Where to put Entity To DTO transformation in a Spring boot project?

Question

I'm working on a spring boot (MVC, DATA, JPA...) + angular project.

I'm stuck between two options. Although, they both work without any problems.

It's just from an Architecture viewpoint which one is the best or which one is used most.

My question is where's the best way to do the transformation from Entity to DTO.

Option 1 : The one I'm implementing now.

I put the transformation in the controller. In my controller I call a service method to get a list of entities. And then, I do the transformation of a list of entities to a list of DTOs using a ModelMapper and return the result to the front.

Entity ==> Repository ==> Service ==> Controller ==> ModelMapper ==> Return DTO

• Pros : Service Layer will always return entities objects (reuse)

• Cons : A lot of code in the controller (in case I need to parse the list...)

Option 2 :

Put the transformation in the service layer.

So, instead of returning a list of entities, my service layer will return a list of DTOs.

Entity ==> Repository ==> Service ==> ModelMapper ==> Controller  ==> Return DTO

• Pros : Objects returned by the service will be returned directly to the front (not a lot of code in controller)

• Cons : I dont know ^^'

Answer 1

Following the clean coding principles, Service layer should do the conversion, but as it is conversion only and no business logic is involved, your controller can also do that. However I would do that in controller only, if conversion code isn't more than 3-4 lines of code. As it would make my controller look cluttered with code. Reference- https://www.baeldung.com/entity-to-and-from-dto-for-a-java-spring-application.

Answer 2

I believe better way of converting entity to DTO would be :

• If you don't really need entity in service, then convert entity to
  DTO on repository level only. Also if you're using Spring Data JPA,
  then you can directly convert entity to DTO without any extra code.
  But if you're writing your complex queries which can not be fulfilled by it, then you can convert it inside your repo implementation.
  Doing this will ensure that no services will ever get hold of data
  which it must not have. No sensitive data will be exposed.

• If you really need entity and there's no work around for it, then
  you can convert it to DTO in service layer as controller must never
  have data access which it should not. No sensitive data should ever
  be exposed to controller level. It's not a good design.

I think these are ways you can do conversion of entity to DTO, but the best design is to convert entity to DTO in repo itself.

I hope this helps you solve your problem.

Good luck!