Understanding Responsibility Segregation in Elixir with Commanded Library

This detailed article presents the Command Query Responsibility Segregation (CQRS) and Event Sourcing patterns within the Elixir ecosystem, utilizing the Commanded library to facilitate these concepts. CQRS refers to the separation of command (state-changing actions) and query (data retrieval actions) responsibilities, allowing for different persistence strategies. Event Sourcing, on the other hand, involves storing data as a series of events, preserving context and supporting features like audit logs and time travel. The author demonstrates how to apply these patterns in practice with the Commanded library, including setting up an event store, defining commands and events, using aggregates, dispatchers, handlers, projectors, and projections. The article also explores the implications of eventual consistency in an Elixir application and provides a practical guide through illustrative examples and code snippets.