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Given at TrueNorthPHP 2014: "MVC presents a great way to divide responsibilities in your application but it offers no help in building the most critical part: the model or domain. This talk will introduce ways that can help you to encapsulate the richness of your domain. We'll look at Action Domain Response as a new way of thinking about the concepts presented in MVC before examining Hexagonal Architecture, allowing you to easily reuse your domain across multiple delivery mechanisms. We'll then finish with an introduction to Domain Driven Design, a technique that allows you to closely align your domain with the business problems it is solving while helping keep things well designed and easily maintainable. By the end of this talk you should have the knowledge needed to begin modelling your domains more powerfully while keeping them aligned to the real world problems they solve."
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TrueNorthPHP 2014
Beyond MVC: From Model to Domain
Jeremy Cook
What is a domain?
–http://www.oxforddictionaries.com/definition/english/domain
“a specified sphere of activity or knowledge.”
–http://en.wikipedia.org/wiki/Domain_(software_engineering)
“A domain is a field of study that defines a set of common requirements, terminology, and functionality for any software program
constructed to solve a problem…”
What is MVC?
Interaction of MVC Layers
User
Model!
Controller!
Uses
Manipulates
View!
Updates
Sees
Interaction of MVC Layers
User
Model!
Controller!
View!
Problems with ‘web’ MVC
❖ Easy to muddy responsibilities in the controller!
❖ Use of the term ‘Model’ is an issue…!
❖ Offers no guidance in modelling the most critical part of our apps: the model or domain
–http://en.wikipedia.org/wiki/Model–view–controller
“Model–view–controller (MVC) is a software architectural pattern for implementing user
interfaces.”
This talk is about managing complexity
Introducing Action Domain Responder
What is Action Domain Responder?
❖ Created by Paul M Jones!
❖ Web specific refinement of MVC!
❖ Designed to map more closely to what actually happens in the lifecycle of a web request
What is Action Domain Responder?
❖ Model!
❖ View!
❖ Controller
What is Action Domain Responder?
❖ Controller!
❖ Model!
❖ View
What is Action Domain Responder?
❖ Controller Action!
❖ Model Domain!
❖ View Responder
Action
❖ In ADR an action is mapped to a single class or closure!
❖ Creates a single place for all code dealing with an action!
❖ Does not directly create a view or HTTP response
Responder
❖ ADR recognises that a web response is more than a view!
❖ Action instantiates a responder object and injects domain data in it!
❖ Responder is responsible for generating all aspects of the response
Domain
❖ ADR offers no help on modelling a domain…!
❖ …but at least Paul calls it a domain!!
❖ Other patterns later will offer more help here
ADR Example
<?php!!interface ActionInterface {! public function __construct(ResponderFactoryInterface $factory);! public function __invoke(RequestInterface $request);!}!
ADR Example
<?php!!class FooAction implements ActionInterface {! protected $responderFactory;!! public function __construct(ResponderFactoryInterface $factory) {! $this->responderFactory = $factory;! }!! public function __invoke(RequestInterface $request) {! //Domain logic here! $responder = $this->responderFactory->generateForRequest($request);!! return $responder();! }!}!
Hexagonal Architecture
Ports and Adapters Hexagonal Architecture
What’s wrong with ‘Hexagonal Architecture’?
❖ Has nothing to do with hexagons!
❖ Has nothing to do with the number 6!
❖ Ports and adapters describes what this actually does
What are Ports and Adapters?
❖ Invented by Alistair Cockburn!
❖ Architectural pattern for isolating an application from it’s inputs.
–Alistair Cockburn
“Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from
its eventual run-time devices and databases.”
–Alistair Cockburn
“Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from
its eventual run-time devices and databases.”
Ports and Adapters
Application
Ports and Adapters
Application
Ports and Adapters
Application
Adapters AdaptersA
dapt
ers A
dapters
AdaptersAdapters
Ports and Adapters
Domain
Adapters AdaptersA
dapt
ers A
dapters
AdaptersAdapters
HTTP Adapter<?php!!class FooAction implements ActionInterface {! protected $responderFactory;! protected $service;!! public function __construct(ResponderFactoryInterface $factory, ApplicationServiceInterface $service) {! $this->responderFactory = $factory;! $this->service = $service;! }!! public function __invoke(RequestInterface $request) {! $result = $this->service->__invoke($request->getParamsArray());! $responder = $this->responderFactory->generateForRequest($request);!! return $responder($result);! }!}!
AMQP Adapter<?php!!class FooConsumer implements AMQPConsumer {! protected $service;!! public function __construct(ApplicationServiceInterface $service) {! $this->service = $service;! }!! public function __invoke(AMQPMessage $msg) {! $data = json_decode($msg->body, true);! $result = $this->service->__invoke($data);! if ($result->isStatusOk()) {! $msg->delivery_info['channel']! ->basic_ack($msg->delivery_info['delivery_tag']);! }! }!}!
Advantages of Ports and Adapters
❖ Encapsulation of the domain!
❖ Allows development of the domain and adapters to be independent!
❖ Allows better end to end testability of the domain!
❖ Makes it simple to add new entry points to an app
Further information on Ports and Adapters
❖ The original article introducing ports and adapters: http://alistair.cockburn.us/Hexagonal+architecture
Introducing Domain Driven Design
What is Domain Driven Design?
❖ Concept coined by Eric Evans!
❖ Ideas can be grouped into two related areas:!
❖ Architectural patterns!
❖ Object patterns
DDD Interaction Map
Read some books
Architectural patterns
Your app has multiple domains
Ubiquitous language
❖ Develop a shared language to describe each domain and model the software after it!
❖ The domain should be an expression of the ubiquitous language in code!
❖ Aim is to unite all members of a product team, from developers to product managers
Bounded contexts
❖ Represents the boundary around a domain!
❖ All code within a domain is completely encapsulated with specific entry points!
❖ Code and concepts are unique per domain
Context map
❖ Describes relationships between domains!
❖ Outlines all points of contact between domains!
❖ Can also include existing systems
Object patterns
Entities
❖ Represents a concept in your domain!
❖ Each instance of a entity should be considered unique!
❖ Houses logic and operation on the concept
Value Objects
❖ Used when you only care about the attributes and logic of the concept!
❖ Immutable!
❖ All methods must be side effect free!
❖ Mutator methods must return a new instance of the value object!
❖ Prefer value objects over simple types
Value Objects
<?php!!class Person {! public function __construct($firstName, $lastName) {! //Code here! }!}!!$person = new Person('Cook', 'Jeremy'); //WHOOPS!!
Value Objects<?php!!class Firstname {! protected $firstname;!! public function __construct($firstname) {! if (! is_string($firstname)) {! throw new InvalidArgumentException(/**ErrorMessage**/);! }! $this->firstname = $firstname;! }!! public function __toString() {! return $this->firstname;! }!}!
Value Objects
<?php!!class Person {! public function __construct(Firstname $firstName, Lastname $lastName) {! //Code here! }!}!!//This will now cause an error!$person = new Person(new Lastname('Cook'), new Firstname('Jeremy'));!
Entities vs Value Objects
!==Bank AccountOwner: Jeremy
Balance: $1,000,000Account #: 12345
===Currency
Name: Canadian DollarAbbr: CADSymbol: $
CurrencyName: Canadian Dollar
Abbr: CADSymbol: $
Bank AccountOwner: Jeremy
Balance: $1,000,000Account #: 12346
Aggregates
❖ A collection of entities contained by another entity!
❖ The containing entity is the aggregate root!
❖ Individual aggregate instances can only be accessed through the aggregate root
Repositories
❖ A specialised adapter that maps entities to and from the persistence layer!
❖ Provides methods to retrieve entities and save them!
❖ Abstracts the details of the persistence layer away from the domain
Domain Services
❖ Encapsulates an operation that is not owned by another part of the domain model!
❖ A good service has three properties:!
❖ Models a domain concept that does not conceptually belong to an entity or value object!
❖ Stateless!
❖ Defined in terms of the domain model
Domain Services
<?php!!class MoneyTransfer {! public static function transferBetweenAccounts(Account $from, Account $to, Money $amount) {! $from->debitForTransfer($money, $to);! $to->creditFromTransfer($money, $from);! }!}!!//In the application service...!$from = $accountRepository->findByAccNumber('123456');!$to = $accountRepository->findByAccNumber('123457');!$money = new Money('100', new Currency('CAD'));!MoneyTransfer::transferBetweenAccounts($from, $to, $money);!
Domain Events
❖ Allows a domain to signal that something as happened!
❖ Full part of the domain and a representation of something that has happened!
❖ Used to signal something that might trigger a state change in another domain
Domain Events
$event = EventFactory::createEventForSuccessfulAccountTransfer($from, $to, $money);!$eventType = EventTypes::SUCCESSFUL_MONEY_TRANSFER;!$eventDispatcher->raiseEvent($eventType, $event);
<?php!!class MoneyTransfer {! public static function transferBetweenAccounts(Account $from, Account $to, Money $amount) {! $from->debitForTransfer($money, $to);! $to->creditFromTransfer($money, $from);! }!}!!//In the application service...!$from = $accountRepository->findByAccNumber('123456');!$to = $accountRepository->findByAccNumber('123457');!$money = new Money('100', new Currency('CAD'));!MoneyTransfer::transferBetweenAccounts($from, $to, $money);!
Further Information on DDD❖ Eric Evans!
❖ “Domain Driven Design” book!
❖ Short introduction: https://domainlanguage.com/ddd/patterns/DDD_Reference_2011-01-31.pdf!
❖ Implementing Domain Driven Design by Vaughn Vernon!
❖ Mathias Verraes: http://verraes.net!
❖ DDD in PHP Google Group: https://groups.google.com/forum/#!forum/dddinphp
Avoid projects like this!
Thanks for listening!
❖ Any questions?!
❖ Feel free to contact me!
❖ @JCook21
