Review domain is refactored

[kubazuch]

DDD plan

• code is separated into layers: API (controller), domain (model + service), infra (repository)
• layers communicate like: Controller -> Service -> Repository and ONLY like that.
• Service can use other Services, Repository can use other Repositories, Service can use only one Repository!
• If endpoint has a PUT edit endpoint, it should ideally also have a PATCH edit endpoint, where PUT takes whole object, and PATCH just some of the object fields.

API layer

• input data validation, conversion, etc. should be handled in Controller
• Controller can call Service, controller also uses Dtos and Mappers
• Controller is the only place in the app that knows about users as in their credentials and authorities
• Use Authentication authentication as parameter and authentication.getPrincipal() to get logged in User
• Use @...Mapping(params = ...) to separate logic depending on parameter

Domain layer

• Services return Model objects, there are no Dtos in any Service
• Exceptions are thrown in Services
• Thrown exceptions are semantic!

Infrastructure layer

• All SQL calls are prepared to do things in the DBMS
• No tolerance for situations such as getting huge amounts of data from database just to filter it in backend