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![ELASTICSEARCH
class CompanyRegistered {
public $companyId;
public $name;
public $street;
public $city;
}
function handleCompanyRegistered(CompanyRegistered $event) {
$this->elasticsearch->index([
'index' => 'companies',
'type' => 'company',
'id' => $event->companyId,
'body' => [
'name' => $event->name,
'address' => [
'street' => $event->street,
'city' => $event->city
]
]
]);
}](https://image.slidesharecdn.com/cqrsesinthewild-160914091122/85/CQRS-event-sourcing-in-the-wild-24-320.jpg)
![UPCASTING
class UserRegistered_V1 {
public $userId;
public $name;
public $timestamp;
}
class UserRegistered_V2 {
public $userId;
public $name;
public $date;
}
function upcast($event): array {
if (!$event instanceof UserRegistered_V1) {
return [];
}
return [
new UserRegistered_V2($event->userId, $event->name,
$event->timestamp->format("Y-m-d"))
];
}](https://image.slidesharecdn.com/cqrsesinthewild-160914091122/85/CQRS-event-sourcing-in-the-wild-38-320.jpg)
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CQRS & event sourcing in the wild
- 1. CQRS & EVENTSOURCING IN THE WILD MICHIEL ROOK
- 2. ➤ Java, PHP& Scala developer ➤ Consultant, trainer, speaker ➤ Dutch Web Alliance ➤ make.io ➤ Maintainer of Phing ➤ @michieltcs
- 3.
- 4. RAISE YOUR HAND IFYOU HAVE
- 5. heard about CQRS/ Event Sourcing RAISE YOUR HAND IF YOU HAVE
- 6. heard about CQRS/ Event Sourcing followed a tutorial, built a hobby project RAISE YOUR HAND IF YOU HAVE
- 7. heard about CQRS/ Event Sourcing followed a tutorial, built a hobby project used it in production RAISE YOUR HAND IF YOU HAVE
- 8. TOPICS ➤ Quick recap ➤Replays and rebuilds ➤ Event versioning ➤ Concurrency ➤ Scale
- 9.
- 10. ' Event Sourcing ensuresthat all changes to application state are stored as a sequence of events. -Martin Fowler
- 11. ACTIVE RECORD VS.EVENT SOURCING Account number Balance 12345678 €€ 50,00 ... ... Money Withdrawn Account number 12345678 Amount €€ 50,00 Money Deposited Account number 12345678 Amount €€ 100,00 Account Created Account number 12345678
- 12. COMMANDS TO EVENTS DepositMoney Account number 12345678 Amount €€ 100,00 Money Deposited Account number 12345678 Amount €€ 100,00 class DepositMoney { public $accountNumber; public $amount; } class MoneyDeposited { public $accountNumber; public $amount; public $timestamp; } function depositMoney(DepositMoney $command) { $this->apply(new MoneyDeposited($command->accountNumber, $command->amount, date())); }
- 13. AGGREGATES class BankAccount { public$accountNumber; public $balance; // command handlers... public function applyAccountCreated(AccountCreated $event) { $this->accountNumber = $event->accountNumber; $this->balance = 0; } public function applyMoneyDeposited(MoneyDeposited $event) { $this->balance += $event->amount; } public function applyMoneyWithdrawn(MoneyWithdrawn $event) { $this->balance -= $event->amount; } }
- 14. AGGREGATE STATE Account number Balance 12345678 €€ 0,00 MoneyWithdrawn Account number 12345678 Amount €€ 50,00 Money Deposited Account number 12345678 Amount €€ 100,00 Account Created Account number 56789012 Account number Balance 12345678 €€ 100,00 Account number Balance 12345678 €€ 50,00
- 15. CQRS ➤ Command QueryResponsibility Segregation ➤ Separate writes (events) and reads (UI) ➤ Optimize for reads!
- 16. Domain Event Bus Event Handlers Command Repository DataLayer Database Database Event Store commands events events queries DTOs Aggregates
- 17. PROS AND CONS ➤Domain fit ➤ Testing ➤ Audit trail ➤ Scalability ➤ Complexity ➤ Library support / maturity
- 18.
- 19.
- 20. PROJECTIONS AND READMODELS User Registered User Registered User Unregistered Number of active users?
- 21. PROJECTIONS AND READMODELS User Registered User Deactivated User Reactivated Number of active users? User Registered User Unregistered
- 22. PROJECTIONS AND READMODELS User Registered Event Handler Number of active users +1 User Unregistered Event Handler Number of active users -1
- 23. PROJECTIONS AND READMODELS Events Event Handler(s) Storage
- 24. ELASTICSEARCH class CompanyRegistered { public$companyId; public $name; public $street; public $city; } function handleCompanyRegistered(CompanyRegistered $event) { $this->elasticsearch->index([ 'index' => 'companies', 'type' => 'company', 'id' => $event->companyId, 'body' => [ 'name' => $event->name, 'address' => [ 'street' => $event->street, 'city' => $event->city ] ] ]); }
- 25. READ MODEL UPDATES ➤New type ➤ New structure ➤ Based on existing events ➤ Generate from scratch?
- 26. REBUILDING Stop application Remove old read model Loop over events Applyto read model Start application
- 27. ZERO DOWNTIME Loop over existing events Applyto new read model Apply queued events Start using new read model New events Queue
- 28. ELASTICSEARCH: MAPPING CHANGE Create indexwith new mapping Reindex existing documents Apply queued events Start using new index New events Queue
- 29. CHALLENGE: LONG RUNNINGREBUILDS ➤ Alternatives ➤ Distributed ➤ In memory ➤ Partial ➤ Background
- 30. CHALLENGE: SIDE EFFECTS UserRegistered User Id 123abc Email Address test@example.net Event Handler Exclude during replays!
- 31. CHALLENGE: TRANSACTIONS Event Handler EventHandler Event Event Handler Event Handler ?
- 32. CHALLENGE: EVENTUAL CONSISTENCY ➤Asynchronous event handlers ➤ Reads eventually return the same value ➤ Compare with ACID
- 33.
- 34. DILEMMA ➤ New businessrequirements ➤ Refactoring ➤ New view on events
- 35. NEW EVENTS /VERSIONS ➤ No longer relevant ➤ Renamed ➤ Additional or renamed field(s) ➤ Too coarse, too fine
- 36. SUPPORT YOUR LEGACY? ➤Events are immutable ➤ Correct (incorrect) old events with new events
- 37.
- 38. UPCASTING class UserRegistered_V1 { public$userId; public $name; public $timestamp; } class UserRegistered_V2 { public $userId; public $name; public $date; } function upcast($event): array { if (!$event instanceof UserRegistered_V1) { return []; } return [ new UserRegistered_V2($event->userId, $event->name, $event->timestamp->format("Y-m-d")) ]; }
- 39. REWRITING HISTORY Load (subsetof) events Deserialize Modify Serialize Save/replace
- 40. THINGS TO BEAWARE OF Upcasting ➤ Performance ➤ Complexity ➤ Existing projections not automatically updated Rewriting events ➤ Running code that depends on old structure ➤ Breaking serialization ➤ Changing wrong events
- 41.
- 42. CONCURRENT COMMANDS Withdraw Money Accountnumber 12345678 Amount €€ 50,00 Deposit Money Account number 12345678 Amount €€ 100,00 ?
- 43. PESSIMISTIC LOCKING Withdraw Money Accountnumber 12345678 Amount €€ 50,00 Deposit Money Account number 12345678 Amount €€ 100,00 Account number Balance 12345678 €€ 100,00 Account number Balance 12345678 €€ 50,00 wait for lock lock
- 44. OPTIMISTIC LOCKING Withdraw Money Accountnumber 12345678 Amount €€ 50,00 version 1 Deposit Money Account number 12345678 Amount €€ 100,00 version 1 Account number Balance 12345678 €€ 100,00 version 2 ConcurrencyException
- 45.
- 46. PERFORMANCE ➤ Server ➤ Database ➤Framework ➤ Language
- 47. STORAGE ➤ #events ➤ #aggregates ➤#events_per_aggregate ➤ Serializer ➤ Speed ➤ Payload size ➤ Costs
- 48. SNAPSHOTS Events 1 Account Created 2Money Deposited 3 Money Withdrawn 4 Money Deposited SNAPSHOT 5 Money Withdrawn Events 1 Account Created 2 Money Deposited 3 Money Withdrawn 4 Money Deposited 5 Money Withdrawn
- 49. SHARDING ➤ Aggregate Id,Type, Event Timestamp, ... ➤ Rebalancing ➤ Distribution
- 50. ARCHIVING EVENTS ➤ Reduceworking set ➤ Inactive / deleted aggregates ➤ Historic / irrelevant events ➤ Cheaper storage
- 51. FRAMEWORK COMPARISON Framework UpcastingSnapshots Replaying Broadway (PHP) No (PR) No (PR) Not in core Prooph (PHP) MessageFactory Yes, triggers on event count Example code, off line Axon (Java/Scala) Upcaster / UpcasterChain Yes, triggers on event count Yes, ReplayingCluster Akka Persistence (Java/Scala) Event Adapter Yes, decided by actor Yes
- 52. BROADWAY VS PROOPH classTodoItem extends EventSourcedAggregateRoot { private $itemId; public function __construct(PostTodo $command) { $this->apply(new TodoPosted($command->getItemId())); } public function getAggregateRootId() { return $this->itemId; } public function applyTodoPosted(TodoPosted $event) { echo "Posted: " . $event->getItemId() . "n"; } }
- 53. BROADWAY VS PROOPH classTodoItem extends AggregateRoot { private $itemId; public function __construct(PostTodo $command) { $this->recordThat(new TodoPosted($command->getItemId())); } protected function aggregateId() { return $this->itemId; } public function whenTodoPosted(TodoPosted $event) { echo "Posted: " . $event->getItemId() . "n"; } }
- 54.