Event Sourcing in practice @ Qandidate.com

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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{
$campaignId,
$this->companyId,
$this->accountId,
)
));
);
}

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{
$campaignId,
$this->companyId,
$this->accountId,
)
));
);
}

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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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) {
$this->recommender
);
}

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) {
$this->recommender
);
}

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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
$campaignId,
$companyId,
$accountId,
$targetGroup,
));
return $campaign;
}

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Action → Reaction
// Campaign.php
$campaignId,
$companyId,
$accountId,
$targetGroup,
));
return $campaign;
}

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Action → Reaction
// Campaign.php
$campaignId,
$companyId,
$accountId,
$targetGroup,
));
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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{
$this->playhead++;
$this->playhead,
new Metadata(),
$event
);
}

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Campaign
Event Store
Create Campaign
For Target Group
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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{
$this->playhead++;
$this->playhead,
new Metadata(),
$event
);
}

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{
$this->playhead++;
$this->playhead,
new Metadata(),
$event
);
}

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{
$this->playhead++;
$this->playhead,
new Metadata(),
$event
);
}

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) {
$this->recommender,
$this->portfolio,
$this->aidaMetricsCalculator
);
}

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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
{
$eventStream
);
}

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Saving the events
{
$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
Target Group

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How would we load a
campaign?

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Campaign
Event Store
Target Group

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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);
}
}
public function initializeState(DomainEventStreamInterface $stream)
{
foreach ($stream as $message) {
$this->playhead++;
$this->handleRecursively($message->getPayload());
}
}

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{
try {
);
}
}
{
$this->playhead++;
}
}

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{
try {
);
}
}
{
$this->playhead++;
}
}

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{
try {
);
}
}
{
$this->playhead++;
}
}

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

) {
);
}

) {
);
}

) {
);
}

// 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
) {
$this->id,
$channelInCampaign,
$campaignPrice,
$estimatedOutcome
));
}

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// Campaign.php
) {
$this->id,
$channelInCampaign,
$campaignPrice,
$estimatedOutcome
));
}

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// Campaign.php
protected function applyChannelAddedToCampaign(
ChannelAddedToCampaign $event
) {
$this->channels[] = $event->getChannel();
$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
Target Group

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Campaign
Event Store
Target Group
Read Model
Store

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

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Saving the events
{
$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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) {
));
}

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) {
));
}

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// CampaignDetailsProjector.php
) {
$campaignDetails = new CampaignDetails(
$event->getRecruiterId(),
$event->getTargetGroup(),
$event->getRecommendedChannels()->toArray()
);
$campaignDetails->updatePrice($event->getCampaignPrice());
$campaignDetails->updateEstimatedOutcome(
$event->getEstimatedOutcome()
);
$this->repository->save($campaignDetails);
}

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) {
);
);
}

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) {
);
);
}

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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(
) {
$this->id = $event->getCampaignId();
$this->channels = $event->getRecommendedChannels()->toArray();
$this->targetGroup = $event->getTargetGroup();
$this->setInitialRecommendation(
$this->channels,
$this->estimatedOutcome,
$this->campaignPrice
);
}

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// Campaign.php
public function discardCustomization()
{
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->isCustomized = false;
}

Where are the tests?

Scenario testing

Given
When
Then

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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$this->scenario
->given([
$this->campaignId,
// $args
)
])
$this->campaignId,
$channelId
))
->then([
$this->campaignId,
)
]);

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$this->scenario
->given([
$this->campaignId,
// $args
)
])
$this->campaignId,
$channelId
))
->then([
$this->campaignId,
)
]);

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$this->scenario
->given([
$this->campaignId,
// $args
)
])
$this->campaignId,
$channelId
))
->then([
$this->campaignId,
)
]);

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Alternative scenario test
$this->scenario
->given([
$this->campaignId,
// $args
)
])
->when(function (Campaign $campaign) {
$campaign->addChannel($channelId)
})
->then([
$this->campaignId,
)
]);