fmodel-ktor-demo (EventSourcing)

A demo/example project for the imaginary restaurant and order management. It is backing the Fmodel Reference Guide.

It demonstrates how to run our unique domain and orchestrate it in an EventSourced/EventDriven way.

this blueprint is an outcome of the event-modeling process

Fmodel

This project is using Fmodel - Kotlin, multiplatform library.

Fmodel is:

• enabling functional, algebraic and reactive domain modeling with Kotlin programming language.
• inspired by DDD, EventSourcing and Functional programming communities, yet implements these ideas and concepts in idiomatic Kotlin, which in turn makes our code
  • less error-prone,
  • easier to understand,
  • easier to test,
  • type-safe and
  • thread-safe.
• enabling illustrating requirements using examples
  • the requirements are presented as scenarios.
  • a scenario is an example of the system’s behavior from the users’ perspective,
  • and they are specified using the Given-When-Then structure to create a testable/runnable specification
    • Given < some precondition(s) / events >
    • When < an action/trigger occurs / commands>
    • Then < some post condition / events >

Check the tests!

with(orderDecider) {
    givenEvents(listOf(orderCreatedEvent)) {         // PRE CONDITIONS
        whenCommand(createOrderCommand)              // ACTION
    } thenEvents listOf(orderRejectedEvent)          // POST CONDITIONS
}

Fstore-SQL

This project is using PostgreSQL powered event store, optimized for event sourcing and event streaming.

Fstore-SQL is enabling event-sourcing and pool-based event-streaming patterns by using SQL (PostgreSQL) only.

• event-sourcing data pattern (by using PostgreSQL database) to durably store events
  • Append events to the ordered, append-only log, using entity id/decider id as a key
  • Load all the events for a single entity/decider, in an ordered sequence, using the entity id/decider id as a key
  • Support optimistic locking/concurrency
• event-streaming to concurrently coordinate read over a streams of events from multiple consumer instances
  • Support real-time concurrent consumers to project events into view/query models

Tools

• EventModeling - a method of describing systems using an example of how information has changed within them over time.

Patterns

• EventSourcing
• CQRS

Prerequisites

• Java 17
• Docker

Technology

• Fmodel - Domain modeling with Kotlin
• Ktor (HTTP)
• Kotlin (Coroutines, Serialization)
• Arrow (Fx Coroutines, ...)
• Postgres (event store, projections)

Run & Test

This project is using Gradle as a build and automation tool.

Test:

./gradlew check

Run:

Make sure you have Postgres installed and running.

Alternatively, you can use Docker to run PostgreSQL.

docker run --name postgres -e POSTGRES_PASSWORD=postgres -p 5432:5432 -d postgres

Check the connection URL in application environment variables

./gradlew run

Run in Docker

Make sure you have Docker installed and running.

Build OCI (docker) image:

./gradlew publishImageToLocalRegistry

Run application and Postgres database:

docker-compose up

Further Reading

• Check the FModel reference guide
• Read the blog
• Learn by example on the playground
• Spring Boot version of this project.

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