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DDD & CQRS THE BUZZWORD CONFERENCE @lilobase https://lgo.group

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VS DATA-DRIVEN DOMAIN-DRIVEN WHAT DATA ? WHAT BEHAVIOR ?

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VS UPDATE ADDRESS MISTAKE CORRECTION RELOCATION CRUD ARCHITECTURE TASK BASED UI STAND FOR USER INTERACTION USER INTENT IS LOST :-(

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DO YOU WANT TO HAVE AS MUCH ADDED VALUE THAN AN ACCESS DATABASE ?

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WHAT DO THEY NEED ? WELCOME TO SPORTLAND Subscription plan Membership management Revenues from membership Pay-as-you-gym option

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HOW DO WE START ? SubscriptionController UserController DashboardController SessionController MCD CONTROLLERS SAME AS HAVING ANEMIC DOCTRINE ENTITIES

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CreateSubscriptionPlan Subscribe SubscriptionGrossRevenue StartSession ENTITIES USE CASES Subscription Plan Subscription Membership Session YOU DON’T NEED TO HAVE THE FULL CORRECT LISTS, JUST ENOUGH TO GET STARTED HOW DO WE START ?

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THE RULE YAGNI Never write code that is not required to fulfill a use case « »

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IT WAS JUST IN CASE

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ENTITY & AGGREGATE ROOT

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ENTITIES & VALUE OBJECTS DateTime Money BillingInterval ENTITIES VALUE OBJECTS Subscription Membership Session THE DOMAIN IS EXPRESS THROUGH PLAIN OLD PHP OBJECTS CATEGORIZED BETWEEN ENTITIES & VALUE OBJECTS EQUALITY ON IDENTITY, HAS LIFECYCLE EQUALITY ON VALUES, HAS NO LIFECYCLE

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AGGREGATE ROOT MEMBERSHIP SUBSCRIPTION PLAN SUBSCRIBED ACTIVITIES MEMBER ID OPERATIONS CAN ONLY BE PERFORMED THROUGH THE ROOT ENFORCE INTEGRITY REFERENCE TO COLLABORATOR WITH ≠ LIFECYCLE AGGREGATE OBJECT’S SHARE A COMMON LIFECYCLE: THEY CAN BE SAVED & FETCHED AS A WHOLE

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USE CASES COMMAND VS QUERY

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COMMAND VS QUERY COMMAND WRITE, MUTATION QUERY READ EXPRESS INTENT TO PERFORM NEEDED INFORMATIONS TO TAKE A DECISION USE CASES ARE DISCRIMINATED BETWEEN COMMANDS & QUERIES

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LET’S CREATE A COMMAND namespace App\Subscription\Command; class CreateSubscriptionPlanCommand implements Command { public $price; public $name; public $annualDiscount; public $expirationDate; public $includedActivities; public function __construct(/* ... */) { $this->price = $price; $this->name = $name; $this->annualDiscount = $annualDiscount; $this->expirationDate = $expirationDate; $this->includedActivities = $includedActivities; } } A COMMAND IS A SIMPLE DTO IN THE COMMAND NAMESPACE

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AND ITS ASSOCIATED HANDLER namespace App\Subscription\Command; class CreateSubscriptionPlanCommandHandler implements CommandHandler { function __construct(SubscriptionPlanRepository $repository) { $this->repository = $repository; } function handle(CreateSubscriptionPlanCommand $command) { /* ... */ } function listenTo(): string { return CreateSubscriptionPlanCommand::class; } } THE ASSOCIATED COMMAND

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AND ITS ASSOCIATED HANDLER namespace App\Subscription\Command; class CreateSubscriptionPlanCommandHandler implements CommandHandler { function __construct(SubscriptionPlanRepository $repository) { $this->repository = $repository; } function handle(CreateSubscriptionPlanCommand $command) { /* ... */ } function listenTo(): string { return CreateSubscriptionPlanCommand::class; } } COLLABORATOR INTERFACE

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DI / THE HEXAGONE DOMAIN DOMAIN INTERFACE CONCRETE IMPLEMENTATION OF THE DOMAIN INTERFACE TECHNICAL COLLABORATOR

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AND ITS ASSOCIATED HANDLER class CreateSubscriptionPlanCommandHandler implements CommandHandler { function handle(Command $command): CommandResponse { $subscription = new SubscriptionPlan( $command->name, Money::EURO($command->price), $command->annualDiscount, new \DateTime($command->expirationDate), $command->includedActivities ); $this->repository->add($subscription); return CommandResponse::withValue($subscription->id()); } AN AGGREGATE ROOT

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AND ITS ASSOCIATED HANDLER class CreateSubscriptionPlanCommandHandler implements CommandHandler { function handle(Command $command): CommandResponse { $subscription = new SubscriptionPlan( $command->name, Money::EURO($command->price), $command->annualDiscount, new \DateTime($command->expirationDate), $command->includedActivities ); $this->repository->add($subscription); return CommandResponse::withValue($subscription->id()); } PERSISTENCE

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AND ITS ASSOCIATED HANDLER class CreateSubscriptionPlanCommandHandler implements CommandHandler { function handle(Command $command): CommandResponse { $subscription = new SubscriptionPlan( $command->name, Money::EURO($command->price), $command->annualDiscount, new \DateTime($command->expirationDate), $command->includedActivities ); $this->repository->add($subscription); return CommandResponse::withValue($subscription->id()); } ACK/NAK RESPONSE (NO ‘DATA’)

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USING IT $repository = new SubscriptionPlanInMemoryRepository(); $handler = new CreateSubscriptionPlanCommandHandler($repository); $response = $handler->handle( new CreateSubscriptionPlanCommand( 'label', 12, 20, '2018-10-02', ['gym', ‘tennis’] )); //we get the created subscription plan Uuid $response->value();

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CQS THE SHARED REPOSITORY

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CQS COMMAND QUERY HANDLER HANDLER REPOSITORY INTENT VIEW MODEL

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CQS - THE REPOSITORY REPOSITORY DOMAIN INTERFACE IMPLEMENTATION CAN BE IMPLEMENTED USING DOCTRINE DOMAIN ENTITIES NOT ORM ENTITIES

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CQS REPOSITORY INTERFACE namespace App\Subscription\Domain; use App\Common\DDD\Repository; use Ramsey\Uuid\Uuid; interface SubscriptionPlanRepository extends Repository { public function get(Uuid $id): SubscriptionPlan; public function add(SubscriptionPlan $entity): void; public function delete(Uuid $id): void; public function getAllPlan(): array; public function findActivePlan(): array; } IN THE DOMAIN NAMESPACE

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CQS REPOSITORY INTERFACE namespace App\Subscription\Domain; use App\Common\DDD\Repository; use Ramsey\Uuid\Uuid; interface SubscriptionPlanRepository extends Repository { public function get(Uuid $id): SubscriptionPlan; public function add(SubscriptionPlan $entity): void; public function delete(Uuid $id): void; public function getAllPlan(): SubscriptionPlan[]; public function findActivePlan(): SubscriptionPlan[]; } RETURNS DOMAIN ENTITY

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CQS REPOSITORY INTERFACE namespace App\Subscription\Domain; use App\Common\DDD\Repository; use Ramsey\Uuid\Uuid; interface SubscriptionPlanRepository extends Repository { public function get(Uuid $id): SubscriptionPlan; public function add(SubscriptionPlan $entity): void; public function delete(Uuid $id): void; public function getAllPlan(): array; public function findActivePlan(): array; } WE KEEP THE CONTROL OVER OUR ENTITY ID

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LET’S CREATE A QUERY namespace App\Subscription\Query; use App\Common\DDD\Query; class FindActiveSubscriptionPlansQuery implements Query { } A QUERY IS ALSO A SIMPLE DTO IN THE QUERY NAMESPACE

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AND ITS ASSOCIATED HANDLER namespace App\Subscription\Query; class FindActiveSubscriptionPlansQueryHandler implements QueryHandler { function __construct(SubscriptionPlanRepository $repository) { $this->repository = $repository; } function handle(Query $query): array { /* ... */ } function listenTo(): string { FindActiveSubscriptionPlansQuery::class; } } COLLABORATOR INTERFACE THE ASSOCIATED QUERY

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AND ITS ASSOCIATED HANDLER class FindActiveSubscriptionPlansQueryHandler implements QueryHandler { function handle( FindActiveSubscriptionPlansQuery $query ):SubscriptionPlanViewModel[] { return array_map(function(SubscriptionPlan $plan) { return SubscriptionPlanViewModel::fromEntity($plan); }, $this->repository->findActivePlan()); } } MAP ENTITIES TO VIEW MODEL RETURNS A VIEW MODEL

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THE BUS & MIDDLEWARE

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THE BUS COMMAND HANDLER WHAT IF WE NEED TO APPLY COMMON BEHAVIOR ON ALL COMMAND OR QUERIES ? DISPATCHER BUS MIDDLEWARE MIDDLEWARE LOGGING ERROR HANDLING ACK/NACK

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THE BUS WE HAVE A SEPARATE BUS FOR COMMANDS & QUERIES HANDLER DISPATCHER BUS LOGGING ERRORS HANDLER DISPATCHER BUS LOGGING CACHE WE CAN CONFIGURE SPECIFIC MIDDLEWARE ACK/NACK QUERY VIEWMODEL COMMAND

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LET’S CREATE A MIDDLEWARE class LoggerMiddleware implements CommandBusMiddleware { function __construct( CommandBusMiddleware $next, LoggerInterface $logger ) { $this->next = $next; $this->logger = $logger; } function dispatch(Command $command): CommandResponse { /* ... */ } } NEXT MIDDLEWARE (CAN BE THE DISPATCHER) COLLABORATOR

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LET’S CREATE A MIDDLEWARE class LoggerMiddleware implements CommandBusMiddleware { function dispatch(Command $command): CommandResponse { $startTime = microtime(true); $response = $this->next->dispatch($command); $endTime = microtime(true); $elapsed = $endTime - $startTime; $message = 'Command '.get_class($command).' took: '.$elapsed; $this->logger->info($message); return $response; } } BEFORE THE COMMAND IS EXECUTED

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LET’S CREATE A MIDDLEWARE class LoggerMiddleware implements CommandBusMiddleware { function dispatch(Command $command): CommandResponse { $startTime = microtime(true); $response = $this->next->dispatch($command); $endTime = microtime(true); $elapsed = $endTime - $startTime; $message = 'Command '.get_class($command).' took: '.$elapsed; $this->logger->info($message); return $response; } } AFTER THE COMMAND EXECUTION

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LET’S CREATE A MIDDLEWARE class LoggerMiddleware implements CommandBusMiddleware { function dispatch(Command $command): CommandResponse { $startTime = microtime(true); $response = $this->next->dispatch($command); $endTime = microtime(true); $elapsed = $endTime - $startTime; $message = 'Command '.get_class($command).' took: '.$elapsed; $this->logger->info($message); return $response; } } RETURNS THE COMMAND RESPONSE

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AND NOW THE DISPATCHER class CommandBusDispatcher implements CommandBusMiddleware { public function __construct(iterable $handlers) { foreach ($handlers as $handler) { $this->handlers[$handler->listenTo()] = $handler; } } public function dispatch(Command $command): CommandResponse { $commandClass = get_class($command); $handler = $this->handlers[$commandClass]; if($handler == null) throw new \LogicException( "Handler for command $commandClass not found"); return $handler->handle($command); } } WE REGISTER EACH HANDLER WITH ITS ASSOCIATED COMMAND

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AND NOW THE DISPATCHER class CommandBusDispatcher implements CommandBusMiddleware { public function __construct(iterable $handlers) { foreach ($handlers as $handler) { $this->handlers[$handler->listenTo()] = $handler; } } public function dispatch(Command $command): CommandResponse { $commandClass = get_class($command); $handler = $this->handlers[$commandClass]; if($handler == null) throw new \LogicException( "Handler for command $commandClass not found"); return $handler->handle($command); } } WE DISPATCH THE RECEIVED COMMAND TO ITS HANDLER

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FINALLY, THE BUS class CommandBusFactory { static function build( iterable $handler Logger $logger ): CommandBus { return new LoggerBusMiddleware( new CommandBusDispatcher($handler), $logger); } }

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USING THE SF DIC services: # ... App\Common\Infrastructure\CommandBus: factory: 'App\Service\CommandBusFactory:build' arguments: [!tagged ddd.command_handler, @logger] lazy: true src/Kernel.php protected function build(ContainerBuilder $container) { $container ->registerForAutoconfiguration(CommandHandler::class) ->addTag(‘ddd.command_handler’); } config/services.yaml

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USAGE /** * Class PaymentResource * @Route(“/plans”) */ class PlansResource { public function __construct( CommandBus $commandBus, SerializeInterface $serializer ) { $this->commandBus = $commandBus; $this->serializer = $serializer; } /** * @Route("/", methods={POST}) */ public function create(Request $request) { /* ... */ WE RECEIVE THE COMMAND BUS FROM THE DIC

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USAGE /** * Class PaymentResource * @Route(“/plans”) */ class PlansResource { /** * @Route("/", methods={POST}) */ public function create(Request $request) { $command = $this->serializer->deserialize( $request->getContent(), CreateSubscriptionPlanCommand::class, 'json' ); $response = $this->commandBus->dispatch($command); return Response::create($response->value(), 201); } } FIRST WE GET THE COMMAND

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USAGE /** * Class PaymentResource * @Route(“/plans”) */ class PlansResource { /** * @Route("/", methods={POST}) */ public function create(Request $request) { $command = $this->serializer->deserialize( $request->getContent(), CreateSubscriptionPlanCommand::class, 'json' ); $response = $this->commandBus->dispatch($command); return Response::create($response->value(), 201); } } THEN WE DISPATCH IT

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USAGE /** * Class PaymentResource * @Route(“/plans”) */ class PlansResource { /** * @Route("/", methods={POST}) */ public function create(Request $request) { $command = $this->serializer->deserialize( $request->getContent(), CreateSubscriptionPlanCommand::class, 'json' ); $response = $this->commandBus->dispatch($command); return Response::create($response->value(), 201); } } WE SEND THE RESULT

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THE BUS COMMAND HANDLER A GREAT PLACE TO PUT A TRANSACTIONAL MIDDLEWARE DISPATCHER BUS MIDDLEWARE TRANSACTION ACK/NACK

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DOCTRINE FLUSH MIDDLEWARE class DoctrineFlushBusMiddleware { function __construct(CommandBus $next, 
 EntityManagerInterface $entityManager) { $this->next = $next; $this->entityManager = $entityManager; } function dispatch(Command $command): CommandResponse { $this->entityManager->getConnection()->beginTransaction(); try{ $commandResponse = $this->next->dispatch($command); $this->entityManager->flush(); $this->entityManager->getConnection()->commit(); }catch(){ $this->entityManager->getConnection()->rollBack(); } return $commandResponse; } } AUTO FLUSH AFTER COMMAND EXECUTION

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DOMAIN EVENT BUSINESS SIDE-EFFECTS

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DOMAIN EVENT COMMAND HANDLER ACK/NACK DOMAIN EVENTS REPRESENT A FACT AND NOT AN INTENT LIKE A COMMAND

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THE RULE LOCAL EVENT ≠ GLOBAL These events are not for a global messaging bus like kafka « »

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WHAT IS AN EVENT ? namespace App\Membership\Domain; class MemberJoined implements Event { public $newMemberId; public $choosenPlanId; public function __construct( Uuid $newMemberId, Uuid $choosenPlanId ) { $this->newMemberId = $newMemberId; $this->choosenPlanId = $choosenPlanId; } } IT IS ALSO A DTO ! IN THE DOMAIN NAMESPACE

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ADDING EVENTS TO OUR HANDLERS class JoinMembershipCommandHandler implements CommandHandler { public function handle(Command $command): CommandResponse { /* ... */ return CommandResponse::withValue( $membership->id(), new MemberJoined($membership->id(), $plan->id()) ); } WE RETURN AN EVENT static function withValue($value, Event... $events): CommandResponse { return new CommandResponse($value, $events); } WITHVALUE SIGNATURE

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EVENT HANDLERS class SendWelcomeMailOnMemberJoined implements EventHandler { function __construct( Mailer $mailer, SubscriptionPlanRepository $planRepository, MemberRepository $memberRepository ) { $this->mailer = $mailer; $this->planRepository = $planRepository; $this->memberRepository = $memberRepository; } function handle(MemberJoined $event): void { /* ... */ } function listenTo(): string { return MemberJoined::class; } } THE ASSOCIATED EVENT COLLABORATORS

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EVENT HANDLERS class SendWelcomeMailOnMemberJoined implements EventHandler { function __construct(/* ... */) {} function handle(MemberJoined $event): void { $member = $this->memberRepository->get($event->memberId); $plan = $this->memberRepository->get($event->choosenPlanId); $message = “Hello .$member->firstname(),welcome in SportLand. We hope you'll enjoy your $plan->name() subscription”; $mailer->send($member->email(), $message); } function listenTo(): string {} } RETURNS VOID THEY ARE A GREAT PLACE TO EXPRESS “BUSINESS SIDE EFFECTS”

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EVENT HANDLING COMMAND HANDLER UNLIKE COMMANDS OR QUERIES, EVENTS CAN HAVE MULTIPLE HANDLERS DISPATCHER BUS EVENTS MIDDLEWARE MIDDLEWARE EVENT ACK/NACK EVENT DISPATCHER EVENT HANDLER EVENT HANDLER EVENT HANDLER

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EVENT DISPATCHER MIDDLEWARE class EventDispatcherBusMiddleware implements CommandBusMiddleware { function __construct(CommandBus $next, EventBus $eventBus) { $this->bus = $bus; $this->eventBus = $eventBus; } public function dispatch(Command $command): CommandResponse { $commandResponse = $this->bus->dispatch($command); if($commandResponse->hasEvents()) { foreach ($commandResponse->events() as $event) { $this->eventBus->dispatch($event); } } return $commandResponse; } } ITS ALSO A BUS ! A HANDLER CAN EMIT MULTIPLE EVENTS

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AND THE EVENT DISPATCHER class EventBus implements \App\Common\DDD\EventBus { public function __construct(iterable $handlers) { foreach ($handlers as $handler) { $this->handlers[] = $handler; } } public function dispatch(Event $event): void { $eventClass = get_class($event); $matchingHandlers = array_filter($this->handlers, function($handler) use ($eventClass) { return $handler->listenTo() === $eventClass; }); foreach ($matchingHandlers as $handler) { $handler->handle($event); } } } WE CAN ASK THE SF DIC FOR CLASS THAT IMPLEMENTS EVENTHANDLER

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AND THE EVENT DISPATCHER class EventBus implements \App\Common\DDD\EventBus { public function __construct(iterable $handlers) { foreach ($handlers as $handler) { $this->handlers[] = $handler; } } public function dispatch(Event $event): void { $eventClass = get_class($event); $matchingHandlers = array_filter($this->handlers, function($handler) use ($eventClass) { return $handler->listenTo() === $eventClass; }); foreach ($matchingHandlers as $handler) { $handler->handle($event); } } } AN EVENT CAN HAVE MULTIPLE HANDLERS

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PROJECTION & SOME CQRS

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PROJECTION COMMAND HANDLER DISPATCHER BUS EVENTS MIDDLEWARE MIDDLEWARE ACK/NACK EVENT DISPATCHER EVENT HANDLER AN EVENT HANDLER CAN UPDATE ANOTHER DATASTORE

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PROJECTION class UpdateReferralProgramOnMemberJoined implements EventHandler { function handle(MemberJoined $event): void { $findReferrerQuery = $this->connection->prepare(" SELECT rt1.referral_id r1, rt2.referral_id r2 FROM referral rt1 LEFT JOIN referral rt2 ON r1.referral_id = r2.id WHERE r1.id = :referrer "); /* then we update the corresponding referrer counter */ } public function listenTo(): string { return MemberJoined::class; } }

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PROJECTION COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER DATABASE REPOSITORY MEMBERSHIP REFERRAL YOU CAN UPDATE ANOTHER TABLE IN THE SAME DATABASE PROJECTOR SINGLE SOURCE OF TRUTH

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PROJECTION COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER DATABASE REPOSITORY MEMBERSHIP LIKE ANONYMIZED STATS (FREE RGPD COMPLIANCE) REFERRAL PROJECTOR

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PROJECTION COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY MEMBERSHIP YOU CAN UPDATE DATA IN ANOTHER DATABASE PROJECTOR

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PROJECTION COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY MEMBERSHIP LIKE A LEGACY DATABASE (FREE LEGACY MIGRATION) PROJECTOR

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PROJECTION COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY MEMBERSHIP OR IN COMPLETELY DIFFERENT DATASTORE (GIS, SEARCH, …) PROJECTOR

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PROJECTIONS COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY AND YOU CAN MIX THEM PROJECTOR PROJECTOR PROJECTOR

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CQRS COMMAND QUERY RESPONSABILITY SEGREGATION

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CQS COMMAND QUERY HANDLER HANDLER REPOSITORY INTENT VIEW MODEL

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CRQS COMMAND QUERY HANDLER HANDLER REPOSITORY INTENT VIEW MODEL

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CQRS REPOSITORY INTERFACE namespace App\Subscription\Domain; use App\Common\DDD\Repository; use Ramsey\Uuid\Uuid; interface SubscriptionPlanRepository extends Repository { public function get(Uuid $id): SubscriptionPlan; public function add(SubscriptionPlan $entity): void; public function delete(Uuid $id): void; } NO MORE SPECIFIC QUERY METHOD IT SHOULD LOOK LIKE A MAP INTERFACE

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CQRS REPOSITORY class BasketDoctrineRepository implements Repository { public function __construct(EntityManagerInterface $entityManager) { $this->doctrineEntityManager = $entityManager; } public function get(Uuid $uuid): Basket { $doctrineEntity = $this->doctrineEntityManager ->getRepository(BasketDoctrineEntity::class) ->find($uuid); if($doctrineEntity == null) throw new EntityNotFoundException(); return Basket::mapFromDoctrine($doctrineEntity); } public function add(Basket $entity): void { $this->doctrineEntityManager ->merge(BasketDoctrineEntity::mapFromPayment($entity)); }

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CQRS REPOSITORY class BasketDoctrineRepository implements Repository { public function __construct(EntityManagerInterface $entityManager) { $this->doctrineEntityManager = $entityManager; } public function get(Uuid $uuid): Basket { $doctrineEntity = $this->doctrineEntityManager ->getRepository(BasketDoctrineEntity::class) ->find($uuid); if($doctrineEntity == null) throw new EntityNotFoundException(); return Basket::mapFromDoctrine($doctrineEntity); } public function add(Basket $entity): void { $this->doctrineEntityManager ->merge(BasketDoctrineEntity::mapFromPayment($entity)); } IMPLEMENTED WITH A TRAIT

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CQRS REPOSITORY class BasketDoctrineRepository implements Repository { public function __construct(EntityManagerInterface $entityManager) { $this->doctrineEntityManager = $entityManager; } public function get(Uuid $uuid): Basket { $doctrineEntity = $this->doctrineEntityManager ->getRepository(BasketDoctrineEntity::class) ->find($uuid); if($doctrineEntity == null) throw new EntityNotFoundException(); return Basket::mapFromDoctrine($doctrineEntity); } public function add(Basket $entity): void { $this->doctrineEntityManager ->merge(BasketDoctrineEntity::mapFromPayment($entity)); } IMPLEMENTED WITH A TRAIT

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CRQS - THE QUERY COMMAND QUERY HANDLER HANDLER REPOSITORY INTENT VIEW MODEL

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A QUERY class FindActiveSubscriptionPlansQueryHandler implements QueryHandler { private $connection; public function __construct(EntityManager $connection) { $this->connection = $connection; } public function handle(Query $query): array { $query = $this->connection->createQuery(" SELECT NEW SubscriptionViewModel(s.name, s.price) FROM Subscription s "); return $query->getResult(); } public function listenTo(): string { FindAllActiveSubscriptionPlansQuery::class; } } WE ASK FOR A DIRECT CONNEXION TO THE DATASTORE

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A QUERY class FindActiveSubscriptionPlansQueryHandler implements QueryHandler { private $connection; public function __construct(EntityManager $connection) { $this->connection = $connection; } public function handle(Query $query): array { $query = $this->connection->createQuery(" SELECT NEW SubscriptionViewModel(s.name, s.price) FROM Subscription s "); return $query->getResult(); } public function listenTo(): string { FindAllActiveSubscriptionPlansQuery::class; } } WE EXECUTE THE QUERY IN THE HANDLER BODY

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THE BIG PICTURE COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY YOU CAN TAKE YOUR DATA FROM THE MOST ADEQUATE STORAGE PROJECTOR PROJECTOR PROJECTOR QUERY HANDLER BUS VIEWMODEL

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SCALING FREE SCALING QUERY HANDLER BUS VIEWMODEL QUERY HANDLER BUS VIEWMODEL QUERY HANDLER BUS VIEWMODEL

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EVENT SOURCING AT LAST…

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OUR AGGREGATE RETURNS EVENTS class Basket implements AggregateRoot { use BasketEventApplier; public function addProduct(Product $product) { $event = new ProductAdded($product); return [ $this->apply($event), $event ]; } } WE BUILD THE CORRESPONDING EVENT

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OUR AGGREGATE RETURNS EVENTS class Basket implements AggregateRoot { use BasketEventApplier; public function addProduct(Product $product) { $event = new ProductAdded($product); return [ $this->apply($event), $event ]; } } WE APPLY IT

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OUR AGGREGATE RETURNS EVENTS class Basket implements AggregateRoot { use BasketEventApplier; public function addProduct(Product $product) { $event = new ProductAdded($product); return [ $this->apply($event), $event ]; } } THEN WE RETURN A TUPLE

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trait BasketEventApplier { private function productAdded(ProductAdded $event) { $instance = $this->createInstance($this); $instance->products[] = new BasketProduct($event); return $instance; } public function apply($event) { $applier = $this->eventMap[get_class($event)]; return $this->$applier($event); } private $eventMap = [ ProductAdded::class => 'productAdded' ]; } THE EVENT APPLIER

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trait BasketEventApplier { private function productAdded(ProductAdded $event) { $instance = $this->createInstance($this); $instance->products[] = new BasketProduct($event); return $instance; } public function apply($event) { $applier = $this->eventMap[get_class($event)]; return $this->$applier($event); } private $eventMap = [ ProductAdded::class => 'productAdded' ]; } THE EVENT APPLIER WE BUILD THE CORRESPONDING STATE FROM EACH EVENT

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EVENT LIFECYCLE COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY EVENTS ARE PERSISTED, NOT THE AGGREGATE STATE PROJECTOR

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ES REPOSITORY INTERFACE namespace App\Subscription\Domain; use App\Common\DDD\Repository; use Ramsey\Uuid\Uuid; interface SubscriptionPlanRepository extends Repository { public function get(Uuid $id): SubscriptionPlan; } NO MORE SAVE METHODS

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ES REPOSITORY INTERFACE class BasketRepository { public function get(Uuid $id) { $events = $this->getEventsByAggregate($id); $instance = new Basket(); foreach ($events as $event){ [$instance, $void] = $instance->apply($events); }; return $instance; } private function getEventsByAggregate(Uuid $id) { $stmt = $this->connection->prepare( "SELECT payload FROM events WHERE aggregate_type = 'BASKET' AND aggregate_id = :id ORDER BY timestamp"); $stmt->execute(['id' => $id->toString()]); $results = $stmt->fetchAll(FetchMode::COLUMN); return array_map(function($result) { unserialize($result['payload']); }, $results); }

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ES REPOSITORY INTERFACE class BasketRepository { public function get(Uuid $id) { $events = $this->getEventsByAggregate($id); $instance = new Basket(); foreach ($events as $event){ [$instance, $void] = $instance->apply($events); }; return $instance; } private function getEventsByAggregate(Uuid $id) { $stmt = $this->connection->prepare( "SELECT payload FROM events WHERE aggregate_type = 'BASKET' AND aggregate_id = :id ORDER BY timestamp"); $stmt->execute(['id' => $id->toString()]); $results = $stmt->fetchAll(FetchMode::COLUMN); return array_map(function($result) { unserialize($result['payload']); }, $results); }

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ES HANDLER class AddProductToBasketCommandHandler implements CommandHandler { public function handle(Command $command): CommandResponse { $basket = $this->repository->get($command->basketId); [$instance, $events] = $basket->addProduct($command->product); return CommandResponse::withValue($instance->id(), $events); }

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THE BIG PICTURE COMMAND HANDLER BUS ACK/NACK EVENT DISPATCHER REPOSITORY PROJECTOR PROJECTOR QUERY HANDLER BUS VIEWMODEL EVENT STORE EVENTS AS A SOURCE OF TRUTH WE CAN CREATE NEW PROJECTION ON DEMAND

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THE RULE CHEF INSTEAD OF COOKBOOK USER We tend to get sidetracked by tools when we should really be thinking about what our tools are supposed to achieve. Chefs instead of recipe book user « » @_edejong

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THANKS ! @LILOBASE et merci à Stéphane Pailha pour son aide dans la préparation de ce talk

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BONUS

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THE LEGACY Can you connect the new membership
 system to our current in house CRM ? BY THE WAY « »

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THIS ? IT’S JUST BECAUSE WE NEEDED TO TALK WITH OUR LEGACY SYSTEM

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ANTI-CORRUPTION LAYER GREENFIELD ACL BROWNFIELD OLD, LEGACY API NEW, CLEAN API YOU MAY NEED A DEDICATED DATABASE