Last night, I had a Skype/SharedView session with a buddy in Arkansas trying to apply DDD and “best practices” to an application he was building. He wanted to use all the ALT.NET tools he’s heard so much about, such as NHibernate, StructureMap and so on. The problem came when he went to go look at the sample applications for “Floogle Architecture”, and was basically stopped dead in his tracks. His question to me was, “do I really have to do all this? It seems like a little overkill”. He had looked at several reference applications for every different Floogle Architecture out there, and all confused more than enlightened.
Back when I was getting started trying to apply design principles to my work, I also yearned for that golden reference application that would just tell me what I needed to do, or at least show me what I shouldn’t do. I remember looking at JP Boodhoo’s application he built after a Nuthin But Dot Net course, and I had the same thoughts. “Do I really have to do all this? It seems like a little overkill.” What my buddy and I were missing was context.
Earlier that day, I had a Q&A session with another buddy in town that’s been developing Rails apps to production for around 4 years. Over the course of the past couple of years or so, I’ve also built up a set of mental best practices when it comes to building ASP.NET MVC applications. But something had been nagging me. Rails folks have built large, testable, scalable applications with far far less moving parts. Why do I need all these moving parts, indirections, abstractions and so on to be successful, when plenty of other folks are successful without them? Talking with these two folks in one day reminded me (again): Context is king.
The Right Way versus the Better Way
My .NET buddy was building a small application. It had something like 4 entities and less than 10 screens. It was a small application built for a specific purpose, and wasn’t really going to get much bigger. The Floogle Architecture reference applications are built with a much different context . They could be for applications with hundreds of controllers, dozens upon dozens of entities, and very complex screens. However, all of that context is missing in each respective reference application.
One of the sticking points from Eric Evans when describing DDD was that DDD was never meant to be applied to every solution. It’s hard, it’s complex, and it takes a lot of work and collaboration. In fact, I’ve heard quoted that something like 95% of every application built is not complex enough to warrant a DDD solution. So why is every application I build using the most complex DDD architecture? Am I special? Do I live solely in that 5%, or have I just decided to pick one architecture and apply it globally, no matter the context?
When reviewing my Rails buddy’s actual production Rails app, I was struck by how little code there was, and how flat the architecture is. He had Model, Views and Controllers, and that’s it!. All these pieces that I put in place to support complexity, such as a service layer, dependency injection, factories, indirection, facades, the list goes on, were just not needed in his projects. That’s not to say that the Rails app wasn’t complex. It had complex querying, validation, caching and so on, but it just didn’t need a lot of code to do so. Rails apps don’t even have the concept of a project, yet all Floogle Architecture examples highlight the need for proper layer separation through project structure.
Instead of focusing on the “Right Way” to build an application, I should have focused on the “Better Way”. Sometimes the better way to build an application is to pick the absolute simplest architecture imaginable. Sometimes I don’t need DDD. Sometimes I should just use ActiveRecord, because I just don’t have that domain complexity. When I taught a class for ASP.NET MVC recently, I threw out all my default usage patterns, because building from scratch would pretty much guarantee I built the minimum I actually needed for the context at hand.
One of the books that heavily influenced my understanding of DDD was Jimmy Nilsson’s book. In it, he talks about a “new default architecture”. So I developed an architecture, and applied it pretty much without any thought to every. single. project I worked on. It works well because I know it and understand it, I know its limitations and its constraints, and I know where it can bend complexity-wise. Over the years, this default architecture has grown and grown to basically handle every complexity I’ve ever seen. It’s now very flexible…but very difficult to understand. Pick any reference DDD architecture out there, and you’ll see the same thing.
And that’s where my .NET buddy went wrong. He picked what he thought was a default MVC architecture, when instead it was a reference DDD architecture. His first question should have been, “do I need DDD?”. In his case, decidedly not. In in most cases, decidedly not. When talked with my Rails buddy and mentioned the word “Entity”, I was met with a blank stare. When I sketched out the flow of control in our default architecture, all the pieces we had to develop, his (polite) response was “That looks…hard…”. Yes, yes it is hard. It was completely necessary for the context in which we first developed it, but not for every context.
So why do I try and apply that architecture to every context? Because I’m lousy at predicting complexity. However, Rails folks have happily developed large systems to production without all the pieces I decided I needed for every project. Instead of looking for a “Default Architecture”, I should instead be looking for the “Better Architecture Choice for This Context”.
In the upcoming conversations with my .NET buddy, I’m going to have him throw out all the default architectures he’s looked at. They are interesting from a patterns/style perspective, but utterly useless if you don’t understand the context behind the decisions that brought the samples to that point. And for his case, he just doesn’t need them.
Instead, he needs things like “how do I integrate NHibernate?” and “why should I use a DI framework?”. All the rest can be built up as needed, in a YAGNI fashion, when (or if) the application and the business requirements demand the need for DDD and a complex architecture.