E-Commerce sample of Event Sourcing with EvenStoreDB

Sample is showing the typical flow of the Event Sourcing app with EventStoreDB.

Prerequisities

1. Install git - https://git-scm.com/downloads.
2. Install .NET Core 5.0 - https://dotnet.microsoft.com/download/dotnet/5.0.
3. Install Visual Studio 2019, Rider or VSCode.
4. Install docker - https://docs.docker.com/docker-for-windows/install/.
5. Open ECommerce.sln solution.

Running

1. Go to docker and run: docker-compose up.
2. Wait until all dockers got are downloaded and running.
3. You should automatically get:
   • Postgres DB running
   • PG Admin - IDE for postgres. Available at: http://localhost:5050.
     • Login: [email protected], Password: admin
     • To connect to server Use host: postgres, user: postgres, password: Password12!
   • EventStoreDB UI: http://localhost:2113/
4. Open, build and run ECommerce.sln solution.
   • Swagger should be available at: http://localhost:5000/index.html

Overview

It uses:

• CQRS with MediatR,
• Stores events from Aggregate method results to EventStoreDB,
• Builds read models using Subscription to $all.
• Read models are stored as Marten documents.
• App has Swagger and predefined docker-compose to run and play with samples.

Write Model

• Most of the write model infrastructure was reused from other samples,
• Added new project Core.EventStoreDB for specific EventStoreDB code,
• Added EventStoreDBRepository repository to load and store aggregate state,
• Added separate IProjection interface to handle the same way stream aggregation and materialised projections,
• Thanks to that added dedicated AggregateStream method for stream aggregation
• See sample Aggregate

Read Model

• Read models are rebuilt with eventual consistency using subscribe to all EventStoreDB feature,
• Added hosted service SubscribeToAllBackgroundWorker to handle subscribing to all. It handles checkpointing and simple retries if the connection was dropped.
• Added ISubscriptionCheckpointRepository for handling Subscription checkpointing.
• Added checkpointing to EventStoreDB stream with EventStoreDBSubscriptionCheckpointRepository and dummy in-memory checkpointer InMemorySubscriptionCheckpointRepository,
• Added MartenExternalProjection as a sample how to project with left-fold into external storage. Another (e.g. ElasticSearch, EntityFramework) can be implemented the same way.

Tests

• Added sample of unit testing in Carts.Tests:
  • Aggregate unit tests
  • Command handler unit tests
• Added sample of integration testing in Carts.Api.Tests
  • API integration tests

Other

• Added EventTypeMapper class to allow both convention-based mapping (by the .NET type name) and custom to handle event versioning,
• Added StreamNameMapper class for convention-based id (and optional tenant) mapping based on the stream type and module,
• IoC registration helpers for EventStoreDB configuration,

Trivia

1. Docker useful commands
   • docker-compose up - start dockers
   • docker-compose kill - to stop running dockers.
   • docker-compose down -v - to clean stopped dockers.
   • docker ps - for showing running dockers
   • docker ps -a - to show all dockers (also stopped)

Updated to Marten v4 alpha with revolutionary changes to Event Sourcing projections API.

More details in Pull Request: https://github.com/oskardudycz/EventSourcing.NetCore/pull/38/

See also:

• https://jeremydmiller.com/2021/02/09/event-sourcing-with-marten-v4-aggregated-projections/
• https://jeremydmiller.com/2021/03/02/improvements-to-event-sourcing-in-marten-v4/

• Updated projects to .NET 5 from .NET Core 3.1
• Updated packages to latest versions
• Changed the private class into public to workaround new changes in Marten related to codegen
• Renamed test class Task into Issue to workaround Marten issue https://github.com/JasperFx/marten/issues/1647
• Needed to make Aggregates classes public because of current Marten v4 alpha codegen limitation (https://github.com/JasperFx/marten/pull/1655), and .NET limitations https://github.com/dotnet/runtime/issues/12454.

See more in: https://github.com/oskardudycz/EventSourcing.NetCore/pull/32

Unified multiple Core architecture components into projects that are reused acrosss all samples.

Upgraded to newest versions of packages. Breaking changes after upgrade to MediatR 4. Now only Asynchronous handlers are available. Synchronous were removed, and asynchronous were renamed to "regular" eg. IAsyncCommandHandler to AsyncCommandHandler