This is also known as DIP or Dependency Inversion Principle. The Onion architecture, introduced by Jeffrey Palermo, overcomes the issues of layered architecture with great ease. With Onion Architecture, the game-changer is that the Domain Layer (Entities and Validation Rules that are common to the business case ) is at the Core of the Entire Application.

• For Example, Infrastructure layer implementations include external services used in Application Services and repositories used in the domain.
• In the very center we see the Domain Model, which represents the state and behavior combination that models truth for the organization.
• But in the case of front-end applications, we present the data using the UI by consuming the APIS.
• It represents the Web API or Unit Test project in a Web application.

The presentation Layer usually holds the Part that the User can interact with, i.e, WebApi, MVC, Webforms, and so on. Business Logic is probably the most important part of this entire setup. It holds all the logic related to the Business requirements.

Configuring the Services

You can now see the advantage of this kind of approach. Firstly, add a connection string to the appsettings.json onion architecture found in the WebApi Project. Now add a Product Class that inherits the Id from the BaseEntity.

Cloud services such as Microsoft Azure and database options including SQL Server and MSSQL are also frequently covered. 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. This architecture is undoubtedly biased toward object-oriented programming, and it puts objects before all others. At the center of Onion Architecture is the domain model, which represents the business and behavior objects. Around the domain layer are other layers, with more behaviors.

Start by modeling the database

Inside the v1 Folder, add a new empty API Controller named ProductController. Since this is a very basic controller that calls the mediator object, I will not go in deep. However, I have previously written a detailed article on CQRS implementation in ASP.NET Core 3.1 API. You could go through that article which covers the same scenario.

A Repository is a pattern for a collection of domain objects. The former are rules that are executed to implement a use case of your application. The latter are rules that belong to the business itself.

Repository Pattern

The Domain layer does not have any direct dependencies on the outside layers. The outer layers are all allowed to reference the layers that are directly below them in the hierarchy. It greatly depends on the complexity of the application and the size of the project to divide source code into multiple modules.

You can see the clear separation of concerns as we have read earlier. As mentioned earlier, the Core Layers will never depend on any other layer. Therefore what we do is that we create interfaces in the Application Layer and these interfaces get implemented in the external layers.

API Contract Testing with Postman

Now, every application ideally has its own dedicated Database. In order to access the Database, we introduce a Data Access Layer. This layer usually holds ORMs for ASP.NET to fetch/write to the database. It looks very similar to an onion with layers wrapping around a central core. Each of these layers represent a specific duty within the overall function of a service. In the case of the API presentation layer that presents us the object data from the database using the HTTP request in the form of JSON Object.

This file holds all the configurations required for the app launch. Thus, the swagger will open up by default every time you run the application. We will have to register Swager within the application service container. Navigate to ../Startup.cs and add these lines to the ConfigureServices https://www.globalcloudteam.com/ method. The presentation layer is where you would Ideally want to put the Project that the User can Access. In N Layer Architecture, the Database is usually the Core of the Entire Application, i.e It is the only layer that doesn’t have to depend on anything else.

Language and framework independent

Showcasing how the Polysemy library can be used to implement a REST application conforming to the guidelines of the Clean Architecture model. We have now set our expectations for anyone wishing to charge a user for a transaction within our Application Services layer. However, we are not doing anything useful at the moment with the transaction so from this and following the layers of Onion Architecture we need to define our Domain Services layer. Now we can see when we hit the GetAllStudent Endpoint we can see the data of students from the database in the form of JSON projects. We will follow the same project as we did for the Domain layer.

In this article, we have implemented the Onion architecture using the Entity Framework and Code First approach. We have now the knowledge of how the layer communicates with each other’s in onion architecture and how we can write the Generic code for the Interface repository and services. Now we can develop our project using onion architecture for API Development OR MVC Core Based projects. Infrastructure services also referred to as Infrastructure adapters are the outermost layer in onion architecture. These services are responsible for interacting with the external world and do not solve any domain problem.

Result Service

We are going to see why this is very useful later on when we get to the Presentation layer. 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. We will use the business domain of a Ride Sharing/Taxi Booking Application.