Throughout the course of this chapter you learned about event sourcing, and how it can be a different approach to persistence versus the more traditional approach of persisting current state. You also learned about Akka Persistence, and how you can use it to implement event sourcing in your Akka-based components. Finally, you also learned about how we can leverage tools such as protobuf to help deal with the reality of a constantly evolving event schema.
We changed the bookstore app quite a bit in this chapter, but we still have some holes to close up. We need to get the query functionality working again, as our switch to event sourcing has broken that capability within the app. That will be the main focus of the next chapter, as we dive into CQRS, and how we can use it to build a separate read/query model for our application.