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From CRUD to Hexagonal & DDD “How Meetic saved its codebase” Icons made by Icongeek26, Freepik from www.flaticon.com Jean-Marie Lamodière - Backend tech lead @jmlamodiere

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stackshare.io/meetic @meetictech microservice calls Kafka messages production deployments 3 500 000 000 250 000 000 25 / day

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Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018

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WHY ? n-tiers architecture Presentation (Apps) Presentation Business logic Data access

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But… Monolithic Rest API = new Legacy v2 Icons made by Freepik from www.flaticon.com

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What’s wrong ? We use a modern web framework ! We follow its best practices ! Icons made by Freepik from www.flaticon.com

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WHY ? MVC Framework = CRUD Create Read Update Delete = Database mindset Icons made by Smashicon from www.flaticon.com

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WHY ? MVC Framework = CRUD Typical tutorial : 1. Generate entities + getters + setters 2. Generate Database 3. Expose as REST (or web )

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WHY ? MVC Framework = CRUD N-tiers architecture Presentation Business logic Data access Framework focus Framework focus ...YOLO ! Icons made by Freepik, Smashicon from www.flaticon.com

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WHY ? Tests… with code coverage in mind Complex Class Icons made by Pause08, Freepik from www.flaticon.com = No refactoring Test coupled with internal details + 100%

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What is a useful test ? How to code business complexity ? Icons made by Freepik from www.flaticon.com

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Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018

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WHY ? Let’s try buzzwords ! Test Driven Development Behaviour Driven Development Command Bus Hexagonal architecture Domain Driven Design Command Query Separation Icons made by Roundicons from www.flaticon.com Microservices

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WHY ? 3 years later... ● Inconsistant code designs ● Differing opinions amongst developers Fewer libraries! More libraries! Get sh*t done! Refactor everything! Fewer libraries! More libraries! Refactor everything!

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Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018

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WHY ? Evangelism Pro-tips ● Lead by example Pull Requests, Pair Programming ● Organize debates Teach, show code, vote ● Code example as documentation ● Use (anti-)pattern names

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Hexagonal Architecture = Ports & Adapters Dr. Alistair Cockburn - 2005 Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips

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WHY ?What is “Decoupling” ? Low coupling High cohesion “Allow unrelated things to change independently” Icons made by Roundicons from www.flaticon.com

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WHY ?Hexagonal architecture Low coupling High cohesion “Decoupling business and technical choices” Icons made by Roundicons from www.flaticon.com

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WHY ?Hexagonal architecture “Techno agnostic domain” Infrastructure ● Framework (+ version) ● Libraries (ORM, http client) ● Database ● REST, SOAP, Command line ? Domain (Business logic)

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WHY ? Where to put my code ? Infrastructure Framework, libraries, techno Domain (Business logic) Icons made by Icongeek26 from www.flaticon.com Product Owner Business expert Architect Dev, Ops (Who decides ?)

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WHY ?Domain inside hexagon RepositoryInterface Entity No framework Icons made by Freepik from www.flaticon.com /Domain MemberRepository Member Screaming architecture

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WHY ? Port = simplest interface meeting use-case needs UseCase RepositoryInterface Entity Start inside hexagone, free your mind from infrastructure No framework Icons made by Freepik from www.flaticon.com

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WHY ? Port = simplest interface meeting use-case needs Icons made by Roundicons, Freepik from www.flaticon.com repo.persist(member).flush (framework details) repo.add(member) repo.get(id) A repository can be seen as a list

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WHY ? Port = simplest interface meeting use-case needs Icons made by Roundicons, Freepik from www.flaticon.com Intention revealing interface getInactiveMembers() getDefaultChoices(gender) increaseCounter()

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WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity MysqlRepository HttpRepository No framework Framework welcome Icons made by Freepik from www.flaticon.com TestRepository

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WHY ? Adapter = techno-specific “driver” MysqlRepository Icons made by Freepik from www.flaticon.com /Domain MemberRepository Member /Infrastructure MysqlMemberRepo... Framework welcome

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WHY ? MysqlMemberRepository implements MemberRepositoryInterface { getInactiveMembers() {...} } Adapter = techno-specific “driver” Techno name Icons made by Freepik from www.flaticon.com

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WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity MysqlRepository @Throws UserNotFound Icons made by Freepik from www.flaticon.com Convert infra exceptions to domain exceptions

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WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity AggregatorRepository MysqlDao* CacheDecoratorDao HttpDao *Data Access Object (No impact here) Icons made by Freepik from www.flaticon.com (Complex infra)

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WHY ? Difference with n-tiers architecture Service MysqlDao1* Dto1* Dao2Interface *Data Access Object *Data Transfert Object CacheDecoratorDao2 HttpDao2 Dto2 (Aware of 2 Dao) (Mimic database structure)

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WHY ? Port & Adapters : entrypoints UseCase RepositoryInterface Entity RestController Test CliController No framework Framework welcome Icons made by Freepik from www.flaticon.com

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RestController Framework welcome Icons made by Freepik from www.flaticon.com /Infrastructure /Symfony MemberController MemberSerializer WHY ? Port & Adapters : entrypoints

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WHY ? Ex. of adapter refacto @Meetic Symfony 2 Database Database Oracle Icons made by Freepik from www.flaticon.com Symfony 4 External REST API Config files PostgreSQL

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WHY ?Layers inside hexagone UseCase RepositoryInterface Entity Icons made by Freepik from www.flaticon.com Application Use cases (do, get…) Domain Modeling business reality (Use case agnostic)

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Command Query Separation Command (do) : produces an effect Query (get) : gets data, no state change Same as “Query” vs. “Mutation” in GraphQL Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips

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WHY ? Command / Query Separation RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com Query Handler Command Handler

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WHY ? Command / Query Separation /Application /Command RegisterMember RegisterMemberHandler /Query GetNewMembers GetNewMembersHandler /Domain MemberRepository Member

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WHY ? Command / Query Separation Command, Query ● simple DTO ● user intention ● primitive values /Application /Command RegisterMember RegisterMemberHandler /Query GetNewMembers GetNewMembersHandler

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WHY ? Steps 1. Infrastructure\Controller Converts HTTP request to Command/Query and call Handler 2. Application\CommandHandler Apply logic, act on Entity through Repository 3. Infrastructure\Controller Send HTTP response

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WHY ? Command / Query Separation Command Handler RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com Query Handler DaoInterface DTO (with validation) (no logic, readonly) Same database (≠ CQRS)

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WHY ? Command / Query Separation /Application /Command RegisterMember RegisterMemberHandler /Query GetContactPictures GetContactPicturesHandler /Domain MemberRepository Member /Read ContactDao ContactPicture

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WHY ? Command / Query Separation Create custom Read DAO only when it simplifies code Ex : custom DTO with less fields

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Domain Driven Design Eric Evans - 2004 Icons made by Icongeek26, Freepik from www.flaticon.com Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips

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WHY ? Domain Driven Design ● Talk with domain experts ● Use domain words in your code ● Focus on events instead of data Icons made by Icongeek26 from www.flaticon.com

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WHY ? Domain Driven Design Make domain logic explicit

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WHY ? Before DDD : fake entities... Anemic domain model Temporal coupling memberEntity .setStatus(“active”) .setActivationDate(now) .setCanTalk(true) Icons made by Roundicons from www.flaticon.com Feature envy

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WHY ? Same (anti)patterns with REST PUT /member/123 {“status”: “active”, “activDate”:”now”“canTalk”:true} Icons made by Roundicons, Freepik from www.flaticon.com POST /member/123 {“action”: “activate”} Logic on caller = feature envy POST /member/123/activate

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WHY ? DDD Entity Rich domain model Icons made by Roundicons from www.flaticon.com memberEntity .activate() ● State always valid (check invariants) ● Explicit mutators ● Emit domain events

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WHY ? Before DDD : primitive types only... Icons made by Roundicons from www.flaticon.com Primitive obsession productEntity .setPriceAmount(20.50) .setCurrenty(“EUR”) (same concern)

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WHY ? DDD Value Object price = new Price(20.50, “EUR”) productEntity .setPrice(price) ● Explicit ● Immutable ● Valid

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WHY ? DDD Value Object @ Meetic age = new Age(23) … = age .toSearchBirthdayMax() ● Factorize validation ● Factorize features Must be >= 18

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Testing strategy Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips Icons made by Freepik from www.flaticon.com

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WHY ? Inside hexagon: unit tests Command Handler RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com ● Mock Infra only ● Don’t mock entities / value objects Test Mock

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WHY ? Outside hexagon: integration tests Icons made by Freepik, Smashicons from www.flaticon.com Don’t mock a library API The test should allow refactoring : ● QueryBuilder -> SQL ● Change Http library MysqlRepository Docker mysql HttpRepository Wiremock

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Gotchas ? Pro-Tips ? Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips Icons made by Freepik from www.flaticon.com

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WHY ? Do not stack new layers Lava flow Refacto “vertical” business slices Icons made by Freepik, Pixel Perfect, Roundicons from www.flaticon.com New layer Old layer 1 Old layer 2

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WHY ? Gotchas, Pro-tips ● Hexagon overkill when no domain logic. CRUD / framework magic more suited. ● Start inside hexagon, not with database. Otherwise, infra complexity will leak into domain ● To choose layer => whose decision is it ? Product Owner Business expert Architect Dev, Ops @jmlamodiere Icons made by Icongeek26 from www.flaticon.com Thanks for coming !