Onion architecture compared to hexagonal

Question

Is there any difference between them (onion | hexagonal), from my understanding they are just the same, they focus upon the domain which is at the core of the application and sh

Answer 1

Previous answers make a fundamentally incorrect statement about Onion architecture. They assert "in Onion the UI and Data access are part of the same layer". The confusion might come from thinking all layers talk to everything above and below them.

In reality an Onion diagram is a poor representation of the Onion Architecture. The key takeaway is that the core domain layer is agnostic of any surrounding layers and the surrounding layers typically are also agnostic of each other. Usually this means that a UI talks to a Service which talks to Data and Domain layers. The UI doesn't directly interact with the other layers, and the layer interactions are abstracted by using Dependency Injection and Interface Segregation.

To my knowledge there aren't any architectural patterns that advise mixing Data Access and UI (some, such as Active Record, mix Business and Data Access). Seperately, there are technologies that produce code that avoids layers--rapid development tools often do this, but those are tools that favor speed to deployment over design and maintainability.

Onion, Hexagonal, and Ports and Adapters are in fact all different names for the same conceptual architecture.

Mark Seeman has a great post that helps clarify how the differences, if any, are marginal and semantic: Layers, Onions, Ports, Adapters: it's all the same