I've been thinking about where to best map Data Transfer Objects (DTOs) in my application. My understanding is that we should map models to DTOs to select only the necessary fields from the original model. I've read that this mapping is typically done in the service layer, but that doesn't feel right to me. Here's a rough example to illustrate my point. Let's say I have a class called `GenericModel` with several fields like `_a`, `_b`, `_c`, etc. The corresponding `GenericDTO` only includes `_a`, `_b`, and `_c`. If I use the service in a controller and want to return data, mapping in the service makes sense, but what if I want to use this service in another service class? If I map to DTO in the service, it restricts the data I can access elsewhere. I think the service should return the complete model and only map to DTO in the controller for client responses. What do others think about this approach?
5 Answers
In my previous job, we set up a system where we clearly defined layers: an API receiver that just translates requests, a coordinator that handles logic, and a service layer that does the actual work using database models. This way, you avoid directly intertwining your data flow with DTOs, and if you have to call services from other business logics, you can do so without restricting to a specific DTO format.
It sounds like you're on the right track. When you're using an ORM, the service layer really should avoid returning the ORM entities directly, because they're not tailored for transfer. DTOs are primarily about transferring data the way you want it, not just picking fields from models. Keeping data integrity while transferring is key, and yes, mapping done within the DAO layer often makes more sense than in the service layer. It gives you flexibility in how you handle data across various layers without being overly restrictive.
I'd say there's no hard and fast rule; it really depends on your application’s architecture. DTOs aren't tied solely to controllers. They can help simplify data transfer through your entire application. If your use case mostly involves returning data in a controller, then mapping there often makes the most sense. But be careful not to over-complicate things by creating multiple DTOs for different layers unless necessary. Generally, wherever you find it convenient is a good spot to map, as long as it keeps your architecture clean.
Exactly! As long as you keep an eye on how the application is structured, mapping at the right boundary works well.
The key takeaway here is to remain flexible and not overly rigid about where you do your mapping. DTOs should essentially help you facilitate data transfer, so it’s okay to adjust their use based on the context of your application as it grows.
I like that approach! Keeping it flexible can save a lot of headaches in the future.
I think avoiding DTOs in your domain logic is a solid principle. Let your domain services operate on models and only map to DTOs when interacting with the API or client. This way, your services remain modular and reusable without being tied down by the specifics of what has to go back to the client. If you need a specific projection for certain queries, that's when you can create dedicated queries for those DTOs.
Yes! It keeps services versatile since they can be used in multiple scenarios.
Totally agree! It feels cleaner to separate your data handling from your API logic.