Introduction to Domain-Driven Design in PHP - ZendCon & OpenEnterprise 2018

Building PHP applications using domain-driven design (DDD) techniques results in code that is easier to modify, maintain, test, and makes for a better user experience. In this hands-on tutorial, you will become versed in the best practices for solving problems in PHP from start to finish.
You will learn to:
– Discover a ubiquitous language and identify changes in the design of PHP classes, methods, and problem solving
– Assemble an incorruptible domain model in PHP by encapsulating business logic in immutable value objects, specifications, and entities
– Employ best practices for persisting and accessing entities and aggregate roots in Doctrine and Zend DB and Hydrator
– Use advanced PHP object-oriented techniques to simplify code and reduce state complexity
– Plan for change by using the Hexagonal Architecture Pattern
– Evaluate when and how to use CQRS techniques
– Write your own DIY event sourcing and use libraries like EventSauce and Prooph
– Introduce DDD to a “legacy” codebase
– Discover recommended resources for learning more about applying DDD in PHP

Transcript

1. Domain-Driven Design Workshop Domain-Driven Design Workshop Andrew Cassell @alc277 andrewcassell.com
6. Domain-Driven Design
7. Domain-Driven Design
9. Common Sense Software Development
16. Encapsulation & Immutability & Modeling & Behavior
17. Domain
18. Domain
19. BEER
21. Photo: Kathleen Pierce - Bangor Daily News
28. Brewing Software
33. recipe hop grain hop_inventory grain_inventory recipe_hop_link user recipe_user_link brew_event ROLE_USER ROLE_ADMIN
34. Source: http://jonclaytonbiz.com/
37. People don't want to buy a quarter-inch drill, they want a quarter-inch hole. Theodore Levitt
41. #JBTD (http://jobstobedone.org/)
43. YYYYY
44. Why? Why? Why? Why? Why?
45. Search Caluclation List Automation
46. DDD !=
52. http://www.csharpstar.com/
54. DDD CRUD Correctness Testability Usability Maintainability Modifiability
56. DDD BALL OF MUD / CRUD Correctness Testability Usability Maintainability Modifiability
57. DDD CRUD/MUD Recipe Building Inventory Brewhouse Activity Beer Menu / Prices Brew Sessions Brewery Website Calclations QA Record Keeping
58. Who is responsible
63. Ubiquitous Language
64. Ubiquitous Language Developers Domain Experts
65. Ubiquitous Language
66. User Brewer Employee Taster Customer
68. 1. Naming Things 2. Cache Invalidation 3. Off By One Errors Top 10 Reasons Programming is Hard
69. $recipe = BeerRecipe::findOrFail($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();
71. Ubiquitous Language $recipe->addGrains($grains); Code: We need to be able to add a measured amount of grain to a recipe. Business:
72. Ubiquitous Language $recipe->getEstimatedAlcoholByVolumeABV(); Code: We need to be able to calculate an estimated ABV for a recipe. Business:
73. 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.
74. 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:
75. @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“
76. $recipe->dryHop($hop); $recipe->addIngredient($hop); $recipe->addToBoil($hop); $recipe->addToBoilKettle($hop); $recipe->addToBoiler($hop); $recipe->addFirstWortHop($hop); $recipe->addToFermenter($hop); $recipe->addToMashTun($hop); //fails
77. $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());
78. $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());
79. CRUD/MUD DDD Users Brewers String RecipeName Integer IBU Float(7,3) AlphaAcid Array of ORM Objects GrainBill BeerInventoryRepositoryInterface Menu
80. […], 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.
81. DDD BALL OF MUD/CRUD Correctness ✓ Testability Usability Maintainability Modifiability
83. The Brewer, designed and engraved in the Sixteenth Century, by Jost Amman.
84. Inventory Marketing Finance Production “Hop”
85. Quantity at a Location Flavor Expenditure Ingredient “Hop”
86. Bounded Contexts
87. Inventory Recipes Brewhouse
88. Slide: Vaughn Vernon
90. Inventory Recipes Brewhouse
91. Inventory Recipes Brewhouse
92. Message Inventory Recipes Brewhouse
93. Domain Event Inventory Recipes Brewhouse
99. Personas
100. adaptivepath.com
101. 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.
106. https://blog.intercom.io/using-job-stories-design-features-ui-ux/
109. 7 Dirty Words When Meeting With a Domain Expert 1.Session 2.Repository 3.Abstract 4.Interface 5.Class 6.Database 7.Foreign Key
110. User Research
111. Photo: Mathias Verraes
112. Command Actor Model Domain Event
113. Domain Event • Something that happens in the software. • Past Tense
114. Domain Event • Beer Was Brewed • Grain Was Added • Hops Were Added • Brewer Changed Email Address
124. Command Actor Model Domain Event
125. Command • The action that precipitates the event • Written in Present Tense
126. Command • Start Brewing Session • Add Grain to Recipe • Add Hops To Fermenter • Change Email Address
129. Command Actor Model Domain Event
130. Model • Command is acted upon this thing • Might Include Supporting Models
131. Model • Recipe • Ingredient • Brewer
133. Command Actor Model Domain Event
134. Actor • Who did it? • If you only have one user you might not need this
137. Command Actor Model Domain Event
141. Source: Jeff Patton
143. business origami
144. Jess McMullin Business Origami
145. Jess McMullin Business Origami
146. Sean Jalleh
148. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability Usability ✓ Maintainability Modifiability
149. Domain Objects Value Objects Domain Events Entities Aggregates
150. 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
151. Value Objects
152. Email Address Recipe Name Date We Brewed On Weight Temperature Value Objects
153. Value Objects Email Address Recipe Name Date We Brewed On Weight Temperature Ubiquitous Language
154. Value Objects EmailAddress RecipeName BrewedOn Pounds DegreesFahrenheit Email Address Recipe Name Date We Brewed On Weight Temperature
155. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md Value Objects
156. Immutable
157. Immutable Avoid Spooky Action at a Distance
158. ALWAYS VALID Value Objects
159. Value Objects
160. “Gateway Drug to Test Driven Development” Value Objects
161. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
162. Plain Old PHP Objects (POPOs) Value Objects
163. 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
164. Only depend on scalars or other value objects. Value Objects
165. They are not dependencies that you inject. Value Objects
166. RecipeName Example
171. 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.
175. 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)
178. BrewedOn Example
182. Pounds Example
186. $poundA->reduceBy($poundB);
187. Eliminates Checking Value Objects
189. Static Constructors
190. Natural Language Constructors
193. Temperature Example
199. Composite Value Objects
200. Full Name First Name + Last Name
202. Encoding Business Logic in Value Objects
205. Amount of Alcohol
207. ABV
208. Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2
209. Sugar + Yeast = Alcohol + CO2
210. Sugar - Sugar = Alcohol START FINISH
211. Sugar - Sugar = Alcohol START FINISH Volume Volume
212. Specific Gravity
213. Hydrometer
214. learntomoonshine.com
234. DDD CRUD/MUD RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?
235. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability Modifiability
237. Entities
238. 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
239. DO AS MUCH AS YOU CAN IN VALUE OBJECTS!
240. Doctrine Mappings Doctrine Annotations Laravel Eloquent ORM “Storage Agnostic”
241. BEHAVIOR FIRST! STORAGE SECOND! “Storage Agnostic”
242. Single Entity Entities Regular Aggregate Contain Other Entities
243. Brewer Grain Hops BeerOnTap Entity Types Regular Aggregate Invoice Recipe BrewSession BeerMenu
244. 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, …
246. SETTERS ARE BAD
251. Calling two setters in a row on the same object Missing a Concept?
252. Calling two methods in a row on the same object Missing a Concept?
253. Passing more than one parameter to a method Missing a Concept?
256. Doctrine
270. Bounded Contexts
271. Inventory Recipes Brewhouse
272. Inventory Recipes Brewhouse Recipe\Grain Inventory\Grain Brewing\BrewSession\Grain
273. Inventory Recipes Brewhouse
274. Inventory Recipes Brewhouse Brewers Supporting Bounded Context
275. Mathias Verraes - Mathias Verraes - Emergent Boundaries https://www.youtube.com/watch?v=ECM1rPYxvD4
276. • Entities • Manages Child Entities • Transactional Boundary • The Easiest Models to Identify Aggregates
277. Aggregates Recipe BrewSession BeerMenu
284. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓ Maintainability ✓✓ Modifiability ✓
285. Task Based User Interface
289. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓ Modifiability ✓
291. Security
292. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
293. Controller Domain Framework
298. Controller Domain Framework
299. Mathias Verraes - Decoupling the Model from the Framework at Laracon EU 2014 https://www.youtube.com/watch?v=QaIGN_cTcc8
300. Ruby Midwest 2011 - Keynote: Architecture the Lost Years by Robert Martin https://www.youtube.com/watch?v=WpkDN78P884
302. Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates
303. DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modifiability ✓
304. Domain Events
305. 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
307. BrewSessionWasPlanned
308. BrewSessionWasPlanned
316. DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modifiability ✓✓
318. Command Query Responsibility Segregation
319. CQRS
320. Write Read
321. Write Model Read Model(s)
322. Write Domain Model Read Model(s)
323. Write Domain Model Read (Complicated SQL Queries)
324. Controller Command Bus Handler Handler Handler
325. Controller Command Bus Handler Handler Handler Request
326. Controller Command Bus Handler Handler Handler Command
329. Controller Command Bus Handler Handler Handler Command
330. Controller Command Bus Handler Handler Handler Command
331. Controller Command Bus Handler Handler Handler Command
332. Controller Command Bus Handler Handler Handler Command Response
333. Controller Command Bus Handler Handler Handler Command
334. Controller Command Bus Handler Handler Handler Response
335. Controller Command Bus Handler Handler Handler Response
336. Controller Command Bus Handler Handler Handler Response
337. https://gnugat.github.io/ 2016/05/11/towards-cqrs- command-bus.html
339. Why Do CQRS?
340. Controller Domain Framework
341. Controller API (versions?) Console Commands
342. Command Bus Command Query Responsibility Segregation
343. Write Domain Model Read Model(s)
344. Event Sourcing
348. Event Sourcing • Object Properties are Not Persisted • Events Are Persisted to 
 Append Only Event Storage
349. • Avoids Data Mapping • Avoids Object-relational Impedance Mismatch • Reduces Database Table Counts (Related Tables) • Potentially Reduces Model Counts Event Sourcing
350. Slide: Microsoft
351. Libraries • https://github.com/eventsaucephp • https://github.com/broadway • https://github.com/prooph • https://github.com/szjani/predaddy
352. Recipe Example
353. Learning More
354. homebrewersassociation.org
357. DEV BOOK CLUB https://www.youtube.com/user/devbookclub
364. DDDinPHP Google Group http://DDDinPHP.org
365. Final Thoughts
370. Inventory Recipes Brewhouse
371. Inventory Recipes Brewhouse Legacy Context
373. Value Objects “Light”
374. Andrew Cassell @alc277 andrewcassell.com Immutability to Save an Ever-Changing World
377. https://joind.in/talk/93cfd DDD Topics Covered •Ubiquitous Language •Event Storming •Modelling •Value Objects •Entities •Aggregates •Hexagonal Architecture •CQRS •Event Sourcing