DDD, CQRS & ES lessons learned (Gitte Vermeiren)
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ES, CQRS & DDD: Lessons learned and walls bumped into DDD, CQRS and Event Sourcing are all based on simple principles. Yet, using them on a project brings with it big challenges and new ways of thinking. In this session Gitte will give you the real life story of how DDD, CQRS and ES was used on one of her latest projects and how she bumped into quite some walls while doing it. You will get an overview of the basic buildup of the application and of the points of most friction. Gitte will also try and give some solutions to the problems the project team went through.
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DDD, CQRS & ES lessons learned (Gitte Vermeiren)
- 1. ES, CQRS & DDD: Lessons Learned (and walls bumped into) Gitte Vermeiren | @GitteTitter
- 2. One does not simply Use ES, CQRS & DDD
- 3. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository Event Store Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events
- 7. Problem 1
- 8. “Every ‘dossier’, ‘scan’, ‘decision’, ... Should have a unique incremental number”
- 9. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository Event Store Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Use an autoincrement column? Use a ‘DossierNumberGenerator’
- 10. DossierNumberGenerator _highestNumber = 0 1. GenerateNext 2. DossierNumberGeneratedEvent 3. onDossierNumberGenerated _highestNumber ++;
- 11. DossierNumberGenerator _highestNumber = 0 onDossierNumberGenerated _highestNumber ++; DossierNumberGeneratedEvent DossierNumberGeneratedEvent DossierNumberGeneratedEvent Replay Repository.GetById<DossierNumberGenerator>(id);
- 12. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository Event Store Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Use a domain service
- 13. Problem 2
- 16. DomainEvent Id AggregateId Version Raised repo.GetById<Aggregate>(aggregateId); Get/Store events based on type, not on eventproviderId?
- 19. WIP AnotherNewRefactoredAggregate ANewRefactoredAggregate anAggregate SomeEvent SomeOtherEvent AndSomeMoreEvent Migration Process SomeEvent SomeOtherEvent AndSomeMoreEvent AndAFunkyEvent https://github.com/vermegi/Eventstream.Migratorhttps://github.com/NEventStore/NEventStore.Migrations Event Store Event Store Read the entire event stream Save the entire event stream
- 20. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository Event Store Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Replay needed
- 22. Event Versioning with an EventUpdater
- 23. AnAggregate _somePrivateStuff = 0 onSomeEvent: _somePriveStuff = somevalue; SomeEvent AnotherEvent AndAnotherEvent Replay Repository.GetById<AnAggregate>(aggregateId);
- 25. Problem 3
- 28. AnAggregateSnapshot Repository.GetById<AnAggregate>(aggregateId); _version = 666 SomeEvent Version = 667 AnotherEvent Version = 668 AndAnotherEvent Version = 669 AnAggregate _somePrivateStuff = 0 onSomeEvent: _somePriveStuff = somevalue; Replay
- 30. Problem 4
- 31. Hard to use in debugging Hard to do data updates Hard to query
- 32. Problem 5
- 34. AnAggregate _somePrivateValue = 0 DoSomething onSomethingHappened _somePrivateValue = something; DoSomething SomethingHappenedEvent
- 35. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository Event Store Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Hard to do data updates Reuse the same logic Do it functional
- 36. Problem 6
- 38. And for the good news?
- 43. Some final thoughts ...
- 45. VISUG Partners