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Event sourcing in production Willem-Jan Zijderveld @willemjanz [email protected] joind.in/16227

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Event sourcing

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Short introduction into our domain

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Job Marketing Platform

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Choosing the best channels to find your candidates

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Online Job Marketing

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1. Create a campaign for your target group

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2. You get a recommendation

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3. You can customize your campaign

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Why event sourcing?

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You are throwing away data!

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By only saving last known state

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You don't know the previous state

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You don't know why something changed

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How does event sourcing help?

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Using events to store changes

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Describe with your events what happened

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Describe with your events why something happened

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Use the events to calculate the current state

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Allows you to go back in time

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Helps to understand the flow in your application

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Example: Discarding the customizations

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CRUD

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Keep track if channel was part of recommendation

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Keep track if channel was part of recommendation Remove the non-recommended channels

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Keep track if channel was part of recommendation How about removed channels?

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Keep track if channel was part of recommendation Implement soft-delete

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Keep track if channel was part of recommendation Implement soft-delete for new campaigns

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Event sourcing

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Just rewind

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Just rewind Campaign Created For Target Group Channel Removed From Campaign Channel Added To Campaign Customization Discarded

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Just rewind Campaign Created For Target Group Channel Removed From Campaign Channel Added To Campaign Customization Discarded

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Just rewind Campaign Created For Target Group Channel Removed From Campaign Channel Added To Campaign Customization Discarded

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Just rewind Campaign Created For Target Group Channel Removed From Campaign Channel Added To Campaign Customization Discarded

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How?

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With the help of CQRS and Domain Driven Design

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And the help of Broadway github.com/qandidate-labs/broadway

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Creating a new campaign

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Campaign Event Store Create Campaign For Target Group Campaign Created For Target Group

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Dispatching the command /** @Route("/campaigns", methods={"POST"}) */ public function createCampaignAction(CreateCampaignDto $dto) { $campaignId = Webshop\CampaignId::generate(); $this->commandBus->dispatch(new CreateCampaignForTargetGroup( $campaignId, $this->companyId, $this->accountId, TargetGroup::describe( TargetGroup\JobTitle::fromString($dto->title), TargetGroup\Region::fromId($dto->region), TargetGroup\JobCategory::fromId($dto->jobCategory), TargetGroup\EducationLevel::fromId($dto->educationLevel), TargetGroup\JobLevel::fromId($dto->jobLevel), TargetGroup\Industry::fromId($dto->industry) ) )); return new JsonResponse( ['id' => (string) $campaignId], JsonResponse::HTTP_CREATED ); }

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Dispatching the command /** @Route("/campaigns", methods={"POST"}) */ public function createCampaignAction(CreateCampaignDto $dto) { $campaignId = Webshop\CampaignId::generate(); $this->commandBus->dispatch(new CreateCampaignForTargetGroup( $campaignId, $this->companyId, $this->accountId, TargetGroup::describe( TargetGroup\JobTitle::fromString($dto->title), TargetGroup\Region::fromId($dto->region), TargetGroup\JobCategory::fromId($dto->jobCategory), TargetGroup\EducationLevel::fromId($dto->educationLevel), TargetGroup\JobLevel::fromId($dto->jobLevel), TargetGroup\Industry::fromId($dto->industry) ) )); return new JsonResponse( ['id' => (string) $campaignId], JsonResponse::HTTP_CREATED ); }

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Dispatching the command /** @Route("/campaigns", methods={"POST"}) */ public function createCampaignAction(CreateCampaignDto $dto) { $campaignId = Webshop\CampaignId::generate(); $this->commandBus->dispatch(new CreateCampaignForTargetGroup( $campaignId, $this->companyId, $this->accountId, TargetGroup::describe( TargetGroup\JobTitle::fromString($dto->title), TargetGroup\Region::fromId($dto->region), TargetGroup\JobCategory::fromId($dto->jobCategory), TargetGroup\EducationLevel::fromId($dto->educationLevel), TargetGroup\JobLevel::fromId($dto->jobLevel), TargetGroup\Industry::fromId($dto->industry) ) )); return new JsonResponse( ['id' => (string) $campaignId], JsonResponse::HTTP_CREATED ); }

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Handling the command // CampaignCommandHandler.php public function handleCreateCampaignForTargetGroup( CreateCampaignForTargetGroup $command ) { $campaign = Campaign::createForTargetGroup( $command->getCampaignId(), $command->getCompanyId(), $command->getRecruiterId(), $command->getTargetGroup(), $this->recommender ); $this->campaignRepository->save($campaign); }

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Handling the command // CampaignCommandHandler.php public function handleCreateCampaignForTargetGroup( CreateCampaignForTargetGroup $command ) { $campaign = Campaign::createForTargetGroup( $command->getCampaignId(), $command->getCompanyId(), $command->getRecruiterId(), $command->getTargetGroup(), $this->recommender ); $this->campaignRepository->save($campaign); }

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Handling the command // CampaignCommandHandler.php public function handleCreateCampaignForTargetGroup( CreateCampaignForTargetGroup $command ) { $campaign = Campaign::createForTargetGroup( $command->getCampaignId(), $command->getCompanyId(), $command->getRecruiterId(), $command->getTargetGroup(), $this->recommender ); $this->campaignRepository->save($campaign); }

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Action → Reaction // Campaign.php public static function createForTargetGroup(/* args */) { $campaign = new Campaign(); $campaignChannels = $recommender->recommend(/* args */); $campaign->apply(new CampaignCreatedForTargetGroup( $campaignId, $companyId, $accountId, Channels::fromCollection($campaignChannels), $targetGroup, $campaign->calculateCampaignPrice($campaignChannels), $campaign->calculateEstimatedOutcome($campaignChannels) )); return $campaign; }

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Action → Reaction // Campaign.php public static function createForTargetGroup(/* args */) { $campaign = new Campaign(); $campaignChannels = $recommender->recommend(/* args */); $campaign->apply(new CampaignCreatedForTargetGroup( $campaignId, $companyId, $accountId, Channels::fromCollection($campaignChannels), $targetGroup, $campaign->calculateCampaignPrice($campaignChannels), $campaign->calculateEstimatedOutcome($campaignChannels) )); return $campaign; }

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Action → Reaction // Campaign.php public static function createForTargetGroup(/* args */) { $campaign = new Campaign(); $campaignChannels = $recommender->recommend(/* args */); $campaign->apply(new CampaignCreatedForTargetGroup( $campaignId, $companyId, $accountId, Channels::fromCollection($campaignChannels), $targetGroup, $campaign->calculateCampaignPrice($campaignChannels), $campaign->calculateEstimatedOutcome($campaignChannels) )); return $campaign; }

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Action → Reaction // Campaign.php public static function createForTargetGroup(/* args */) { $campaign = new Campaign(); $campaignChannels = $recommender->recommend(/* args */); $campaign->apply(new CampaignCreatedForTargetGroup( $campaignId, $companyId, $accountId, Channels::fromCollection($campaignChannels), $targetGroup, $campaign->calculateCampaignPrice($campaignChannels), $campaign->calculateEstimatedOutcome($campaignChannels) )); return $campaign; }

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// Broadway: EventSourcedAggregateRoot.php public function apply($event) { $this->handleRecursively($event); $this->playhead++; $this->uncommittedEvents[] = DomainMessage::recordNow( $this->getAggregateRootId(), $this->playhead, new Metadata(), $event ); }

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// Broadway: EventSourcedAggregateRoot.php public function apply($event) { $this->handleRecursively($event); $this->playhead++; $this->uncommittedEvents[] = DomainMessage::recordNow( $this->getAggregateRootId(), $this->playhead, new Metadata(), $event ); }

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Campaign Event Store Create Campaign For Target Group Campaign Created For Target Group

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// Campaign.php protected function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event ) { $this->id = $event->getCampaignId(); $this->channels = $event->getRecommendedChannels()->toArray(); $this->campaignPrice = $event->getCampaignPrice(); $this->estimatedOutcome = $event->getEstimatedOutcome(); $this->targetGroup = $event->getTargetGroup(); $this->setInitialRecommendation( $this->channels, $this->estimatedOutcome, $this->campaignPrice ); }

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// Broadway: EventSourcedAggregateRoot.php public function apply($event) { $this->handleRecursively($event); $this->playhead++; $this->uncommittedEvents[] = DomainMessage::recordNow( $this->getAggregateRootId(), $this->playhead, new Metadata(), $event ); }

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// Broadway: EventSourcedAggregateRoot.php public function apply($event) { $this->handleRecursively($event); $this->playhead++; $this->uncommittedEvents[] = DomainMessage::recordNow( $this->getAggregateRootId(), $this->playhead, new Metadata(), $event ); }

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// Broadway: EventSourcedAggregateRoot.php public function apply($event) { $this->handleRecursively($event); $this->playhead++; $this->uncommittedEvents[] = DomainMessage::recordNow( $this->getAggregateRootId(), $this->playhead, new Metadata(), $event ); }

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Handling the command // CampaignCommandHandler.php public function handleCreateCampaignForTargetGroup( CreateCampaignForTargetGroup $command ) { $campaign = Campaign::createForTargetGroup( $command->getCampaignId(), $command->getCompanyId(), $command->getRecruiterId(), $command->getTargetGroup(), $this->recommender, $this->portfolio, $this->aidaMetricsCalculator ); $this->campaignRepository->save($campaign); }

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Saving the events // Broadway: EventSourcingRepository.php public function save(AggregateRoot $aggregate) { // maybe we can get generics one day.... ;) Assert::isInstanceOf($aggregate, $this->aggregateClass); $eventStream = $aggregate->getUncommittedEvents(); $this->eventStore->append( $aggregate->getAggregateRootId(), $eventStream ); $this->eventBus->publish($eventStream); }

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Saving the events // Broadway: EventSourcingRepository.php public function save(AggregateRoot $aggregate) { // maybe we can get generics one day.... ;) Assert::isInstanceOf($aggregate, $this->aggregateClass); $eventStream = $aggregate->getUncommittedEvents(); $this->eventStore->append( $aggregate->getAggregateRootId(), $eventStream ); $this->eventBus->publish($eventStream); }

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Saving the events // Broadway: EventSourcingRepository.php public function save(AggregateRoot $aggregate) { // maybe we can get generics one day.... ;) Assert::isInstanceOf($aggregate, $this->aggregateClass); $eventStream = $aggregate->getUncommittedEvents(); $this->eventStore->append( $aggregate->getAggregateRootId(), $eventStream ); $this->eventBus->publish($eventStream); }

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It happened in the past

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Append only

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Campaign Event Store Create Campaign For Target Group Campaign Created For Target Group

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How would we load a campaign?

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Campaign Event Store Campaign Created For Target Group

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// Broadway: EventSourcingRepository.php public function load($id) { try { $domainEventStream = $this->eventStore->load($id); return $this->aggregateFactory->create( $this->aggregateClass, $domainEventStream ); } catch (EventStreamNotFoundException $e) { throw AggregateNotFoundException::create($id, $e); } } // Broadway: EventSourcedAggregateRoot.php public function initializeState(DomainEventStreamInterface $stream) { foreach ($stream as $message) { $this->playhead++; $this->handleRecursively($message->getPayload()); } }

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// Broadway: EventSourcingRepository.php public function load($id) { try { $domainEventStream = $this->eventStore->load($id); return $this->aggregateFactory->create( $this->aggregateClass, $domainEventStream ); } catch (EventStreamNotFoundException $e) { throw AggregateNotFoundException::create($id, $e); } } // Broadway: EventSourcedAggregateRoot.php public function initializeState(DomainEventStreamInterface $stream) { foreach ($stream as $message) { $this->playhead++; $this->handleRecursively($message->getPayload()); } }

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// Broadway: EventSourcingRepository.php public function load($id) { try { $domainEventStream = $this->eventStore->load($id); return $this->aggregateFactory->create( $this->aggregateClass, $domainEventStream ); } catch (EventStreamNotFoundException $e) { throw AggregateNotFoundException::create($id, $e); } } // Broadway: EventSourcedAggregateRoot.php public function initializeState(DomainEventStreamInterface $stream) { foreach ($stream as $message) { $this->playhead++; $this->handleRecursively($message->getPayload()); } }

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// Broadway: EventSourcingRepository.php public function load($id) { try { $domainEventStream = $this->eventStore->load($id); return $this->aggregateFactory->create( $this->aggregateClass, $domainEventStream ); } catch (EventStreamNotFoundException $e) { throw AggregateNotFoundException::create($id, $e); } } // Broadway: EventSourcedAggregateRoot.php public function initializeState(DomainEventStreamInterface $stream) { foreach ($stream as $message) { $this->playhead++; $this->handleRecursively($message->getPayload()); } }

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Let's add a channel

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Campaign Event Store Add Channel To Campaign Channel Added To Campaign

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// CampaignCommandHandler.php public function handleAddChannelToCampaignCommand( AddChannelToCampaignCommand $command ) { $channel = $this->portfolio->getById($command->getChannelId()); $campaign = $this->campaignRepository->load( $command->getCampaignId() ); $campaign->addChannel($channel, $this->aidaMetricsCalculator); $this->campaignRepository->save($campaign); }

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// CampaignCommandHandler.php public function handleAddChannelToCampaignCommand( AddChannelToCampaignCommand $command ) { $channel = $this->portfolio->getById($command->getChannelId()); $campaign = $this->campaignRepository->load( $command->getCampaignId() ); $campaign->addChannel($channel, $this->aidaMetricsCalculator); $this->campaignRepository->save($campaign); }

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// CampaignCommandHandler.php public function handleAddChannelToCampaignCommand( AddChannelToCampaignCommand $command ) { $channel = $this->portfolio->getById($command->getChannelId()); $campaign = $this->campaignRepository->load( $command->getCampaignId() ); $campaign->addChannel($channel, $this->aidaMetricsCalculator); $this->campaignRepository->save($campaign); }

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// CampaignCommandHandler.php public function handleAddChannelToCampaignCommand( AddChannelToCampaignCommand $command ) { $channel = $this->portfolio->getById($command->getChannelId()); $campaign = $this->campaignRepository->load( $command->getCampaignId() ); $campaign->addChannel($channel, $this->aidaMetricsCalculator); $this->campaignRepository->save($campaign); }

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// Campaign.php public function addChannel( ChannelInPortfolio $channel, AidaMetricsCalculator $aidaMetricsCalculator ) { $this->guardCannotModifyOrderedCampaign(); $channelInCampaign = new ChannelInCampaign(/* $args */); $channels = array_merge($this->channels, [$channelInCampaign]); $campaignPrice = $this->calculateCampaignPrice($channels); $estimatedOutcome = $this->calculateEstimatedOutcome($channels); $this->apply(new ChannelAddedToCampaign( $this->id, $channelInCampaign, $campaignPrice, $estimatedOutcome )); }

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// Campaign.php public function addChannel( ChannelInPortfolio $channel, AidaMetricsCalculator $aidaMetricsCalculator ) { $this->guardCannotModifyOrderedCampaign(); $channelInCampaign = new ChannelInCampaign(/* $args */); $channels = array_merge($this->channels, [$channelInCampaign]); $campaignPrice = $this->calculateCampaignPrice($channels); $estimatedOutcome = $this->calculateEstimatedOutcome($channels); $this->apply(new ChannelAddedToCampaign( $this->id, $channelInCampaign, $campaignPrice, $estimatedOutcome )); }

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// Campaign.php public function addChannel( ChannelInPortfolio $channel, AidaMetricsCalculator $aidaMetricsCalculator ) { $this->guardCannotModifyOrderedCampaign(); $channelInCampaign = new ChannelInCampaign(/* $args */); $channels = array_merge($this->channels, [$channelInCampaign]); $campaignPrice = $this->calculateCampaignPrice($channels); $estimatedOutcome = $this->calculateEstimatedOutcome($channels); $this->apply(new ChannelAddedToCampaign( $this->id, $channelInCampaign, $campaignPrice, $estimatedOutcome )); }

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// Campaign.php protected function applyChannelAddedToCampaign( ChannelAddedToCampaign $event ) { $this->channels[] = $event->getChannel(); $this->campaignPrice = $event->getCampaignPrice(); $this->estimatedOutcome = $event- >getEstimatedOutcomeOfCampaign(); $this->isCustomized = true; }

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How do we get a listing of the campaigns?

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We'll create a read model

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Campaign Event Store Campaign Created For Target Group

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Campaign Event Store Campaign Created For Target Group Read Model Store

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Campaign Event Store Campaign Created For Target Group Read Model Store MySQL Read Model Store Redis

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Saving the events // Broadway: EventSourcingRepository.php public function save(AggregateRoot $aggregate) { // maybe we can get generics one day.... ;) Assert::isInstanceOf($aggregate, $this->aggregateClass); $eventStream = $aggregate->getUncommittedEvents(); $this->eventStore->append( $aggregate->getAggregateRootId(), $eventStream ); $this->eventBus->publish($eventStream); }

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Creating read models // CampaignOverviewProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event, DomainMessage $message ) { $this->repository->save(new CampaignOverview( $event->getCampaignId(), $event->getCompanyId(), $event->getTargetGroup()->getJobTitle(), $message->getRecordedOn() )); }

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Creating read models // CampaignOverviewProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event, DomainMessage $message ) { $this->repository->save(new CampaignOverview( $event->getCampaignId(), $event->getCompanyId(), $event->getTargetGroup()->getJobTitle(), $message->getRecordedOn() )); }

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Creating read models // CampaignOverviewProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event, DomainMessage $message ) { $this->repository->save(new CampaignOverview( $event->getCampaignId(), $event->getCompanyId(), $event->getTargetGroup()->getJobTitle(), $message->getRecordedOn() )); }

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Creating read models // CampaignDetailsProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event ) { $campaignDetails = new CampaignDetails( $event->getCampaignId(), $event->getRecruiterId(), $event->getTargetGroup(), $event->getCompanyId(), $event->getRecommendedChannels()->toArray() ); $campaignDetails->updatePrice($event->getCampaignPrice()); $campaignDetails->updateEstimatedOutcome( $event->getEstimatedOutcome() ); $this->repository->save($campaignDetails); }

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Creating read models // CampaignDetailsProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event ) { $campaignDetails = new CampaignDetails( $event->getCampaignId(), $event->getRecruiterId(), $event->getTargetGroup(), $event->getCompanyId(), $event->getRecommendedChannels()->toArray() ); $campaignDetails->updatePrice($event->getCampaignPrice()); $campaignDetails->updateEstimatedOutcome( $event->getEstimatedOutcome() ); $this->repository->save($campaignDetails); }

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Creating read models // CampaignDetailsProjector.php public function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event ) { $campaignDetails = new CampaignDetails( $event->getCampaignId(), $event->getRecruiterId(), $event->getTargetGroup(), $event->getCompanyId(), $event->getRecommendedChannels()->toArray() ); $campaignDetails->updatePrice($event->getCampaignPrice()); $campaignDetails->updateEstimatedOutcome( $event->getEstimatedOutcome() ); $this->repository->save($campaignDetails); }

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Using the history to your advantage

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Discard Customizations

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// Campaign.php protected function applyCampaignCreatedForTargetGroup( CampaignCreatedForTargetGroup $event ) { $this->id = $event->getCampaignId(); $this->channels = $event->getRecommendedChannels()->toArray(); $this->campaignPrice = $event->getCampaignPrice(); $this->estimatedOutcome = $event->getEstimatedOutcome(); $this->targetGroup = $event->getTargetGroup(); $this->setInitialRecommendation( $this->channels, $this->estimatedOutcome, $this->campaignPrice ); }

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// Campaign.php public function discardCustomization() { $this->guardCannotModifyOrderedCampaign(); if ($this->isCustomized === false) { return; } $this->apply(new CustomizationDiscarded( $this->id, $this->initialRecommendation['channels'], $this->initialRecommendation['campaignPrice'], $this->initialRecommendation['estimatedOutcome'] )); }

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// Campaign.php protected function applyCustomizationDiscarded( CustomizationDiscarded $event ) { $this->channels = $event->getRecommendedChannels(); $this->campaignPrice = $event->getCampaignPrice(); $this->estimatedOutcome = $event->getEstimatedOutcome(); $this->isCustomized = false; }

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Where are the tests?

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Scenario testing

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Given When Then

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Campaign Created For Target Group Add Channel To Campaign Channel Added To Campaign

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$channelId = new ChannelId('42'); $this->scenario ->given([ new CampaignCreatedForTargetGroup( $this->campaignId, // $args ) ]) ->when(new AddChannelToCampaignCommand( $this->campaignId, $channelId )) ->then([ new ChannelAddedToCampaign( $this->campaignId, $this->stubbedChannel($channelId), new CampaignPrice(Money::EUR(40000), Money::EUR(0)), new EstimatedOutcome(/* snip */) ) ]);

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$channelId = new ChannelId('42'); $this->scenario ->given([ new CampaignCreatedForTargetGroup( $this->campaignId, // $args ) ]) ->when(new AddChannelToCampaignCommand( $this->campaignId, $channelId )) ->then([ new ChannelAddedToCampaign( $this->campaignId, $this->stubbedChannel($channelId), new CampaignPrice(Money::EUR(40000), Money::EUR(0)), new EstimatedOutcome(/* snip */) ) ]);

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$channelId = new ChannelId('42'); $this->scenario ->given([ new CampaignCreatedForTargetGroup( $this->campaignId, // $args ) ]) ->when(new AddChannelToCampaignCommand( $this->campaignId, $channelId )) ->then([ new ChannelAddedToCampaign( $this->campaignId, $this->stubbedChannel($channelId), new CampaignPrice(Money::EUR(40000), Money::EUR(0)), new EstimatedOutcome(/* snip */) ) ]);

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$channelId = new ChannelId('42'); $this->scenario ->given([ new CampaignCreatedForTargetGroup( $this->campaignId, // $args ) ]) ->when(new AddChannelToCampaignCommand( $this->campaignId, $channelId )) ->then([ new ChannelAddedToCampaign( $this->campaignId, $this->stubbedChannel($channelId), new CampaignPrice(Money::EUR(40000), Money::EUR(0)), new EstimatedOutcome(/* snip */) ) ]);

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Alternative scenario test $channelId = new ChannelId('42'); $this->scenario ->given([ new CampaignCreatedForTargetGroup( $this->campaignId, // $args ) ]) ->when(function (Campaign $campaign) { $campaign->addChannel($channelId) }) ->then([ new ChannelAddedToCampaign( $this->campaignId, $this->stubbedChannel($channelId), new CampaignPrice(Money::EUR(40000), Money::EUR(0)), new EstimatedOutcome(/* snip */) ) ]);

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You can do something similar to test your read models

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Using the history to correct mistakes

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Replaying events to fix read models

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Replaying events to create new read models

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Very powerful

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Very tricky

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Replaying events Event Store Read Model Store e v e n t b u s Read Model Store

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Replaying events Event Store Read Model Store e v e n t b u s Email Notification Processor

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Find a solution for your specific problem

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Questions? joind.in/16227 freenode: #qandidate github.com/qandidate-labs/broadway

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Symfony User Group The Renaissance 10 december http://www.meetup.com/Symfony-User-Group-NL