If you’ve ever built any sort of professional application you will have had to validate user input. Whether it is to ensure a valid email address or something more complicated. There are tried and tested ‘rules’ for doing this safely while being nice the user.
Validate on the client side – makes for a better user experience
And validated on the server – never trust user input
But here’s a question..
If you issue commands rather than send in models, where should the validation occur?
The pen is mightier than the sword. Or so they say. However, this smart LiveScribe 3 pen may just be mightier.
Picture a typical meeting…
You’ve got a whiteboard, notepad, your phone and hopefully the right people in the room. You may even have some funky planning poker cards*.
All good so far.
Now if you are into domain driven design, the chance are you’re going to want to get involved in the meeting. Listen closely to the language used and try to deepen your understanding of the domain. Or at least that’s what you’re supposed to be doing! Continue reading →
Making mistakes is part of programming. Spotting them early can save you time. I’ve started to notice a common set of ‘DDD Mistakes’ which many of us seem to make. And yes, I’ve made them all at some point in my career. This is by no means the definitive list – I’m sure there are more. Continue reading →
Where do you put code for sending emails? Sounds simple right? The funny thing is that if you’re adding it to a CQRS system it can be a little tricky.
It all depends on when you send them. Too early and other processes may fail and you end up sending your email half cocked. And don’t forget event replay. Could be a bit embarrassing re-sending all the emails since your app launched. I was a hairs whisker away from doing just that once!
Events are at the heart of a CQRS Event Sourced system. Which is why changing or upgrading them can be problematic. In this post I’m going to cover a few principles to bear in mind, which should help you avoid hitting the rocks. Before I dive into ‘how to upgrade CQRS events’ I’m going to recap the role Events play in the system. Continue reading →
The nice thing about programming is that everything is black and white.
When designing new features, we all go through a process of discovering requirements. If you are a good developer, you will start to ask questions and probe deeper to find the edge cases. Why? Because you know the edge cases can often take up 80% of the development time. But is that where 80% of the value is? Continue reading →
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. Continue reading →