CQRS – key concepts and best practices

Conceptual Understanding

1. Onion Architecture is all about the positioning of concerns and flow of dependencies, primarily toward the center.
2. The center of the onion, the domain model, should have no dependencies on any outer layers.
3. Layers in the Onion Architecture are differentiated based on their responsibilities.
4. The layers include: Domain Model (center), Domain Services, Application Services, and Infrastructure (outermost).
5. The inner layers define interfaces that outer layers implement.
6. Dependency inversion is used to invert the flow of control which helps in achieving a decoupled and testable architecture.
7. Onion Architecture emphasizes that the infrastructure is just a detail and the application should not be dependent on it.
8. The architecture helps in building scalable, maintainable, and testable applications.

Domain Layer

9. This is the innermost layer representing enterprise-wide business concepts.
10. It includes Entities, Value Objects, and Domain Events.
11. It is technology-agnostic and has no dependencies on outer layers.
12. Contains business rules that should be common to multiple applications in the same domain.
13. Defines interfaces for repositories that outer layers