Domain-driven Design in PHP - PHP Benelux 2018

Building PHP applications using Domain-driven design techniques results in code that is easier to modify, maintain, and test, and a better user experience. Once you try DDD, you will never design software in the same way again.

In this tutorial, we will start by learning how to build a strong ubiquitous language with stakeholders. Then, we will learn the benefits of encapsulating business logic in value objects using test-driven development.

Next, we will move on to using bounded contexts, entities, and aggregate roots to manage state and protect invariants. We will also cover more advanced topics in the DDD world, such as event sourcing and command query responsibility segregation.

No prior knowledge of domain-driven design required.

https://conference.phpbenelux.eu/2018/sessions/domain-driven-design-in-php/

Transcript

1. Domain-Driven Design Workshop Domain-Driven Design Workshop Andrew Cassell @alc277 andrewcassell.com
10. Domain-Driven Design
11. Domain-Driven Design
13. Common Sense Software Development
24. Encapsulation & Immutability & Modeling & Behavior
25. Domain
26. Domain
27. BEER
32. Photo: Kathleen Pierce - Bangor Daily News
44. Brewing Software
55. recipe hop grain hop_inventory grain_inventory recipe_hop_link user recipe_user_link brew_event ROLE_USER ROLE_ADMIN
56. Source: http://jonclaytonbiz.com/
59. People don't want to buy a quarter-inch drill, they want a quarter-inch hole. Theodore Levitt
63. #JBTD (http://jobstobedone.org/)
65. YYYYY
66. Why? Why? Why? Why? Why?
67. Search Caluclation List Automation
68. DDD !=
74. http://www.csharpstar.com/
76. DDD CRUD Correctness Testability Usability Maintainability Modifiability
78. DDD BALL OF MUD / CRUD Correctness Testability Usability Maintainability Modifiability
79. DDD CRUD/MUD Recipe Building Inventory Brewhouse Activity Beer Menu / Prices Brew Sessions Brewery Website Calclations QA Record Keeping
80. Who is responsible
85. Ubiquitous Language
86. Lingua franca
87. Ubiquitous Language
88. Ubiquitous Language Developers Domain Experts
89. Ubiquitous Language
90. User Brewer Employee Taster Customer
92. 1. Naming Things 2. Cache Invalidation 3. Off By One Errors Top 10 Reasons Programming is Hard
93. $recipe = BeerRecipe::findOrFail($uuid);
 $hop = HopRepo::where(“name”,”=“,”Simcoe”)->take(1)->get(); 
 if (!$recipe->hopsArray()->contains(‘hop_id’,$hop->id)) {
 
 $recipe->hopsArray()->attach($hop->id, [‘weight' => 1.0]);
 }
 
 
 $recipe->save();
95. Ubiquitous Language $recipe->addGrains($grains); Code: We need to be able to add a measured amount of grain to a recipe. Business:
96. Ubiquitous Language $recipe->getEstimatedAlcoholByVolumeABV(); Code: We need to be able to calculate an estimated ABV for a recipe. Business:
97. Ubiquitous Language $storage = (new StorageFacilities())->findByOneName(“Silo #4”); $storage->howMuchOfGrainType(new GrainType(‘Winter Wheat’)); Business: Code: We need to know how much Winter Wheat is in our storage silo #4.
98. Ubiquitous Language $recipe->addDryHop($hopQuantity,$schedule); Code: We need to add .2oz of 12% AA per gallon of Simcoe hops to a recipe 7 days after the boil is complete. This is called dry hopping. $schedule = new DryHopSchedule(‘7 Days’); $hopQuantity = HopQuantity::(“Simcoe”,”12%AA”,”.2oz per gallon”); Business:
99. @recipe Feature: A user should be able to dry hop a recipe Scenario: User adds dry hops to recipe Given I am authenticated as a user And I am on “/recipe/0ef360fd“ And I press "Add Hops” And I fill out form with: | Hop Name | | Simcoe | Then I see “Alpha Acid: 11.5 - 15.0“
100. $recipe->dryHop($hop); $recipe->addIngredient($hop); $recipe->addToBoil($hop); $recipe->addToBoilKettle($hop); $recipe->addToBoiler($hop); $recipe->addFirstWortHop($hop); $recipe->addToFermenter($hop); $recipe->addToMashTun($hop); //fails
101. $hop = (new HopsSupply(…))->findOneByName(‘Simcoe’); $catalog = new RecipeCatalog(…); $recipe = $catalog->findOneRecipeByName(‘iPHPA’); $recipe->addDryHop($hop, new DryHopSchedule(‘7 Days’)); $brewers = new Brewers(…); $brewer = $brewers->findOneByUsername(‘cassell’); $brewSession = $brewer->brew($recipe); $brewSession->dryHopsWereAdded($hop, Datetime::now());
102. $hop = (new HopsSupplyRepo())->findOneByName(‘Simcoe’); $catalog = new RecipeCatalogRepository(…); $recipe = $catalog->findOneRecipeByName(‘iPHPA’); $recipe->addDryHop($hop, new DryHopSchedule(‘7 Days’)); $brewers = new BrewersRepository(…); $brewer = $brewers->findOneByUsername(‘cassell’); $brewSession = $brewer->brew($recipe); $brewSession->dryHopsWereAdded($hop, Datetime::now());
103. CRUD/MUD DDD Users Brewers String RecipeName Integer IBU Float(7,3) AlphaAcid Array of ORM Objects GrainBill BeerInventoryRepositoryInterface Menu
107. $hop = (new HopsSupply())->findOneByName(‘Centennial Pellets’); $catalog = new RecipeCatalog(…); $recipe = $catalog->findOneRecipeByName(‘iPHPA’); $recipe->addDryHop($hop, new DryHopSchedule(‘7 Days’)); $brewers = new Brewers(…); $brewer = $brewers->findOneByUsername(‘cassell’); $brewSession = $brewer->brew($recipe); $brewSession->dryHopsWereAdded($hop, Datetime::now());
108. […], 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.
109. DDD BALL OF MUD/CRUD Correctness ✓ Testability Usability Maintainability Modifiability
111. The Brewer, designed and engraved in the Sixteenth Century, by Jost Amman.
112. Inventory Marketing Finance Production “Hop”
113. Quantity at a Location Flavor Expenditure Ingredient “Hop”
114. Bounded Contexts
115. Inventory Recipes Brewhouse
116. Slide: Vaughn Vernon
118. Inventory Recipes Brewhouse
119. Inventory Recipes Brewhouse
120. Message Inventory Recipes Brewhouse
121. Domain Event Inventory Recipes Brewhouse
127. Personas
128. adaptivepath.com
129. Photos: Terry Brown and Gordon Stettinius Alice Shane P.J. Sam George Male Age 32 Brewer for 3 Years Got into brewing after the record store he worked at closed. Is very tech savvy and carries an Android. Male Age 50 Brewing for 10 Years Just Promoted to COO Retired civil servant who believes software can make a brewery for regulatory compliant. Female Age 27 New Hire Library science graduate who was just hired away from the local university. iPhone user. Male Age 52 Librarian for 30 years Has been brewing beer as long as he can remember. Loves beer podcasts but is not a fan of technology. Male Age 46 Brewer for 20 Years Loves poetry and writing. Brewing is just a job to pay the bills.
134. https://blog.intercom.io/using-job-stories-design-features-ui-ux/
137. 7 Dirty Words When Meeting With a Domain Expert 1.Session 2.Repository 3.Abstract 4.Interface 5.Class 6.Database 7.Foreign Key
138. User Research
139. Photo: Mathias Verraes
140. Command Actor Model Domain Event
141. Domain Event • Something that happens in the software. • Past Tense
142. Domain Event • Beer Was Brewed • Grain Was Added • Hops Were Added • Brewer Changed Email Address
152. Command Actor Model Domain Event
153. Command • The action that precipitates the event • Written in Present Tense
154. Command • Start Brewing Session • Add Grain to Recipe • Add Hops To Fermenter • Change Email Address
157. Command Actor Model Domain Event
158. Model • Command is acted upon this thing • Might Include Supporting Models
159. Model • Recipe • Ingredient • Brewer
161. Command Actor Model Domain Event
162. Actor • Who did it? • If you only have one user you might not need this
165. Command Actor Model Domain Event
168. business origami
169. Jess McMullin Business Origami
170. Jess McMullin Business Origami
171. Jess McMullin Business Origami
172. Sean Jalleh
175. Source: Jeff Patton
181. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability Usability ✓ Maintainability Modifiability
182. Domain Objects Value Objects Domain Events Entities Aggregates
183. Value Object Immutable No Identity (Only Values) Hop Name Amount Paid Temperature Entity Identifiable Mutable Lifecycle Contains Value Objects Line Item Brewer Water Chemistry Aggregate Entity Responsible For Child Entities Transaction Boundary Invoice Recipe Brew Session
184. Value Objects
185. Email Address Recipe Name Date We Brewed On Weight Temperature Value Objects
186. Value Objects Email Address Recipe Name Date We Brewed On Weight Temperature Ubiquitous Language
187. Value Objects EmailAddress RecipeName BrewedOn Pounds DegreesFahrenheit Email Address Recipe Name Date We Brewed On Weight Temperature
188. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md Value Objects
189. Immutable
190. Immutable Avoid Spooky Action at a Distance
191. ALWAYS VALID Value Objects
192. Value Objects
193. “Gateway Drug to Test Driven Development” Value Objects
194. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
195. Plain Old PHP Objects (POPOs) Value Objects
196. Plain Old PHP Objects (POPOs) • Declare Class Properties as Private • No Setters (behaviors will return new) • No References to Mutable Objects • Throw Exceptions in Constructor Value Objects
197. Only depend on scalars or other value objects. Value Objects
198. They are not dependencies that you inject. Value Objects
199. RecipeName Example
204. cassell:beeriously cassell$ docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app --user : --workdir /app beeriously_php-fpm /app/vendor/bin/phpunit --configuration /app/src/Tests/Unit/ phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. FEE 3 / 3 (100%) Time: 2.34 seconds, Memory: 4.00MB There were 2 errors: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testGetter Error: Class 'Beeriously\Domain\Recipe\RecipeName' not found /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:20 2) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Error: Class 'Beeriously\Domain\Recipe\RecipeName' not found /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:26 -- There was 1 failure: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testEmptyFails Failed asserting that exception of type "Error" matches expected exception "Beeriously\Domain\Recipe\InvalidRecipeNameException". Message was: "Class 'Beeriously\Domain\Recipe\RecipeName' not found" at /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:15 . ERRORS! Tests: 3, Assertions: 1, Errors: 2, Failures: 1.
206. cassell:beeriously cassell$ docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app --user : --workdir /app beeriously_php-fpm /app/ vendor/bin/phpunit --configuration /app/src/Tests/Unit/phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. .EE 3 / 3 (100%) Time: 1.56 seconds, Memory: 4.00MB There were 2 errors: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testGetter Error: Call to undefined method Beeriously\Domain\Recipe\RecipeName::getValue() /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:21 2) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Object of class Beeriously\Domain\Recipe\RecipeName could not be converted to string /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:27 ERRORS! Tests: 3, Assertions: 2, Errors: 2. cassell:beeriously cassell$
208. docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app -- user : --workdir /app beeriously_php-fpm /app/vendor/bin/phpunit --configuration /app/ src/Tests/Unit/phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. ..E 2 / 3 (67%) Time: 292 ms, Memory: 4.00MB There was 1 error: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Object of class Beeriously\Domain\Recipe\RecipeName could not be converted to string /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:27 ERRORS! Tests: 35, Assertions: 78, Errors: 1. make: *** [unit] Error 2 cassell:beeriously cassell$
210. cassell:beeriously cassell$ docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app --user : --workdir /app beeriously_php-fpm /app/vendor/bin/phpunit --configuration /app/src/Tests/ Unit/phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. ... 3 / 3 (100%) Time: 192 ms, Memory: 4.00MB OK (3 tests, 4 assertions)
213. BrewedOn Example
217. Pounds Example
221. $poundA->reduceBy($poundB);
222. Eliminates Checking Value Objects
224. Static Constructors
225. Natural Language Constructors
228. Temperature Example
234. Composite Value Objects
235. Full Name First Name + Last Name
237. Encoding Business Logic in Value Objects
240. Amount of Alcohol
242. ABV
243. Sugar + Yeast = Alcohol + CO2
244. Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2
245. Sugar + Yeast = Alcohol + CO2
246. Sugar + Yeast = Alcohol + CO2
247. Sugar - Sugar = Alcohol START FINISH
248. Sugar - Sugar = Alcohol START FINISH Volume Volume
249. Specific Gravity
251. Hydrometer
253. learntomoonshine.com
254. Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2
274. DDD CRUD/MUD RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?
275. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability Modifiability
277. Entities
278. Identifiable Have State and are Mutable (Lifecycle) Never in an Invalid State Operate using Value Objects No Security or Permission Checks *(Ideally) Storage Agnostic Entities
279. DO AS MUCH AS YOU CAN IN VALUE OBJECTS!
280. Doctrine Mappings Doctrine Annotations Laravel Eloquent ORM “Storage Agnostic”
281. BEHAVIOR FIRST! STORAGE SECOND! “Storage Agnostic”
282. Single Entity Entities Regular Aggregate Contain Other Entities
283. Brewer Grain Hops BeerOnTap Entity Types Regular Aggregate Invoice Recipe BrewSession BeerMenu
284. Making an Entity: Brewer Identifiable ID (UUID) Mutable $brewer->changeUsername $brewer->changeName $brewer->changeEmail Never in an Invalid State __construct Operate Using Value Objects FullName, EmailAddress, …
286. SETTERS ARE BAD
291. Calling two setters in a row on the same object Missing a Concept?
292. Calling two methods in a row on the same object Missing a Concept?
293. Passing more than one parameter to a method Missing a Concept?
296. Doctrine
306. Bounded Contexts
307. Inventory Recipes Brewhouse
308. Inventory Recipes Brewhouse Recipe\Grain Inventory\Grain Brewing\BrewSession\Grain
309. Inventory Recipes Brewhouse
310. Inventory Recipes Brewhouse Brewers Supporting Bounded Context
311. Mathias Verraes - Mathias Verraes - Emergent Boundaries https://www.youtube.com/watch?v=ECM1rPYxvD4
312. • Entities • Manages Child Entities • Transactional Boundary • The Easiest Models to Identify Aggregates
313. Aggregates Recipe BrewSession BeerMenu
322. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓ Maintainability ✓✓ Modifiability ✓
323. Business Rules in a Specification
327. DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓ Maintainability ✓✓ Modifiability ✓
328. Task Based User Interface
332. DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓ Modifiability ✓
334. Security
335. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
336. Controller Domain Framework
341. Controller Domain Framework
342. Mathias Verraes - Decoupling the Model from the Framework at Laracon EU 2014 https://www.youtube.com/watch?v=QaIGN_cTcc8
343. Ruby Midwest 2011 - Keynote: Architecture the Lost Years by Robert Martin https://www.youtube.com/watch?v=WpkDN78P884
346. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
347. DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modifiability ✓
348. Domain Events
349. 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
351. BrewSessionWasPlanned
352. BrewSessionWasPlanned
360. DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modifiability ✓✓
362. Command Query Responsibility Segregation
363. CQRS
364. Write Read
365. Write Model Read Model(s)
366. Write Domain Model Read Model(s)
367. Write Domain Model Read (Complicated SQL Queries)
368. Controller Command Bus Handler Handler Handler
369. Controller Command Bus Handler Handler Handler Request
370. Controller Command Bus Handler Handler Handler Command
373. Controller Command Bus Handler Handler Handler Command
374. Controller Command Bus Handler Handler Handler Command
375. Controller Command Bus Handler Handler Handler Command
376. Controller Command Bus Handler Handler Handler Command Response
377. Controller Command Bus Handler Handler Handler Command
378. Controller Command Bus Handler Handler Handler Response
379. Controller Command Bus Handler Handler Handler Response
380. Controller Command Bus Handler Handler Handler Response Command
381. Controller Command Bus Handler Handler Handler Response
382. https://gnugat.github.io/ 2016/05/11/towards-cqrs- command-bus.html
385. Controller Command Bus Handler Handler Handler Response Command
386. Controller Command Bus Handler Handler Handler Response
391. Why Do CQRS?
392. Controller Domain Framework
393. Controller API (versions?) Console Commands
394. Command Bus Command Query Responsibility Segregation
395. Write Domain Model Read Model(s)
396. Event Sourcing
400. Event Sourcing • Object Properties are Not Persisted • Events Are Persisted to 
 Append Only Event Storage
401. • Avoids Data Mapping • Avoids Object-relational Impedance Mismatch • Reduces Database Table Counts (Related Tables) • Potentially Reduces Model Counts Event Sourcing
402. Slide: Microsoft
403. Libraries • https://github.com/broadway • https://github.com/prooph • https://github.com/szjani/predaddy
404. Recipe Example
405. Learning More
406. homebrewersassociation.org
409. DEV BOOK CLUB https://www.youtube.com/user/devbookclub
415. DDDinPHP Google Group http://DDDinPHP.org
416. Final Thoughts
421. Inventory Recipes Brewhouse
422. Inventory Recipes Brewhouse Legacy Context
426. Value Objects “Light”
427. Andrew Cassell @alc277 andrewcassell.com Immutability to Save an Ever-Changing World
428. https://joind.in/talk/93cfd DDD Topics Covered •Ubiquitous Language •Event Storming •Modelling •Value Objects •Entities •Aggregates •Hexagonal Architecture •CQRS •Event Sourcing