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Event Sourcing & CQRS using the Critter Stack
- 1. CQRS and Event Sourcing with the “CritterStack” August 14th, 2024
- 2. Goals of this Workshop •Introduction to Event Sourcing • What goes into building a robust Event Driven Architecture • Convincing you all to use the “Critter Stack!” • Make you love the idea of low ceremony code
- 3. Environmental Requirements • Install .NET8 SDK • Install Docker Desktop • Clone https://github.com/Jjasperfx/EventDrivenArchitectureWorkshop • From the command line, run “docker compose up –d”
- 4. Building a CritterStack Application Series
- 5. About Me • Ownerand Founder of JasperFx Software LLC • Marten Core Team & Wolverine Project Leader • Longtime OSS Author (StructureMap et al) • https://jeremydmiller.com
- 6. The “Critter Stack” • Marten,Wolverine, Weasel (“Mustelidae”) • Toolset for Event Driven Architecture • Low ceremony coding model • High testability & low friction integration testing • Low friction developer experience • Robust system development
- 7. Weasel • OSS Libraryfor Low Level Database Utilities • Supporting Actor • Command Batching • SQL Generation • Schema Migrations • Makes ADO.Net less aggravating
- 8. Marten • Open Source.NET Library • Uses PostgreSQL for Persistence • ACID Compliant Document Store • Integrated Event Sourcing
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- 10. Why a Document Database? •Because you can develop faster, full stop • Handles deep nested structures • Great story for polymorphic entities • Advantageous when entities are self-contained
- 11. Event Sourcing A styleof persistence where the single source of truth, system state is a read only, append only sequence of all the events that resulted in a change in the system state.
- 12. Advantages to Event Sourcing •Usage of Business Language • Audit Log • Temporal Querying / “Time Travel” • Retrofitting Metrics • Complement to CQRS • Concurrency
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- 14. Event Storming –Help Desk Service
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- 16. Marten Terminology • Event -a persisted business event representing a change in state or record of an action taken in the system • Stream - a related "stream" of events representing a single business workflow or concept • Projection - any strategy for generating a “read side” view of the system state from the events • Aggregate – in Marten terms, a flavor of projection that combines a related set of events into a single view
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- 18. Our first ”Incident”Projection
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- 20. Projection Considerations • Inline –simple approach, strong consistency, slower ”writes”, faster “reads” • Live – simple approach, strong consistency, faster “writes”, slower “reads” • Async – more complicated, eventual consistency, fast “writes”, fast “reads”
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- 23. CQRS •Command Query Responsibility Segregation •Asoftware architectural pattern where “reads” and “writes” are strictly segregated within the system
- 24. Building Command Handlers • Validatecommand inputs • Fetch existing “write” model state • Determine what new events to append • Managing transactions • Concurrency • Error handling and resiliency • Publishing events • Observability
- 25. Automated Integration Testing •Knowninputs, expected outcomes •Marten has built in test helpers for controlling system state in tests •“Self-Contained Tests”
- 26. Guest starring… Alba Easy Integrationtesting for ASP.NET Core https://jasperfx.github.io/alba/ Oakton Parsing and Utilities for Command Line Tools in .Net https://jasperfx.github.io/oakton
- 27. Building a TestHarness
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- 29. Wolverine • Open Source.NET Framework • Command Executor • Local Queueing • Asynchronous Messaging • Alternative HTTP Service Framework • Strong Integration with Marten
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- 33. Drink the Koolaid anduse Wolverine for HTTP
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- 38. Integration Testing for WolverineMessage Handling
- 39. Vertical Slice Architecturethe Wolverine Way
- 40. Asynchronous Messaging with Wolverineand Rabbit MQ
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- 42. Error Handling andResiliency
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- 49. Open Telemetry andMetrics
- 50. Multi- Tenancy • Marten Storage •Conjoined Multi Tenancy • Separate Database per Tenant • Wolverine Tenant Id Propagation • Wolverine Tenant Id Detection
- 51. Resources • JasperFx Software– https://jasperfx.net • Marten – https://martendb.io • Wolverine – https://wolverine.netlify.app