Beyond MVC: from Model to Domain
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The document discusses software architectural patterns, particularly focusing on the Action Domain Responder (ADR) and Hexagonal Architecture (Ports and Adapters), elucidating their roles in managing complexity in web applications. It introduces Domain-Driven Design (DDD), emphasizing concepts like entities, value objects, aggregates, domain services, and domain events to model software effectively. Key insights include the importance of a shared language among team members and the encapsulation of domain logic for improved testability and maintainability.
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Beyond MVC: from Model to Domain
- 1. TrueNorthPHP 2014 Beyond MVC: From Model to Domain Jeremy Cook
- 2. What is a domain?
- 3. “a specified sphere of activity or knowledge.” –http://www.oxforddictionaries.com/definition/english/domain
- 4. “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…” –http://en.wikipedia.org/wiki/Domain_(software_engineering)
- 5. What is MVC?
- 6. Interaction of MVC Layers Model! User Manipulates Controller! Uses Updates View! Sees
- 7. Interaction of MVC Layers User Model! Controller! View!
- 8. 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
- 9. “Model–view–controller (MVC) is a software architectural pattern for implementing user interfaces.” –http://en.wikipedia.org/wiki/Model–view–controller
- 10. This talk is about managing complexity
- 11. Introducing Action Domain Responder
- 12. 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
- 13. What is Action Domain Responder? ❖ Model! ❖ View! ❖ Controller
- 14. What is Action Domain Responder? ❖ Controller! ❖ Model! ❖ View
- 15. What is Action Domain Responder? ❖ Controller Action! ❖ Model Domain! ❖ View Responder
- 16. 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
- 17. 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
- 18. 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
- 19. ADR Example <?php! ! interface ActionInterface {! public function __construct(ResponderFactoryInterface $factory);! public function __invoke(RequestInterface $request);! }!
- 20. 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();! }! }!
- 21. Further information on ADR ❖ https://github.com/pmjones/adr
- 23. Ports and Adapters Hexagonal Architecture
- 24. 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
- 25. What are Ports and Adapters? ❖ Invented by Alistair Cockburn! ❖ Architectural pattern for isolating an application from it’s inputs.
- 26. “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
- 27. “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
- 28. Ports and Adapters Application
- 29. Ports and Adapters Application
- 30. Ports and Adapters Adapters Adapters Application Adapters Adapters Adapters Adapters
- 31. Ports and Adapters Domain Adapters Adapters Adapters Adapters Adapters Adapters
- 32. 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);! }! }!
- 33. 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']);! }! }! }!
- 34. 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
- 35. Further information on Ports and Adapters ❖ The original article introducing ports and adapters: http://alistair.cockburn.us/Hexagonal+architecture
- 36. Introducing Domain Driven Design
- 37. What is Domain Driven Design? ❖ Concept coined by Eric Evans! ❖ Ideas can be grouped into two related areas:! ❖ Architectural patterns! ❖ Object patterns
- 39. Read some books
- 41. Your app has multiple domains
- 42. 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
- 43. 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
- 44. Context map ❖ Describes relationships between domains! ❖ Outlines all points of contact between domains! ❖ Can also include existing systems
- 45. Object patterns
- 46. Entities ❖ Represents a concept in your domain! ❖ Each instance of a entity should be considered unique! ❖ Houses logic and operation on the concept
- 47. 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
- 48. Value Objects <?php! ! class Person {! public function __construct($firstName, $lastName) {! //Code here! }! }! ! $person = new Person('Cook', 'Jeremy'); //WHOOPS!!
- 49. 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;! }! }!
- 50. 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'));!
- 51. Entities vs Value Objects !== Bank Account Owner: Jeremy Balance: $1,000,000 Account #: 12345 === Currency Name: Canadian Dollar Abbr: CAD Symbol: $ Bank Account Owner: Jeremy Balance: $1,000,000 Account #: 12346 Currency Name: Canadian Dollar Abbr: CAD Symbol: $
- 52. 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
- 53. 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
- 54. 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
- 55. 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);!
- 56. 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
- 57. Domain Events <?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);! $event = EventFactory::createEventForSuccessfulAccountTransfer($from, $to, $money);! $eventType = EventTypes::SUCCESSFUL_MONEY_TRANSFER;! $eventDispatcher->raiseEvent($eventType, $event);
- 58. 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
- 59. Avoid projects like this!
- 60. Thanks for listening! ❖ Any questions?! ❖ Feel free to contact me! ❖ [email protected]! ❖ @JCook21