Make sure that you have gone through my article about CQRS for ASP.NET Core before proceeding. To keep things simple but demonstrate the architecture to the fullest, we will build an ASP.NET Core Web API that is quite scalable. For this article, Let’s have a WebApi that has just one entity, Product.
Onion Architecture with .NET 6/.NET Core and CQRS/Event Sourcing following a DDD approach
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. Now, every application ideally has its own dedicated Database.
How the Layers Stack Up
- You can follow that article and add the Required Commands and Handlers to the Application Layer.
- In this article, we will cover the onion architecture using the ASP.Net 6 Web API.
- This will be an Empty API Controller which will have API Versioning enabled in the Attribute and also a MediatR object.
- This technique is described by Simon Brown in the clean architecture book, chapter «the missing chapter», page 318.
- After adding all the layers our project structure will look like this.
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. Conceptually, we can consider that the Infrastructure and Presentation layers are on the same level of the hierarchy. 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.
Next, we’ll create abstractions in the OnionArchitectureGuide.Application.Abstraction before implementing these contracts in the OnionArchitectureGuide.Application.Implementation. In the next post, we’ll start implementing Onion Architecture layer by layer. Let’s take a deeper look into the “Core” layers in each, to try and analyze the logical architecture and project structure.
Moreover, the Prototype Design Pattern has been employed to structure the creation of objects, ensuring a consistent and efficient approach to managing instances of the Article model. This design pattern facilitates the implementation of a flexible and reusable solution. You’ve successfully built a simple application using Onion Architecture. We’ve navigated through each layer, implementing the core logic and exposing it through an API. We should avoid using ApplicationDbContext, repositories, or service implementations directly in the API project. This is why all implementations have internal access modifiers.
- It basically has the models/entities, Exception, validation rules, Settings, and anything that is quite common throughout the solution.
- We are depending on abstractions at compile-time, which gives us strict contracts to work with, and we are being provided with the implementation at runtime.
- For the Domain layer, we need to add the library project to our application.
- Similar to the Application layer, we will have to create a new class just to register the dependencies and services of this layer to the service container.
- And since the Services.Abstractions project does not reference any other project, we have imposed a very strict set of methods that we can call inside of our controllers.
- By now it should be obvious that the Presentation project will only have a reference to the Services.Abstraction project.
Onion Architecture in .NET Core: Keeping Your Core Clean (Part
The outer layers of the architecture implement these interfaces. This means that in the Domain layer, we are not concerning ourselves with infrastructure details such as the database or external services. We can write business logic without concern about any of the implementation details. If we need anything from an external system or service, we can just create an interface for it and consume it. We do not have to worry about how it will be implemented. The higher layers of the Onion will take care of implementing that interface transparently.
Design Community
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. In the Infrastructure project, implement the repository. Nothing in an inner circle can know anything at all about something in an outer circle.
Looking forward to your next piece on Clean Architecture! Thanks for sharing your knowledge and starting this discussion. Application LayerHandles business use cases—like creating an order—but stays blissfully ignorant about where that order gets saved. In the Core project, define the CSharpCornerArticle model.
CQRS and Event Sourcing
Because the patterns are so similar, it’s hard to choose one. So far, things are looking very similar between the two architectural patterns. People often use the topics interchangeably for this reason. Notably, the outermost layers only depend on the inner layers, not the other way around. As we gradually ‘peel the layers of the onion,’ we expose the inner layers.
Implement Onion Architecture in .NET Core for Product Order Service
The typical layers include Core, Infrastructure, and Presentation. To achieve this, let’s create a new «Class Library (.NET Standard/.NET Library)» project named OnionArchitectureGuide.DependencyManager within the ‘Presentation’ solution folder. Then, add project references to OnionArchitectureGuide.Application.Implementation and OnionArchitectureGuide.Infrastructure to this new project. Clean architecture makes it easy to keep different business areas separate and extend them by explicitly exposing functionality through use cases, much like vertical slice architecture. On the other hand, onion architecture provides a clearer separation of concerns, which means it’s easier to extend the overall application.
If the latest JavaScript framework drops and everyone loses their minds, your business rules don’t flinch. No more pollution from infrastructure code sneaking into your logic. This implementation serves as a foundation for building robust, modular, and scalable ASP.NET Core Web APIs. As the project evolves, additional features, security measures, and optimizations can be incorporated while adhering to the principles of the chosen architectural style.
In case you want to implement email feature logic, we define an IMailService in the Service Layer. Using DIP, it is easily possible to switch the implementations. This is where one onion architecture .net core of the key differences in the patterns emerges. The clean architecture pattern attempts to organize code around use cases and has a real focus on business logic. The emphasis is placed on explicitly defining these use cases.