CQRS with Event Source in Functional sauce served by Kotlin
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The document discusses using CQRS with event sourcing and functional programming principles to build the backend for a pizza ordering chatbot. It covers key concepts like commands, queries, events, entities, aggregates and actors. Commands emit events to change state, events are processed by queries to maintain consistency, and events are folded into entities. The overall architecture uses Kotlin features and functional programming patterns like immutability to implement the command and query handling logic.
CQRS with Event Source in Functional sauce served by Kotlin
- 1. @Ramtop CQRS with Event Source in Functional sauce served by Kotlin Uberto Barbinigithub.com/uberto/anticapizzeria
- 2. @Ramtop CQRS + Event Source Very powerful but a bit intimidating… Can we do better?
- 3. @Ramtop Functional Programming ● Immutability ● Purity ● Higher order functions ● Transformations and preserving properties
- 4. @Ramtop Functional vs OO Programming
- 5. @Ramtop Command ● A Command is a request for changing the internal state of the system ● A Command can “fail” if is not congruent with the current state of the System ● Each Command is executed in an atomic context
- 6. @Ramtop Query ● A query ask for a snapshot of the state ● Queries typically need different data and denormalization from domain model. So we separate the models in CQRS. ● Queries are eventually consistent with the domain
- 7. @Ramtop Values-Entities ● They represent the state of the domain ● In functional programming everything is immutable, so there is no identity ● To keep state changes we have Algebraic Data Types
- 8. @Ramtop Aggregates ● An aggregate has all the information for a transaction unit ● Aggregates is what Events fold to ● They are composed by Entities
- 9. @Ramtop Event ● Events are the “atoms” of System state change ● Nothing can change without an event, every event can change only one entity ● Entity + Event => Entity
- 10. @Ramtop Actors ● More powerful and easy to use concurrency model than Threads/Locks ● They communicate asynchronously and potentially remotely ● Useful for Bounded Contexts and Services
- 11. @Ramtop
- 12. @Ramtop Antica Pizzeria ● Real application is about finance products booking but a pizzeria has a surprising similar domain ● We want to do implement the backend for a ChatBot that will assist booking and enquires about orders.
- 13. @Ramtop Kotlin Syntax ● No semicolon! ● String? Is a different type from String ● myFun{println(it)} is equivalent to myFun(x -> println(x)) ● val xy is declaring xy immutable var xy is declaring xy mutable ● User(“Joe”) is equivalent to Java new User(“Joe”)
- 14. @Ramtop Commands
- 15. @Ramtop Commands
- 16. @Ramtop Queries
- 17. @Ramtop Actors (where we can put all this stuff)
- 18. @Ramtop Commands emit Events (it’s the only way to change)
- 19. @Ramtop Events
- 20. @Ramtop Queries listen to Events (to keep up with the changes)
- 21. @Ramtop Let's fold Events (to create Entities)
- 26. @Ramtop We can now process C&Q (Fun with Kotlin ExtFun)
- 29. @Ramtop
- 30. @Ramtop