A Practical Introduction to Domain Driven Design

Transcript

1. Please tell 2 others: 1. Why you are here today 2. What you want from today 3. To take a look at github.com/pelshoff/intro-ddd
2. A Practical Introduction To Domain Driven Design Twitter: @pelshoff @jlammerts
3. • has a cult following • works in all cases • only works if everyone commits • takes a lot more time • is only for experienced developers • goes well with event sourcing • doesn’t work without event sourcing • • is about documentation • is a new concept • is about strategy • is about tactics • is only for developers • is a hype • is for every project • is all-or-nothing • is about language • DDD... (true / false)
5. Approach • Reality • Model of the problem • Model of the solution • Working software
6. Today 1. Discovery 2. Design 3. Implementation 4. Integration
7. 1/4 Discovery
9. Noun Verb Verb Verb Verb Noun Noun Noun Noun
10. Context map • Repeat before interpret • Visualize structure • Learn (ubiquitous) language • First “feeling” for boundaries
11. Organizer Plans Event github.com/pelshoff/ Intro-ddd #User interviews • Organizer plans event • Organizer gets in touch with suppliers • etc.
12. Testing • Take one sentence • Run it through your map
14. Event Event Event Event Event Event Event Event Hot spot Decision
15. Discovery event storm • First interpretation • Visualize time • Learn (ubiquitous) language • Learn about issues (hot spots) • First “feeling” for boundaries
16. github.com/pelshoff/ Intro-ddd #User interviews • Event was planned • Suppliers were contacted • etc. Event Decision Hot spot Member was invoiced 14 days passed Invoice was paid Reminder was sent Including Sundays? Visitor arrived Has voting privileges Seated non-voting Seated voting How do we know?
17. Testing • Take a person • What happens to them • Run it through your process
18. 2/4 Design
19. Design • Design event storm • Choosing boundaries
21. Command Event Event Event Event Event Event ... Command Decision Command
22. github.com/pelshoff/ Intro-ddd #User interviews • Event was planned • Suppliers were contacted • etc. Event Decision Member was invoiced Command Send invoices Reminder was planned
23. Testing • Take a person • What they do • Run it through your process
24. 3/4 Implementation
26. Command
27. final class DoVote { private $decisionId; ... public function __construct(Uuid $decisionId, Uuid $memberId, Answer $answer) { $this->decisionId = $decisionId; $this->memberId = $memberId; $this->answer = $answer; } public function getDecisionId(): Uuid { return $this->decisionId; } ... }
28. Command • Data Transfer Object • Immutable • Capture intention
29. Command handler
30. final class DoVoteHander { public function handleDoVote(DoVote $doVote): void { // Voted // DecisionWasPassed // DecisionWasRejected } }
31. Command handler • Application Entry Point • When command, then event(s) • Implementation later
32. Work out some commands in code • Create command DTO’s • Create empty command handlers • Add comments for events No implementation! No framework! Get something started One service per command Use and adapt the event storm model Group project files by context
34. Value objects
35. final class Name { private $lastName; private $firstName; private $insertion; public function __construct(string $lastName, string $firstName, string $insertion) { $this->lastName = $lastName; $this->firstName = $firstName; $this->insertion = $insertion; $this->nameMustHaveLastName(); } private function nameMustHaveLastName(): void { if (!$this->lastName) { throw InvalidName::becauseLastNameIsMissing(); } } public function getLastName(): string { /**/ } public function getFirstName(): string { /**/ } public function getInsertion(): string { /**/ } }
36. final class EmailAddress { private $emailAddress; public function __construct(string $emailAddress) { $this->emailAddress = $emailAddress; $this->emailAddressMustBeAnActualEmailAddress(); } private function emailAddressMustBeAnActualEmailAddress(): void { if (!filter_var($this->emailAddress, FILTER_VALIDATE_EMAIL)) { throw InvalidEmailAddress::becauseThisIsNotAnEmailAddress(); } } public function asString(): string { return $this->emailAddress; } }
37. Value objects • Express a value • Define allowed values • Are immutable • Are easy to test
38. Entities
39. final class Member { private $id; private $name; private $emailAddress; public function __construct(Uuid $id, Name $name, EmailAddress $emailAddress) { $this->id = $id; $this->name = $name; $this->emailAddress = $emailAddress; } public function getId(): Uuid { /**/ } public function getName(): Name { /**/ } public function setName(Name $name): Attendee { /**/ } public function getEmailAddress(): EmailAddress { /**/ } public function setEmailAddress(EmailAddress $emailAddress): Attendee { $this->emailAddress = $emailAddress; return $this; } }
40. Entities • Have identity • Are more than their attributes • Evolve over time • Are slightly harder to test
41. Services
42. final class VotingOnDecision { private $repository; public function __construct(VoteRepository $repository) { $this->repository = $repository; } public function handleDoVote(DoVote $doVote): void { $this->memberMayOnlyVoteOnce($doVote); $this->repository->register($doVote); } private function memberMayOnlyVoteOnce(DoVote $doVote): void { try { $this->repository->find($doVote->getDecisionId(), $doVote->getMemberId()); } catch (VoteNotFound $e) { return; } throw VotingFailed::becauseMemberAlreadyVotedOnDecision(); } }
43. Services • Have no identity or attributes (Are not a “thing”) • Tackle cross-concern operations • Are harder to test
44. Repositories
45. interface VoteRepository{ public function register(DoVote $doVote): void; public function find(Uuid $decisionId, Uuid $memberId): Member; }
46. Repositories • Collection of all objects of a type • For now: interface only!
47. • Vendor ◦ PartyCongress ▪ Src • Domain ◦ Congress ▪ Congress.php ▪ Decision.php ▪ ListOfDecisions.php ▪ Vote.php ▪ VotingOnDecision.php ▪ VoteRepository.php ◦ Invoice ▪ PaidInvoices.php ◦ Membership ▪ Member.php ▪ MemberRepository.php ▪ Test • Congress ◦ CongressTest.php ◦ DecisionTest.php ◦ VotingOnDecisionTest.php
48. Work out the domain in code • Value Object: Immutable! • Entity: Life cycle! • Domain Service: Cross-concern process! • Repository: Complete set of a type of entity! No database! No browser! No generic subdomain! Focus on the domain Write unit tests Use and adapt the event storm model Group project files by context
49. 4/4 Integration
51. Domain Application Infrastructure Ui, Api’s, tests Layered architecture
52. Domain Application Database Api’s Ui Tests File system Messaging, etc. Hexagonal architecture (Ports & Adapters)
53. Ui, Api’s, integration- & acceptance tests Application Domain Infrastructure Big scary outside world Unit tests
54. • Vendor ◦ PartyCongress ▪ Src • App ◦ Congress ▪ DoVote.php ▪ DoVoteHandler.php ◦ Membership • Domain ◦ Congress ▪ Congress.php ▪ Decision.php ▪ ListOfDecisions.php ▪ VoteRepository.php ◦ Membership • Infrastructure ◦ Congress ▪ CachingVoteRepository.php ▪ InMemoryVoteRepository.php ▪ Test • Congress ◦ CongressTest.php ◦ DecisionTest.php ◦ VotingTest.php
55. • Vendor ◦ PartyCongress ▪ Src • App ◦ Congress ▪ DoVoteHandler.php • Domain ◦ Congress ▪ CongressRepository.php ▪ VoteRepository.php • Infrastructure ◦ Congress ▪ InMemoryCongressRepository.php • MyFrameworkOfChoice ◦ Bundles ▪ PartyCongressBundle • Infrastructure ◦ Congress ▪ DbalCongressRepository.php ▪ DbalVoteRepository.php • Ui ◦ Congress ▪ OnlineVotingController.php • Test ◦ Congress ▪ OnlineVotingFrontEndTest.php
56. Work out the integration in code • Connect the domain to your favorite framework, • Or to Plain-Old-C/PHP/Fortran/? • Make something work from UI to DB and back Database Browser End to end tests Group project files by concept
57. Please write two post-its with something you learned Pim Elshoff @pelshoff Joop Lammerts @jlammerts