An aggregate root is at the heart of your domain. I am going to dissect a simple implementation of an Aggregate Root and reveal how it works in a CQRS and Event Sourced system. Before we dive in, we need to fly through some terms often used in DDD.
If you’ve been developing for any length of time you’ve probably had to create an audit log. Here’s the question though, are any of these logs, a 100% provable audit of all changes in the system? I’m guessing not. With event sourcing, a 100% provable event log just happens to be a handy by product. So […]
Ever tried to hold a writhing slippery eel in your hands? In case you haven’t, its hard. Building a UI for a CQRS system needn’t be that tricky but you do need to contend with some interesting challenges: The commands ‘complete’ far faster than you may expect – compared to a consistent application. The read […]
When starting out with CQRS, designing the ‘events’ is not always obvious or easy. The more experienced you are, the more likely your habits will lead you astray. This post will help you spot the problems early and stay on the right track.
One of the most liberating things about the CQRS ES way, is the simplicity of the read side. However, if you are new to CQRS you may have wondered how it works. How for example, would it work for a classic master details view? You are not alone, in fact, I am writing this post […]
A common issue I see is understanding the flow of commands, events and queries within a typical CQRS ES based system. The following post is designed to clear up what happens at each step. Hopefully this will help you to reason about your code and what each part does.
Imagine if it was possible, when faced with a potential concurrency issue to programmatically check if any previous ‘events’ actually conflict with the current action being requested. With a CQRS Event Sourced application, it is possible to significantly reduce the problems of concurrency and in the remainder of this article I will show you how.
Sometimes the most effective way for a team to reason about an idea, is to build it. Wireframes are great but a prototype is far more persuasive. Beware however, prototypes have an ugly tendency to morph into the real project or become a blackhole of time. Follow these 10 tips and keep your prototype on […]
There are often times when you want to include static services in your code. For example, when accessing the file system or including an external analytics package. When you do, it presents a testability problem. Every time you exercise the code via a test, that static service is also called. This post explains a simple […]