Domain-driven Design Workshop

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D ain-D iven Design Workshop D ain-D iven Design Workshop Andrew Cassell @alc277 andrewcassell.com

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available on

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1 About CURIOSITYSTREAM • Founded by John Hendricks, founder of the Discovery Channel • Thousands of documentaries and series • HD and 4K • Available worldwide

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4 WE ARE HIRING! https://jobs.daxx.com/browse-jobs/?search_keywords=curiositystream

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github.com/cassell

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BEER

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Good Code?

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Testable SOLID Less Defensive

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Monolith Microservices Serverless

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Domain-Driven Design

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Domain-Driven Design

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Common Sense Software Development

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$car->bark(); $dog->drive();

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Encapsulation Modeling Behavior

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Domain

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available on

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BEER

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Photo: Kathleen Pierce - Bangor Daily News

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Brewing Software

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recipe hop grain hop_inventory grain_inventory recipe_hop_link user recipe_user_link brew_event ROLE_USER ROLE_ADMIN

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Source: http://jonclaytonbiz.com/

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People don't want to buy a quarter-inch drill, they want a quarter- inch hole. Theodore Levitt

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#JBTD (http://jobstobedone.org/)

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YYYYY why? why? why? why? why?

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Why? Why? Why? Why? Why?

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Search Caluclation List Automation

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DDD !=

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http://www.csharpstar.com/

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DDD CRUD Correctness Testability Usability Maintainability Modiﬁability

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DDD BALL OF MUD / CRUD Correctness Testability Usability Maintainability Modiﬁability

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DDD CRUD/MUD Recipe Building Inventory Brewhouse Activity Beer Menu / Prices Brew Sessions Brewery Website Calclations QA Record Keeping

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Who is responsible

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Ubiquitous Language

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Ubiquitous Language Developers Domain Experts

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Ubiquitous Language

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User Brewer Employee Taster Customer

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1. Naming Things 2. Cache Invalidation 3. Off By One Errors Top 10 Reasons Programming is Hard

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$recipe = BeerRecipe::findOrFail($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();

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Ubiquitous Language $recipe->addGrains($grains); Code: We need to be able to add a measured amount of grains to a recipe. Business:

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Ubiquitous Language $recipe->getEstimatedAlcoholByVolumeABV(); Code: We need to be able to calculate an estimated ABV for a recipe. Business:

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Ubiquitous Language $facilities = new StorageFacilities(); // from container $storage = $facilities->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.

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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 = new HopQuantity(“Simcoe”,”12%AA”,”.2oz per gallon”); Business:

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$recipe->dryHop($hop); $recipe->addIngredient($hop); $recipe->addToBoil($hop); $recipe->addToBoilKettle($hop); $recipe->addToBoiler($hop); $recipe->addFirstWortHop($hop); $recipe->addToFermenter($hop);

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$hop = (new HopsSupplier(…))->findOneByName(‘Simcoe’); $catalog = new RecipeCatalog(…); $recipe = $catalog->findOneRecipeByName(‘iPHPA’); $recipe->addDryHop($hop, new DryHopSchedule(‘7 Days’)); $brewers = new Brewers(…); $brewer = $brewers->findOneByUsername(‘cassell’); $brewSession = new BrewSession($brewer, $recipe, new Datetime()); $brewSession->dryHopsWereAdded($hop, new Datetime());

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$hop = (new HopsSupplierRepository(…))->findOneByName(‘Simcoe’); $catalog = new RecipeCatalogRepository(…); $recipe = $catalog->findOneRecipeByName(‘iPHPA’); $recipe->addDryHop($hop, new DryHopSchedule(‘7 Days’)); $brewers = new BrewersRepository(…); $brewer = $brewers->findOneByUsername(‘cassell’); $brewSession = new BrewSession($brewer, $recipe, new Datetime()); $brewSession->dryHopsWereAdded($hop, new Datetime());

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CRUD/MUD DDD Users Brewers String RecipeName Integer IBU Float(7,3) AlphaAcid Array of ORM Objects GrainBill BeerInventoryRepositoryInterface Menu

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[…], 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.

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DDD BALL OF MUD/CRUD Correctness ✓ Testability Usability Maintainability Modiﬁability

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The Brewer, designed and engraved in the Sixteenth Century, by Jost Amman.

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Inventory Marketing Finance Production “Hop”

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Quantity at a Location Flavor Expenditure Ingredient “Hop”

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Bounded Contexts

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Inventory Recipes Brewhouse

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Slide: Vaughn Vernon

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Inventory Recipes Brewhouse

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Inventory Recipes Brewhouse

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Message Inventory Recipes Brewhouse

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Domain Event Inventory Recipes Brewhouse

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Personas

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adaptivepath.com

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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.

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https://blog.intercom.io/using-job-stories-design-features-ui-ux/

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7 Dirty Words When Meeting With a Domain Expert 1.Session 2.Repository 3.Abstract 4.Interface 5.Class 6.Database 7.Foreign Key

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User Research

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Photo: Mathias Verraes

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Command Actor Model Domain Event View Whatever

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Domain Event • Something that happens in the software. • Past Tense

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Domain Event • Beer Was Brewed • Grain Was Added • Hops Were Added • Brewer Changed Email Address

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https://bit.ly/2LL1Xib

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Command Actor Model Domain Event

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Command • The action that precipitates the event • Written in Present Tense

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Command • Start Brewing Session • Add Grain to Recipe • Add Hops To Fermenter • Change Email Address

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Command Actor Model Domain Event

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Model • Command is acted upon this thing • Might Include Supporting Models

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Model • Recipe • Ingredient • Brewer

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Command Actor Model Domain Event

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Actor • Who did it? • If you only have one user you might not need this

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Water proﬁles change daily

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Command Actor Model Domain Event

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Source: Jeff Patton

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business origami

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Jess McMullin Business Origami

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Jess McMullin Business Origami

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Sean Jalleh

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DDD BALL OF MUD/CRUD Correctness ✓✓ Testability Usability ✓ Maintainability Modiﬁability

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Domain Model

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Domain Objects Value Objects Domain Events Entities Aggregates

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Value Object No Identity (Only Values) *Immutable 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

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OBJECTS FOR ALL THE THINGS

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Value Objects

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Email Address Recipe Name Date We Brewed On Weight Temperature Value Objects

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Value Objects Email Address Recipe Name Date We Brewed On Weight Temperature Ubiquitous Language

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Value Objects EmailAddress RecipeName BrewedOn Pounds DegreesFahrenheit Email Address Recipe Name Date We Brewed On Weight Temperature

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Plain Old PHP Objects (POPOs) Value Objects

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Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md Value Objects

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Passed in by Reference / Pointer

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Spooky Action at a Distance

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Mutable objects depend on state.

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Mutable objects depend on time.

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$mutable->function(a,b,c) { global $time; //… } $immutable->function(a,b,c) { //… }

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$mutable->getValue() { global $time; return $value($time); } $immutable->getValue() { return $value; }

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My pragmatic summary: A large fraction of the flaws in software development are due to programmers not fully understanding all the possible states their code may execute in.

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Immutability

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Function

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value Mutable

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42 Mutated

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value Immutable

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value Immutable

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value Immutable

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value Immutable

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Mutable Immutable Read-Only After Creation Read & Write

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They are not dependencies that you inject. Value Objects

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IMMUTABLE AND ALWAYS VALID Value Objects

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Value Objects

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“Gateway Drug to Test Driven Development” Value Objects

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“Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS

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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

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Only depend on scalars or other value objects. Value Objects

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RecipeName Example

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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.

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BrewedOn Example

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Pounds Example

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0); // false var_dump(-0.0 < 0); // false var_dump(-0.0 === 0.0); // true (float) var_dump(-0.0 === 0); // false (int) var_dump(-0.0 == false); // true (bool) var_dump(-0.0 == null); // true (bool) var_dump(-0.0 == “”); // true var_dump(-0.0 == "negativezero"); // true (string)

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$poundA->reduceBy($poundB);

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Eliminate Checking Value Objects

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What should be and Immutable Value Object?

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Event

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Event History

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Request

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Response

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Almost Everything

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Natural Language Constructors

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Natural Language Factory Methods

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Static Constructors

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Resist the Urge to Extend

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class Pounds extends FloatValue { //… }

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class EmailAddress extends StringObject { //… }

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Temperature Example

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Composite Value Objects

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Composite Value Objects

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Encoding Business Logic in Value Objects

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Alcohol by Volume

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Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2

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Sugar + Yeast = Alcohol + CO2

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Sugar - Sugar = Alcohol START FINISH

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Sugar - Sugar = Alcohol START FINISH Volume Volume

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Hydrometer

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learntomoonshine.com

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Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2

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Calibration Temperature Minimum Gravity Reading Maximum Gravity Reading

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Как тебе такое, Илон Маск?

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DDD CRUD/MUD RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?

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DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓ Usability ✓ Maintainability Modiﬁability

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Domain Entities

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Entities Identiﬁable Have State and are Mutable (Lifecycle) Operate using Value Objects *(Ideally) Storage Agnostic *(Ideally) Never in an Invalid State

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DO AS MUCH AS YOU CAN IN VALUE OBJECTS!

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Doctrine Zend Hydrator *Laravel Eloquent ORM “Storage Agnostic”

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BEHAVIOR FIRST! STORAGE SECOND! “Storage Agnostic”

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Single Entity Entities Regular Aggregate Contain Other Entities

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Brewer Grain Hops BeerOnTap Entity Types Regular Aggregate Invoice Recipe BrewSession BeerMenu

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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, …

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SETTERS ARE BAD

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Calling two setters in a row on the same object Missing a Concept?

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Calling two methods in a row on the same object Missing a Concept?

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Passing more than one parameter to a method Missing a Concept?

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Doctrine

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Bounded Contexts

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Inventory Recipes Brewhouse

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Inventory Recipes Brewhouse Recipe\Grain Inventory\Grain Brewing\BrewSession\Grain

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Inventory Recipes Brewhouse

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Inventory Recipes Brewhouse Brewers Supporting Bounded Context

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Mathias Verraes - Mathias Verraes - Emergent Boundaries https://www.youtube.com/watch?v=ECM1rPYxvD4

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• Entities • Manages Child Entities • Transactional Boundary • The Easiest Models to Identify Aggregates

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Aggregates Recipe BrewSession BeerMenu

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Immutable “Entity”

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Immutable Book Mutable Price

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$book->setPrice(16.96); $price = new Price($book,15.00) $price->setAmount(16.96); Mutable Immutable

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$book->setPrice(16.96); $amount = new Amount(16.96, new Currency(‘USD’); $price = new BookPrice($book, $amount); $price->change(new Amount(15.99, new Currency(‘USD’)); Mutable Immutable

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Immutable Collections

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npm install immutable

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</ script> <script> var map1 = Immutable.Map({ a: 1, b: 2, c: 3 }); var map2 = map1.set('b', 50); map1.get('b'); // 2 map2.get('b'); // 50

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Value Object

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“Immutable” Collection of Entities

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$recipe->addGrain() $recipe->removeGrain() $recipe->updateGrain()

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$object->create(x) $object->read(x) $object->update(x) $object->delete(x)

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$object->create(x) { // validate x }

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$object->read(x) { // validate x }

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$object->update(x) { // validate x }

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$object->delete(x) { // validate x }

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Validate Once Not Validating Transitions Easier to Define the Rules Fewer Moving Parts

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Entity’s job is to manage state.

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DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓ Maintainability ✓✓ Modiﬁability ✓

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Task Based User Interface

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Security

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Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates

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Controller Domain Module

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Controller Domain Package

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Controller Domain Framework

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Controller Domain Framework

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Mathias Verraes - Decoupling the Model from the Framework at Laracon EU 2014 https://www.youtube.com/watch?v=QaIGN_cTcc8

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Ruby Midwest 2011 - Keynote: Architecture the Lost Years by Robert Martin https://www.youtube.com/watch?v=WpkDN78P884

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Domain (Business Logic) Application Services Controller Persistence Event/Command Bus Security Templates

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DDD BALL OF MUD/CRUD Correctness ✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modiﬁability ✓

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Domain Events

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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

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BrewSessionWasPlanned

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BrewSessionWasPlanned

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Inventory Recipes Brewhouse

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Domain Event Inventory Recipes Brewhouse

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Domain Event Inventory Recipes Brewhouse

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Inventory Recipes Brewhouse Legacy Context

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Inventory Recipes Brewhouse Legacy Context

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Inventory Recipes Brewhouse Legacy Context

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Inventory Recipes Brewhouse Anticorruption Layer Legacy Context Legacy Code Legacy Services

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DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓ Modiﬁability ✓✓

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Speciﬁcations Repositories Factories Fetch Build/Create Filter/Evaluate Services Do Things

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(EXCEPT CACHING!)

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SPECIFICATION

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Speciﬁcations $spec->isSatisfiedBy($object);

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Example MinimumDiastaticPowerSpecification

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CQRS

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Command Query Responsibility Segregation (Command–query separation)

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Write Read

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Write Model Read Model(s)

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Write Domain Model Read Model(s)

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Write Domain Model Read (Complicated SQL Queries)

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Controller Command Bus Handler Handler Handler

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Controller Command Bus Handler Handler Handler Request

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Controller Command Bus Handler Handler Handler Command

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Controller Command Bus Handler Handler Handler Command

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Controller Command Bus Handler Handler Handler Command

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Controller Command Bus Handler Handler Handler Command

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Controller Command Bus Handler Handler Handler Command Response

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Controller Command Bus Handler Handler Handler Command

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Controller Command Bus Handler Handler Handler Response

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Controller Command Bus Handler Handler Handler Response

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Controller Command Bus Handler Handler Handler Response

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https://gnugat.github.io/ 2016/05/11/towards-cqrs- command-bus.html

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Why Do CQRS?

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Controller Domain Framework

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Controller API (versions?) Console Commands

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Command Bus Command Query Responsibility Segregation

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Write Domain Model Read Model(s)

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DDD BALL OF MUD/CRUD Correctness ✓✓✓ Testability ✓✓ Usability ✓✓ Maintainability ✓✓✓✓ Modiﬁability ✓✓✓

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Event Sourcing

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Event Sourcing • Object Properties are Not Persisted • Events Are Persisted to Append Only Event Storage

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• Avoids Object-relational Impedance Mismatch • Reduces Database Table Counts (Related Tables) • Potentially Reduces Model Counts Event Sourcing

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Slide: Microsoft

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Libraries • https://github.com/eventsaucephp • https://github.com/broadway • https://github.com/prooph • https://github.com/szjani/predaddy

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Recipe Example

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Recipe was created with name “New Recipe” Recipe name was changed to “php[world] IPhpA” 11 pounds of 2-Row Malted Barley was added 2 pounds of Winter Wheat was added 1 pound of Vienna Malt was added 8 gallons of water was added 2 ounces of Centennial Hops for 60 Minutes 1 ounce of Centennial Hop added at whirlpool

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Recipe Example

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Learning More

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homebrewersassociation.org

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DEV BOOK CLUB https://www.youtube.com/user/devbookclub

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https://idddworkshop.com/

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DDDinPHP Google Group http://DDDinPHP.org

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Final Thoughts

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DDD Topics Covered •Ubiquitous Language •Event Storming •Modelling •Value Objects •Entities •Aggregates •Hexagonal Architecture •CQRS •Event Sourcing @alc277 andrewcassell.com