Under the hood and working with .Net, TDD, Software Design, and Agile Stuff
Harris Boyce wrote a response to my
ADO.NET contagion post:
"Soul Vaccination" for Data Access Layers. I think that Harris is quite right in warning us about overusing Object/Relational mapping. While there are still plenty of scenarios where I would forgo an O/R approach for the classic data access layer, I still think that the "Persistence Ignorant" (POCO/PONO/POO whatever) approach for business classes is the way to go for the sake of testability. I think the decision hinges primarily on the amount of business logic in your application (and secondarily on the comfort level of the developers with OO coding in general). Even if I'm not using an O/R tool, I usually use some type of Inversion of Control to keep the rest of the code loosely-coupled from the data access. Before diving into O/R mapping, you might take a look at these resources. Understanding some of the underlying patterns and mechanisms of O/R mapping might help alleviate some of the pain or help in making design decisions.
- Patterns of Enterprise Application Architecture by Martin Fowler has a couple of good chapters about O/R patterns. The chapter on organizing business logic is a canonical read for deciding whether or not to use a Domain Model approach that would lead to using O/R for persistence.
- Applying UML and Patterns by Craig Larman has a great chapter on creating a small persistence framework. This book is my choice as the best introduction to OO programming around.
- This article from Scott Ambler introduces the basics of O/R
- My article on C# Today from a couple years ago, but it's derivative of the guys above.
About Jeremy D. Miller
Jeremy began his IT career writing "Shadow IT" applications to automate his engineering documentation, then wandered into software development because it looked like more fun. Jeremy previously worked as a systems architect building mission critical supply chain software for a Fortune 100 company and learned agile development practices as a .Net consultant at ThoughtWorks, one of the pioneers of agile development. Jeremy is the author of the open source StructureMap (http://structuremap.sourceforge.net) tool for Dependency Injection with .Net and the forthcoming StoryTeller (http://storyteller.tigris.org) tool for supercharged FIT testing in .Net. Jeremy's thoughts on just about everything software related can be found on his weblog "The Shade Tree Developer" at http://codebetter.com/blogs/jeremy.miller, part of the popular CodeBetter site. Jeremy is a Microsoft MVP for C#.
