Since the requirement of the Wallet App is keeping track of all the users, wallets it contains, wallet transaction history and also the solution is provided as reusable library code.
So to be practical and useful, I specified the scope of making a small library to implement a mimial event sourcing framework, which is easy to apply event sourcing pattern to exsiting ActiveRecord models.
To demonstrate how to use this lib, there is an example of using ruby on rails, which is the Wallet App.
This lib provieds three core files.
/models/events/base_event.rb
/models/dispatcher.rb
/models/commands/base.rb
Events::BaseEvent is the abstract class. Each model (or Aggregate) has its own event table to records all the changes to this Aggregate.
Events::Dispatcher can be used to publish event, you can subscribe to an event and there is a Reactor to react to this event. For example, send money to another wallet, the receiver will react to a Pay event and then receive the money.
Command Base is a mixin, you can include it to a command class, this command is similar to ViewModal in MVVC architecture. it provides validations and creating event.
This app is built on Postgress as the database.
- bundle install
- yarn install
- bundle exec db:create
- bundle exec db:migrate
- bundle exec rails s
Then you can view the app in localhost:3000
The interface is mainly made in users_controller.rb and wallets_controller.rb and the business logic is organised in models/commands and models/events/
Normally Event Sourcing pattern comes with CQRS, this lib make changes to aggregate when the event is created Synchronously.
This app can try to make some changes to use CQRS.