Game Rental Application

Description

The "Game Rental" application showcases how Axon Framework and Axon Server or AxonIQ Cloud can be used during software development. The domain focused on is that of rental services from the perspective of a video game store.

This repository provides just such an application, albeit a demo rather than a full-fledged solution. It serves the personal purpose of having a stepping stone application to live code during presentations. I intend to build upon this sample during consecutive talks, further enhancing its capabilities as time progresses.

For others, I hope this provides a quick and straightforward look into what it means to build an Axon-based application.

Due to its nature of being based on Axon, it incorporates DDD, CQRS, Event Sourcing, and an overall message-driven solution to communicate between distinct components.

Demo Recordings with different Game Rental implementations

Since I aim to use this project for some time, it'll change through its lifecycle. Most notably, I'll keep it up to date with recent versions of the dependencies.

Due to this, recordings from previous iterations of this project will likely show slight deviations. However, the taken steps during those recordings will remain intact.

Project Traversal

Distinct branches will be (made) available per public speaking, sharing a start and final solution branch separately. Additionally, several branches representing the steps throughout the lifecycle of the "Game Rental" application will be present, allowing you to:

• Check out the exact step that interest you.
• Perform a git reset --hard step# to reset your current branch.

Next to providing the convenience of showing the flow, it also serves as a backup during the presentation.

This project currently contains the following steps:

1. The core-api, containing the commands, events, queries, and query responses.
2. The command model has been created, showing a Game aggregate.
3. The application connects to AxonIQ Console and AxonIQ Cloud through the added AxonIQ Console and Axon Server properties in the application.properties.
4. The query model, a GameView, is provided, created/updated, and made queryable through the GameCatalogProjector.
5. This step includes the Reactor Extension, which is used by the GameRentalController.
6. This step introduces cleaner distributed exceptional handling. It does so by throwing specifics exceptions in @ExceptionHandler annotated functions in the Game aggregate and GameCatalogProjector, containing an ExceptionStatusCode.
7. Spring's @Profile{{profile-name}) annotation has been added to the Game, GameCatalogProjector, GameViewRepository and GameRentalController, allowing for application distribution.
8. Preparation to introduce another endpoint based on RSocket, by renaming the controller to contain "rest" in the name and by extracting the exception mapping registration.
9. Introduce the GameRentalRSocketController, providing an entry point to the application using RSocket.
10. Add the "reservations" query end, invoking a ReservationService once a game is returned. Since this service only has a flunky implementation, attach a dead-letter queue to the reservations processing group to deal with errors.

Running and testing the application

As this is a Spring Boot application, simply running the GameRentalApplication is sufficient. However, Spring profiles are present, which allow for running portions of this application. More specifically, there's a command, query, ui, rsocket, and reservations profile present, thus separating the Game aggregate, GameCatalogProjector, GameRentalRestController, GameRentalRSocketController, and reservation specifics components into distinct groups. Furthermore, when you use IntelliJ, you can use the "Run Configurations" from the ./.run to speed up the startup process.

The application does expect it can make a connection with an Axon Server instance. Ideally, Axon Cloud is used for this, as is shown in step 3. If you desire to run Axon Server locally, you can download it here.

Unit Tests

Any new components introduced in a step include unit tests. These can be used to better understand the project.

For validating the application's internals, you can run the tests, use the REST endpoint, or connect with the RSocket endpoint.

When testing through the REST endpoint, IntelliJ Ultimate you can use the included .http files (in the http-requests folder of this project). The 1-register-games.http allows for the registration of several games to build a base catalog. The 2-rent-return-find.http file contains rent, return, and find operations for testing. The 3-bulk-rent-return.http file contains a bulk of rent and return operations for a single game to test bulk. The 4-dead-letter-management.http file contains the endpoint to process dead-letters.

When testing through RSocket, the most straightforward approach is to install the RSocket Client CLI, or rsc for short. The README of rsc provides concrete explanations on how to install it in your environment.

With rsc in place, you can use the following commands to test the application:

• Register a game - rsc --debug --request --route register --data="{\"gameIdentifier\":\"8668\",\"title\":\"Hades\",\"releaseDate\":\"2020-09-17T00:00:01.000009Z\",\"description\":\"Roguelike dungeon crawler set in ancient Greek mythology\",\"singleplayer\":true,\"multiplayer\":false}" tcp://localhost:7000
• Rent a game - rsc --debug --fnf --route rent --data="{\"gameIdentifier\":\"8668\",\"renter\":\"Ben Wilcock\"}" tcp://localhost:7000
• Return a game - rsc --debug --fnf --route return --data="{\"gameIdentifier\":\"8668\",\"renter\":\"Ben Wilcock\"}" tcp://localhost:7000
• Find a game - rsc --debug --request --route find --data="8668" tcp://localhost:7000
• Watch the game catalog - rsc --debug --stream --route catalog tcp://localhost:7000

Starting your own Axon project

The steps this project traverses show a common approach towards constructing an Axon application. If you want to begin from scratch, consider these key aspects:

• Use the AxonIQ Initializr to kick-start your project.
• Use Axon Cloud Console to connect your application to a context. Using Axon Cloud allows you to persist your events and distribute commands, events, and queries.
• If you want a longer learning experience, please take a look at the AxonIQ Academy.
• Whenever anything is unclear, check out the Reference Guide or drop a question on the forum.