Added EventStoreDB E-Commerce initial samples

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: admin@pgadmin.org, 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)