Design Patterns on Software Engineering Thoughts

CQRS (and Event-Driven) Anti-Patterns

Fri, 21 Jul 2023 21:22:11 +0100

Over the years I have worked on a number of systems that would be classed as event-driven, and some of these have also implemented various parts of the CQRS pattern. More recently I’ve been working on systems and services that utilise the full gambit of CQRS and Event Sourcing. These have primarily been built using Axon Framework to provide the technical infrastructure.

While these approaches generally lead to really well structured systems, as with all software development, there are always some anti-patterns that tend to emerge. These make the solutions more difficult to understand, maintain and enhance.

The Essence of Axon Framework

Thu, 06 Jul 2023 17:39:58 +0100

Axon Framework provides an underlying technology platform to allow building of solutions that utilise the CQRS and Event Sourcing architectural patterns. It combines these with a message bus approach that allows for distribution, location transparency and service redundancy.

In this post, rather than describe Axon Framework in great detail, I just want to focus on the main essence of this framework. More details can be found in the resources section at the end of the post.

The Essence of Event Sourcing

Thu, 06 Jul 2023 15:29:25 +0100

Event Sourcing is a really interesting pattern in software engineering. It is an alternative approach to maintaining the state of a domain model and managing its persistence.

There’s a wealth of great material around this pattern and how to use it for building software. If you’d like more information then I’ve included a section at the end of this post with a list of useful resources.

In this post, rather than explain all the details of Event Sourcing, I want to just focus on what I think is the essence of this pattern. Armed with this information you can then go off and explore the subject in more detail.

The Essence of CQRS

Wed, 05 Jul 2023 17:07:43 +0100

I think one of the most interesting patterns in software engineering is Command Query Responsibility Segregation (CQRS). It is a super powerful way of thinking about certain problems and a way of building systems that solve these problems.