San Francisco, 1852. With the California Gold Rush at its peak, successful gold-seekers wanted to protect all their precious gold nuggets by storing them in a strong safe. At the time, it wasn’t that easy to have access to a safe though. At the very beginning, it were just a few local merchants that owned one. Not much later, bankers swamped the area hoping to get their piece of the pie - bringing the strongest safes money can buy. ...
Me and Tom just finished doing our Event storming workshop at NCrafts Paris. Although we made a few mistakes along the way, feedback on the workshop was great. I hope to put something out about what we learned facilitating later this week. People talked, discovered and eventually learned a new domain in under two hours. The domain? Two minutes before the workshop we found a domain expert prepared to talk about his coupon start-up. ...
I just returned from Croatia, where I got to speak twice at the second edition of The Geek Gathering. Being such a young conference, I had no idea what to expect. Turns out they have a good thing going on; a small, local and very personal approach to conferences. Speakers both local and international, covering topics that serve the community, not their employer. Together with Tom, I preached Alberto’s Event Storming during a four hour long workshop. As always, people were impressed by how quick you can gain an understanding of a new domain using this technique. Slides of this workshop will be online after I make some tweaks, and try it in Paris on Friday. ...
I have been occupied building a modest Point of Sale system over these last few weeks. Looking at implementing the client, there were two constraints; it needed to run on Windows and it should be able to talk to devices such as a ticket printer and a card reader. Although we could use any Windows client framework, we like building things in the browser better for a number of reasons; platform-independence, familiar user experience, JavaScript’s asynchronous programming model and its incredible rich ecosystem. Having to talk to devices ruled out leveraging the browser to deliver our application though - or didn’t it? ...
Since I intended to avoid Windows at home, I got a Macbook Pro starting out at my new job. Overall it has been a great machine for doing development; it’s fast, light enough to carry around, its battery life is outstanding, it has a screen that’s gentle to the eyes, and full screen apps together with powerful mouse gestures allow me to quickly shuffle between things not missing touch or a second monitor. ...
As you might have noticed reading my last two posts, I have been doing a bit of front-end work using knockout.js. Here is something that had me scratching my head for a little while.. In one of our pages we’re subscribing to a specific event. As soon as that event arrives, we need to reinitialize the model that is bound to our container element. Going through snippets earlier, I remembered seeing the cleanNode function being used a few times - which I thought would remove all knockout data and event handlers from an element. I used this function to clean the element the view model was bound to, for then to reapply the bindings to that same element. ...
While I got to use angular.js for a good while last year, I found myself returning to knockout.js for the current application I’m working on. Where angular.js is a heavy, intrusive, opinionated, but also very complete framework, knockout.js is a small and lightweight library giving you not much more than a dynamic model binder. So instead of blindly following the angular-way, I’ll have to introduce my own set of abstractions and plumbing again; I assume that I’ll end up with a lot less. ...
Last week, we added a dashboard to our back office application that shows some actionable data about what’s going on in our system. Although we have infrastructure in place to push changes to the browser, it seemed more reasonable to have the browser fetch fresh data every few minutes. We split the dashboard up in a few functional cohesive widgets. On the server, we built a view-optimized read model for each widget. On the client, we wrote a generic view model that would fetch the raw read models periodically. ...
In the last project I worked on - processing financial batches - we put a lot of effort in avoiding being silently wrong. The practice that contributed most was being religious about avoiding structures to ever be in an invalid state. Preconditions, invariants, value objects and immutability were key. One of the things we had to do with these structures was writing them to disk in a specific banking format; all the accounts with their transactions for a specific day. To verify the outcome of these functions, we had a decent test suite in place. But still, we felt like we had to do more; the person on the team that had been working in this domain for thirthy years had been relentlessy empathizing - nagging - that bugs here would be disastrous, and would have us end up in the newspaper. That’s when we decided to add postconditions, putting the tests closer to the production code. These would make sure we crashed hard, instead of silently producing something that was wrong. ...
Almost four years ago Udi Dahan introduced an elegant technique that allows you to have your domain model dispatch events without injecting a dispatcher into the model - keeping your model focused on the business at hand. This works by having a static DomainEvents class which dispatches raised events. This customer aggregate raises an event when a customer moves to a new address. public class Customer { private readonly string _id; private Address _address; private Name _name; public Customer(string id, Name name, Address address) { Guard.ForNullOrEmpty(id, "id"); Guard.ForNull(name, "name"); Guard.ForNull(address, "address"); _id = id; _name = name; _address = address; } public void Move(Address newAddress) { Guard.ForNull(newAddress, "newAddress"); _address = newAddress; DomainEvents.Raise(new CustomerMoved(_id)); } } By having a dispatcher implementation that records the events instead of dispatching them, we can test whether the aggregate raised the correct domain event. ...