Rethinking CQRS: An Interview on OpenCQRS

Summary

Rethinking CQRS: An Interview on OpenCQRS Golo: Frank, you are one of the managing directors at Digital Frontiers and also one of the architects and main developers of OpenCQRS. Over the past months we've seen a lot of interest in the framework, especially now with version 1.0 out. Some of our customers have even been building production systems with the release candidate for quite a while already, which shows how stable and usable it has been early on. Before we dive into details, let's start at the very beginning: can you tell us a bit about how OpenCQRS came to life? What triggered the idea and what gap were you trying to fill? Frank: To be honest, OpenCQRS started out as an experiment or prototype back in 2024. When the two of us first met each other to talk about EventSourcingDB, I immediately recognized that it contained a lot of hidden gems, such as hierarchical event streams. So, imagining a suitable CQRS framework on top of the EventSourcingDB did not feel like building yet another framework. Instead we were eager to expose those gems to Java developers, who might not even know yet, what they lacked so far. A colleague then started out by implementing a first prototype on a train ride to Hamburg. The result, though in a very early draft state, convinced us that we could come up with a very clear design for CQRS applications. We especially focused on getting rid of some of the annoying relics of typical CQRS frameworks as well. Moving Beyond Aggregates Golo: I know that quite early on you decided to move away from the traditional aggregate pattern, which is a pretty bold step since aggregates have been central to Domain-Driven Design (DDD) for years. Instead, you speak about No Aggregate. Can you explain how this idea evolved and why you deliberately stepped away from the classic approach? Frank: Well, this is definitely the number one relic that we abolished: I've never felt very comfortable with the term "aggregate", as the term does not express clearly, w...