁx!

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if ($resource instanceof UnsaveableSettings) continue;
$resource->Save();
}
}
teh ﬁx!
omg shoot me
good job reducing abstraction

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The Real Fix

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The Real Fix
Interface Segregation +
Polymorphism

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interface IDataResource
{
function Load();
}
interface ISaveResource
{
function Save();
}

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public class AppSettingsLoaderBase implements IDataResource {
public void Load() {
// Load application settings.
}
}

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public class AppSettings extends AppSettingsLoaderBase
implements ISaveResource {
// Save application settings.
}
}

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public class UnsaveableSettings extends AppSettingsLoaderBase {
public void Load() {
// Loads settings.
}
}

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$resources = array(
new AppSettings(),
new UserSettings(),
);
foreach ($resources as $resources) {
$resource->Load();
}
return $resources;
}
static function SaveAll(SaveResourcesCollection $resources) {
$resource->Save();
}
}

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Final Problem

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class Authenticator {
/** @var DataAccessLayer $_repository */
private $_repository;
public __construct() {
$this->_repository = new DataAccessLayer();
}
public function authenticate($username, $password) {
$hashedPassword = md5($password);
$user = $this->_repository->findByUsernameAndPassword(
$username, $hashedPassword);
return $user == null;
}
}

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Problems?

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Problems?
authenticate() : bool
Authenticator
ﬁndByUsernameAndPassword : array
DataAccessLayer

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Problems?
Authenticator
DataAccessLayer
Strongly coupled to DataAccessLayer

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Dependency Inversion
• “High-level modules should not depend upon low level modules. They
should depend upon abstractions.
• “Abstractions should not depend upon details. Details should depend
upon abstractions.”
Robert Martin

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Step 1
Invert Dependency

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public __construct(DataAccessLayer $repository) {
$this->_repository = $repository;
}
}
}

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Coupling = Bad

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Step 2
Depend on Abstractions

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interface IUserRepository {
function findByUsernameAndPassword($username, $password);
}
class DataAccessLayer implements IUserRepository {
public function findByUsernameAndPassword($username, $password) {
// Do some database stuff.
}
}

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/** @var IUserRepository $_repository
public __construct(IUserRepository $repository) {
$this->_repository = $repository;
}
}
}

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Comparison

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Comparison
Authenticator
DataAccessLayer

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Comparison
Authenticator
DataAccessLayer
Authenticator
IUserRepository
DataAccessLayer

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Beneﬁt: Flexibility
class WebServiceUserRepository implements IUserRepository {
// Fetch our user through JSON or SOAP
}
}
public class OAuthRepository implements IUserRepository {
// Connect to your favorite OAuth provider
}
}

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Recap

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S = SRP - Single Responsibility Principle

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O = OCP - Open/Closed Principle

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L = LSP - Liskov Substitution Principle

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I = ISP - Interface Segregation Principle

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I = ISP - Interface Segregation Principle
D = DIP - Dependency Inversion Principle

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?

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Is it law?

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They be more like
“guidelines”

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Questions?

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http://joind.in/talk/view/6345
Thanks!

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Dependency Injection

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What is it?

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Involves a Service Container
Involves a Service
Container

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sfServiceContainer Subclass
class UserRepositoryContainer extends sfServiceContainer {
protected function getUserRepositoryService() {
$container = new DataAccessLayer($this['repository.config']);
return $container;
}
}

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Just Ask The Container for a
Service

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Consuming the Container
class LoginController {
public function login($username, $password) {
$container = new UserRepositoryContainer();
$repository = $container->userRepository;
$authenticator = new Authenticator($repository);
if ($authenticator->authenticate($username, $password)) {
// Do something to log the user in.
}
}
}

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Registers Chains of
Dependencies

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Code-Based Description
// Imagine this is a bootstrap file.
$configuration = Zend_Registry::get('dbconfig');
$builder = new sfServiceContainerBuilder();
$builder->register('user_repository', 'DataAccessLayer')
->addArgument($configuration)
// OR ->addArgument('%repository.config%') from earlier
->setShared(false);
$builder->register('authenticator', 'Authenticator')
->addArgument(new sfServiceReference('user_repository'));
Zend_Registry::set('di_container', $builder);

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Conﬁg-Based Description

mysql://localhost/database
username
password

%user_repository.dsn%
%user_repository.username%
%user_repository.password%


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Get the Object You Want

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Using the Container
class LoginController {
public function login($username, $password) {
$container = Zend_Registry::get('di_container');
$authenticator = $container->authenticator;
if ($authenticator->authenticate($username, $password)) {
// Do something to log the user in.
}
}
}

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Deep Topic

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SOLID - It's Not Just a State of Matter, It's Principles for OO Propriety

SOLID - It's Not Just a State of Matter, It's Principles for OO Propriety

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