I'm a relatively new backend engineer with about 1-2 years of experience and I'm feeling a bit puzzled about the common advice that suggests keeping business logic out of controllers and in a separate service layer. I understand the idea behind reusability and the importance of having functions that can be called as needed, but if an endpoint is designed to perform a specific action that won't be repeated exactly elsewhere, why shouldn't the logic just be included in the controller itself? It feels like moving logic out of the controller might just be an unnecessary step with no added value since the service function is tailored to that specific endpoint. Also, how do I choose between mocking the service function and writing an end-to-end test in this context? I'd really appreciate any insights on why using a service layer is considered better practice in this case.
1 Answer
When you cram business logic directly into controllers, it can lead to a messy, tangled code that’s hard to maintain. For instance, I've worked on a few MVC apps where logic was sprinkled across controllers, and when we needed an API version, we ended up duplicating logic instead of reusing it. By pushing logic into a service layer, you can share it between different controllers, like having one for standard web views and another for API responses, which keeps your implementation clean and tidy.
Interesting take! But if both controllers have unique logic, doesn’t that make the service layer less useful? I mean, if they’re really different, aren’t we just talking about utility functions at that point?