In traditional architectures, the separation of components into distinct layers (such as controllers, services, data access layers, and utility/helper classes) aims to provide a clear structure. However, without proper guidelines or a cohesive architecture, these layers often lead to confusion about where specific types of logic should reside. This lack of clarity in defining responsibilities and boundaries for each layer results in several issues, ultimately contributing to the emergence of "God objects." Developers might face ambiguity about which layer should handle certain types of logic in such architectures. For instance, business logic might inadvertently find its way into controllers, while data access operations might sneak into services. This confusion in logic placement leads to a scattered codebase where responsibilities overlap, making it challenging to identify the appropriate location for implementing or modifying functionalities.
The emergence of new architectural patterns signifies the search for improved methodologies. Notably, Jimmy Bogard's involvement with Vertical Slice Architecture (VSA) marks a significant step forward.
Vertical Slice Architecture reimagines architecture by transitioning from horizontal layering to a feature-centric organizational model. Each feature or user story resides within its distinct slice, consolidating all layers – encompassing UI, business logic, and data access – into a cohesive unit. MediatR, a mediator pattern library, serves as a facilitator within this architecture. It assists in categorizing the overall process of serving a use case into three fundamental components: a Request object, a Handler Object, and a Response object. These components are coordinated and managed using MediatR to ensure efficient communication and handling within the Vertical Slice Architecture.
Vertical Slice Architecture also aligns seamlessly with the Command Query Responsibility Segregation (CQRS) principles. This alignment is particularly evident in how Vertical Slice Architecture emphasizes organizing code around specific features or user stories, mirroring the segregation of commands (requests that change state) and queries (requests that fetch data) inherent in the CQRS pattern.