The Onion Architecture : part 1 Programming with Palermo

It’s a good fit for microservices, where data access layer not only comprises database, but also for example an http client, to get data from another microservice, or even from an external system. Onion Architecture solved these problem by defining layers from the core to the Infrastructure. It applies the fundamental rule by moving all coupling towards the center.

• Inside the v1 Folder, add a new empty API Controller named ProductController.
• Using this approach, we can encapsulate all of the rich business logic in the Domain and Service layers without ever having to know any implementation details.
• To do so, we must expose only immutable objects, preventing misuse of the API to gain domain access.
• In this article, we will learn about an approach with which we will build a SUPER-FAST Repository Implementation using all the latest libraries and concepts….
• The number of layers in application will vary but domain is always at the center.
• See the beauty of loose coupling achieved using this architecture.

C# programmers are drawn to Onion Architecture due to the dependency flows. If you are interested in learning more C# while working with the Onion Architecture, visit the TechRepublic Academy. The basic principle of Onion Architecture is to follow the boundaries of these layers – the inner layer can’t depend on its outer layer but can depend on layers beneath. For example, domain layer can’t depend on Infrastructure layer, but Infrastructure layer can depend on Domain layer. Imagine if you put the saveObjectToDatabase method in domain object, then you will depend on Infrastructure layer which is a violation of Onion Architecture.

UI Layer

The Onion architecture was first introduced by Jeffrey Palermo, to overcome the issues of the traditional N-layered architecture approach. Let’s understand different layers of the architecture and their responsibilities with an order creation use case. Low coupling in which one module interacts with another module and does not need to be concerned with the other module’s internals. All the internal layers need not be concerned about internal implementation of external layers.

The entities defined in the Domain layer are going to capture the information that is important for describing the problem domain. Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects. The Onion architecture is also commonly known as the “Clean architecture” or “Ports and adapters”. These architectural approaches are just variations of the same theme. In this article, we are going to learn about Onion architecture and what are its advantages. We will build a RESTful API that follows the Onion architecture, with ASP.NET Core and .NET 5.

Generate the Migrations and the Database

The
infrastructure has all the framework — in this case Spring Boot — database driver, and other dependencies, and itself
depends on both domain and application. There’s of course nothing preventing you from declaring extra dependencies,
say Lombok. The most important thing to note here is that with this build setup, it will not be possible to reverse the
order of dependencies between the layers. In other words, if your application has several lines of code in button_submit or page_load events and if it’s doing several things in one single method, then it’s a matter of concern. Because sooner or later system will change and new developers will keep adding new business logic to these existing events, and the eventual situation would be very chaotic.

So metimes different design approaches try to achieve similar objectives. When we think about software architecture design, especially in the object-oriented world, the three most talked about patterns are Clean Architecture, Hexagonal Architecture, and Onion Architecture. Database Independent – Since we have a clean separation of data access, it is quite easy to switch between different database providers. This will be an Empty API Controller which will have API Versioning enabled in the Attribute and also a MediatR object. We will not have to re-define the API Versioning route or the Mediator object.

Implementation of Onion Architecture

Based on the DDD model, we’ve created onion architecture (aka hexagonal or clean architecture). In the Services.Abstractions project you can find the definitions for the service interfaces that are going to encapsulate the main business logic. Also, we are using the Contracts project to define the Data Transfer Objects (DTO) that we are going to consume with the service interfaces. Onion architecture might seem hard in beginning but is widely accepted in the industry.

Out on the edge, we would find a class that implements a repository interface. This class is coupled to a particular method of data access, and that is why it resides outside the application core. This class implements the repository interface and is thereby coupled to it. Each layer/circle encapsulates or hides internal implementation details and exposes an interface to the outer layer. All layers also need to provide information that is conveniently consumed by inner layers.