Domain-Driven Design

Talk given at PHP Serbia 2017:
(http://www.conf2017.phpsrbija.rs/)

Transcript

1. Domain-Driven Design Deconstructed Domain-Driven Design Deconstructed Andrew Cassell @alc277 andrewcassell.com
6. Domain-Driven Design
7. Domain-Driven Design
14. Domain
15. Domain
16. Penn State Pattee Library
17. book user book_inventory book_inventory_user_link ROLE_USER ROLE_ADMIN
18. Source: http://jonclaytonbiz.com/
21. People don't want to buy a quarter-inch drill, they want a quarter-inch hole. Theodore Levitt
24. Common Sense Software Development
25. DDD !=
32. DDD CRUD Correctness Testability Usability Maintainability Modifiability
33. DDD BALL OF MUD / CRUD Correctness Testability Usability Maintainability Modifiability
38. Ubiquitous Language
39. Ubiquitous Language Developers Domain Experts
40. Ubiquitous Language
41. User Customer Client Member Employee
43. 1. Naming Things 2. Cache Invalidation 3. Off By One Errors Top 10 Reasons Programming is Hard
44. CRUD/MUD DDD Users Members BookInventoryRepository LibraryCatalog String ISBN Float(7,3) DeweyDecimal
45. $user = User::findOrFail($uuid);
 $book = Books::where('isbn', '=', $isbn)->take(1)->get();
 
 
 if (!$user->userBookLinks()->contains($book->id) && $user->borrowLinks->count() < 5) {
 
 $user->userBookLinks()->attach($book->id, ['date_due' => new DateTime('+2 Weeks')];
 
 }
 
 
 $user->save();
47. $catalog = new LibraryCatalog(…); $book = $catalog->findOneBookByISBN($isbn); $members = new Members(…); $borrower = $members->findOneByAccountNumber($acctNumber); $borrower->borrow($book);
48. $borrower->borrow($book); $borrower->loan($book); $borrower->obtain($book); $borrower->rent($book);
49. @library @loan Feature: A member should be able to borrow a book Scenario: Member borrows a book Given I am authenticated as a librarian And I am on “/member/behat-123" And I press "Borrow Book" And I fill out form with: | ISBN | | 978-032-112521-7 | Then I see "Domain-driven Design"
50. @library @loan Feature: A member should be able to borrow a book Scenario: Member borrows a book Given I am authenticated as a librarian And I am on “/member/behat-123" And I press "Borrow Book" And I fill out form with: | ISBN | | 978-032-112521-7 | Then I see "Domain-driven Design"
51. […], we want to establish the idea that a computer language is not just a way of getting a computer to perform operations but rather that it is a novel formal medium for expressing ideas about methodology. Thus, programs must be written for people to read, and only incidentally for machines to execute.
52. DDD BALL OF MUD/CRUD Correctness ✓ Testability Usability Maintainability Modifiability
57. Sales Marketing Finance Production
58. Customer Lead Payee ShipTo
59. Slide: Vaughn Vernon
61. Billing Loan Catalog
62. Billing Loan Catalog
63. Billing Loan Catalog Message
64. Billing Loan Catalog Domain Event
70. 7 Dirty Words When Meeting With a Domain Expert 1.Session 2.Repository 3.Abstract 4.Interface 5.Class 6.Database 7.Foreign Key
71. User Research
72. Photo: Mathias Verraes
79. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability Usability Maintainability Modifiability
80. Domain Objects Value Objects Entities Aggregates Domain Events
81. Value Object Immutable No Identity (Only Values) Book Title Amount Paid ISBN Number Entity Identifiable Mutable Lifecycle Contains Value Objects Book Librarian Invoice Aggregate Entity Responsible For Child Entities Transaction Boundary Member Library
82. Book Title Dewey Decimal Number Date Borrowed ISBN Number Email Address Value Objects
83. BookTitle DeweyDecimalNumber DateBorrowed ISBNNumber EmailAddress Value Objects
84. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md Value Objects
85. Immutable Avoid Spooky Action at a Distance
86. ALWAYS IN A VALID STATE Value Objects
87. Value Objects
88. “Gateway Drug to Test Driven Development” Value Objects
89. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
90. Plain PHP Objects (POPOs) Value Objects
91. Plain PHP Objects (POPOs) • Declare Class Properties as Private • No Setters • No References to Mutable Objects • Throw Exceptions in Constructor Value Objects
92. BookTitle Example
100. DateBorrowed Example
102. RenewalsRemaining Example
105. Example LoanPeriod
108. DDD CRUD/MUD BookTitle String BookCondition String ISBN String DeweyDecimal Float(7,3) DateBorrowed DateTime
109. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability Maintainability Modifiability
111. Librarian Library Book Entities
112. Identifiable Have State and are Mutable Never Invalid State Operate Using Value Objects No Security or Permission Checks Storage Agnostic Entities
117. Doctrine
121. SETTERS ARE BAD
127. • Special Kind of Entity • Manages Child Entities • Transaction Boundary Aggregates
128. Aggregates Member FinesInvoice
134. Task Based User Interface
137. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability Modifiability
139. Security
140. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
141. Controller Domain Framework
146. Controller Domain Framework
147. Mathias Verraes - Decoupling the Model from the Framework at Laracon EU 2014 https://www.youtube.com/watch?v=QaIGN_cTcc8
148. Ruby Midwest 2011 - Keynote: Architecture the Lost Years by Robert Martin https://www.youtube.com/watch?v=WpkDN78P884
149. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
150. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability ✓ Modifiability
151. Domain Events
152. Domain Events • Part of the Core Domain • Happened In The Past • Important Enough To Record (Persist) • Important Enough To Concern Other Bounded Contexts • Immutable Value Objects • Do Not Contain Entities or Other Mutable Objects • Can Be Created in an Entity
157. DamagedBookWasRemovedFromCirculation
158. DamagedBookWasRemovedFromCirculation
164. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability ✓ Modifiability ✓
165. Command Query Responsibility Segregation
166. CQRS
167. Write Read
168. Write Model Read Model(s)
169. Write Domain Model Read Model(s)
170. Controller Command Bus Handler Handler Handler
171. Controller Command Bus Handler Handler Handler Request
172. Controller Command Bus Handler Handler Handler Command
174. Controller Command Bus Handler Handler Handler Command
175. Controller Command Bus Handler Handler Handler Command
176. Controller Command Bus Handler Handler Handler Command
177. Controller Command Bus Handler Handler Handler Response
178. Controller Command Bus Handler Handler Handler Response
179. Controller Command Bus Handler Handler Handler Response
180. Controller Domain Framework
181. https://gnugat.github.io/ 2016/05/11/towards-cqrs- command-bus.html
183. Event Sourcing
187. • Avoids Data Mapping • Avoids Object-relational Impedance Mismatch • Reduces Database Table Counts (Related Tables) • Potentially Reduces Model Counts Event Sourcing
188. Event Sourcing • Object Properties are Not Persisted • Events Are Persisted to Append Only Event Storage
192. Libraries • https://github.com/broadway • https://github.com/prooph • https://github.com/szjani/predaddy
193. Learning More
195. DEV BOOK CLUB https://www.youtube.com/user/devbookclub
200. DDDinPHP Google Group http://DDDinPHP.org
203. https://joind.in/talk/e8752 DDD Topics Covered •Ubiquitous Language •Event Storming •Modelling •Value Objects •Entities •Aggregates •Hexagonal Architecture •CQRS •Event Sourcing