Where do I find some good examples for DDD?
I'm learning about Domain Driven Design, however there are some practical issues that are confusing to me that I think seeing some good samples might clear up.
Does anyone know of some good working code samples that do a good job of modelling basic DDD concepts?
Particularly interested in
- An illustrative Domain Model
- Repositories
- Use of Domain/Application Services
- Value Objects
- Aggregate Roots
Answer
The difficulty with DDD samples is that they're often very domain specific and the technical implementation of the resulting system doesn't always show the design decisions and transitions that were made in modelling the domain, which is really at the core of DDD. DDD is much more about the process than it is the code. (as some say, the best DDD sample is the book itself!)
That said, a well commented sample app should at least reveal some of these decisions and give you some direction in terms of matching up your domain model with the technical patterns used to implement it.
You haven't specified which language you're using, but I'll give you a few in a few different languages:
DDDSample - a Java sample that reflects the examples Eric Evans talks about in his book. This is well commented and shows a number of different methods of solving various problems with separate bounded contexts (ie, the presentation layer). It's being actively worked on, so check it regularly for updates.
dddps - Tim McCarthy's sample C# app for his book, .NET Domain-Driven Design with C#
S#arp Architecture - a pragmatic C# example, not as "pure" a DDD approach perhaps due to its lack of a real domain problem, but still a nice clean approach.
With all of these sample apps, it's probably best to check out the latest trunk versions from SVN/whatever to really get an idea of the thinking and technology patterns as they should be updated regularly.