I've often participated in arguments discussions about whether thin models or thin controllers should be preferred. The wisdom of a thin controller is that if you need to test your controller in isolation then you need to stub the dependencies of your request and response. It also violates the single responsibility principal because the controller could have multiple reasons to change. Seemingly, the alternative is to settle on having fat models. This results in having domain logic right next to your persistence logic. If you ever want to change your persistence layer you're going to be in for a painful time. That's a bit of a cargo cult argument because honestly who does that, but it's also a violation of the single responsibility principal. One way to decouple your domain logic from both persistence and controller is to use the "repository pattern". Here we encapsulate domain logic into a data service. This layer deals exclusively with implementing