eventstore VS commanded

Since I already had a Postgres database running, I decided to use EventStore rather than installing and babysitting EventStoreDB. To initialize the database and tables, I ran mix event_store.init and mix event_store.create.

My goal is to use LiveView to update a price chart as trades are executed by the system. A LiveView process is a lot like a GenServer, with a bespoke process for each client, executing handle_* functions as the client does things. The first step to real-time chart updates is to trigger one of these handler functions in my LiveView controller when a trade is executed. I'm using Commanded's own EventStore library to dispatch and store my events, so their documentation is the place to start.

This reminds me of Commanded[0] for elixir which also uses Postgresql by default.

[0]https://github.com/commanded/commanded

So, I lied told a half-truth about aggregates. They are not hydrated in-memory for every command / event. In reality, aggregates are implemented with GenServer each caching their state and being managed under the commanded application's supervision tree (ultimately by a DynamicSupervisor called Commanded.Aggregates.Supervisor, to be specific).

The Commanded hex package is a fabulous CQRS library used by some real companies in production, but it doesn't have a great on-ramp.

The context: I'm building a cryptocurrency exchange application. I don't have the business chops to run an actual exchange, so this is just for fun. The application is built in Elixir, using the Commanded framework for CQRS/ES goodness, and Phoenix LiveView because it's the hot new thing that I wanted to learn.