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DDD, CQRS & ES lessons learned (Gitte Vermeiren)
The document discusses the challenges and lessons learned when implementing Event Sourcing (ES), Command Query Responsibility Segregation (CQRS), and Domain-Driven Design (DDD). It outlines several problems encountered, such as the need for unique identifiers for documents, difficulties in debugging, and data management issues. The document also highlights potential solutions and resources for overcoming these challenges.
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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 notsimply Use ES, CQRS & DDD
- 3. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository EventStore Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events
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- 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 EventStore 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 EventStore Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Use a domain service
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- 16. DomainEvent Id AggregateId Version Raised repo.GetById<Aggregate>(aggregateId); Get/Store events basedon type, not on eventproviderId?
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- 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 Readthe entire event stream Save the entire event stream
- 20. UI Commands Command Bus Command Command Handler Domain Model Domain Model Domain Model Repository EventStore Aggregates Events Event Handler Data Thin Data Layer Query DTO Event Bus Events Replay needed
- 22. Event Versioning withan EventUpdater
- 23. AnAggregate _somePrivateStuff = 0 onSomeEvent: _somePriveStuff= somevalue; SomeEvent AnotherEvent AndAnotherEvent Replay Repository.GetById<AnAggregate>(aggregateId);
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- 28. AnAggregateSnapshot Repository.GetById<AnAggregate>(aggregateId); _version = 666 SomeEvent Version= 667 AnotherEvent Version = 668 AndAnotherEvent Version = 669 AnAggregate _somePrivateStuff = 0 onSomeEvent: _somePriveStuff = somevalue; Replay
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- 31. Hard to usein debugging Hard to do data updates Hard to query
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- 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 EventStore 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
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- 38. And for thegood news?
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