MVC: Where to put business logic?
I prefer to put domain logic in the model for a couple of reasons.
The model should have no UI code in it and thus be easier to test. Whenever possible, I like to have a fully working (meaning complete test coverage) model before writing any UI code. The controller can trust that the model is doing the right thing and just deal with UI concerns.
If you put domain logic in a controller, it's not as easy to share between different apps, or even between different controllers.
I like to keep my models clean I.e. Just with properties and no business logic. I always think its good to inject dependencies into the controller and these dependencies contain the logic I perform on my models. I like to adhere to the single responsibility principle where possible and I find that models with tons of methods get bloated very quickly. There's pros and cons for both, injecting a lot of dependencies has an overhead yet allows to test in isolation and keeps classes simple and you'll end up having leaner controllers. Despite my logic not actually existing on my model as members of the class, its still business logic. I tend to not have business logic defined in the controller as mocking things like the Httpcontext are a bit of a nightmare and unnecessary.