As a follow-up to our interview with Jimmy Nillson, we bring you a review of Applying Domain-Driven Design and Patterns and a sample chapter from courtesy of Addison Wesley Professional.
What makes this book particularly refreshing is the level of honesty in conveys. Unlike some books of this sort that focus on the merits of the chosen techniques and flaws of the others, this book gives a fair treatment to everything it touches on. There is a heavy emphasis on the flaws of each technique discussed, even those of Domain-Driver Design, and ways to minimize their impact.
In the sample chapter, Preparing for Infrastructure, Nillson discusses some topics such as persistence ignorant (PI) classes and querying.
So let's assume we want to use PI. What's it all about? Well, PI means clean, ordinary classes where you focus on the business problem at hand without adding stuff for infrastructure-related reasons. OK, that didn't say all that much. It's easier if we take a look at what PI is not. First, a simple litmus test is to see if you have a reference to any external infrastructure-related DLLs in your Domain Model. For example, if you use NHibernate as your O/R Mapper and have a reference to nhibernate.dll, it's a good sign that you have added code to your Domain Model that isn't really core, but more of a distraction.