SOLID in a layered / Clean Architecture solution — SOLID Principles with Examples

8. SOLID in a layered / Clean Architecture solution

AdvancedMediumLesson 8 of 8

src/
  Shop.Domain/          entities, value objects, domain interfaces  (no dependencies)
  Shop.Application/     use cases, IOrderRepository, IEmailSender    (→ Domain)
  Shop.Infrastructure/  EF Core repos, SMTP sender, Azure Blob        (→ Application)
  Shop.Api/             controllers, DI composition root              (→ Application, Infrastructure)

DIP: Application defines IOrderRepository; Infrastructure implements it. Dependencies point inwards.
SRP: one handler per use case (PlaceOrderHandler), e.g. with MediatR or plain classes.
OCP: cross-cutting concerns as decorators/pipeline behaviours (logging, validation, caching) without editing handlers.
ISP: small ports (IClock, ICurrentUser, IFileStore).
LSP: every IFileStore (local, Azure Blob, S3) behaves the same for callers.