The *Onion Architecture* is a software architecture proposed by Jeffrey Palermo. It is similar to the *Hexagonal Architecture* (Ports and Adapters) proposed by Alistair Cockburn.
Jeffrey Palermo proposed the Onion Arcitecture. It is similar to Alistair Cockburn's Hexagonal Architecture or Ports and Adapters.
The fundamental motivation of the approach is to avoid layer-to-layer dependencies usually associated with the N-tier architecture approach. This is achieved by placing all infrastructure, including databases, outside the problem domain.
According to Jeffrey Palermo:
The overall philosophy of the Onion Architecture is to keep your business logic and model in the middle (Core) of your application and push your dependencies as far outward as possible.
The problem domain is then completely independent of the required infrastructure (testing, databases, security, etc.). For example, this means that testing database accesses can be done thoroughly without a real database.
