1. Decorators. See https://blog.ploeh.dk/2010/04/07/DependencyInjectionisLooseCoupling/ https://blog.ploeh.dk/2010/04/07/DependencyInjectionisLooseC... 2. Yes,

1. Decorators. See https://blog.ploeh.dk/2010/04/07/DependencyInjectionisLooseCoupling/ https://blog.ploeh.dk/2010/04/07/DependencyInjectionisLooseC... 2. Yes, you need a lot of model types (groups, layers). You need the view models, the database models, the business logic models, and possibly others. Sure, that's annoying at first because they're pretty much identical. That's fine though, because in that case you can just use AutoMapper or something similar. I have never seen a project where the various models didn't change independently in a short timeframe (weeks, months at the most).