This is another thing I wanted to promote with my team (and also more teams). When designing a distributed architecture I think that CQRS (Command Query Responsibility Segregation) and ES (Event Sourcing) can help a lot. Of course, they are not a Silver Bullet, they are just patterns that you can follow if your microservice needs it or not. It’s just a simple Onion Architecture with CQRS and Event Sourcing. You can use it as you want, you can create a GitHub repository using the template from there or just doing a fork/clone and creating the template from the dotnet CLI.

First, you need to create the Asp.net Core web API project using visual studio. After creating the project, we will add our layer to the project. After adding all the layers our project structure will look like this. And finally, we saw how our Presentation layer is implemented as a separate project by decoupling the controllers from the main Web application. Then, we explained how we can connect all of the layers using an ASP.NET Core Web API.

Step 7: Build and run application

This way anyone in the team mistakenly access the domain entities instead of the corresponding DTO. This layer is used to communicate with the presentation and repository layer. The service layer holds all the business logic of the entity. In this layer services interfaces are kept separate from their implementation for loose coupling and separation of concerns. The main purpose of this layer is to handle data access, external API integrations, and other infrastructure-related concerns. Since this is a simple implementation, we will only focus on data access and Repository implementation.

We will also together build a WebApi that follows a variant of Onion Architecture so that we get to see why it is important to implement such an architecture in your upcoming projects. You can find the source code of this implementation on my GitHub. Now we need to add a new project to our solution that will be the service layer.

Although very similar, we highlighted some nuances that can help us decide which one to choose when building our next application. Like with any architectural decision, it’s important to understand all the trade-offs as well as the reason behind applying the pattern. Hopefully, this article has helped to make that decision in the future. Because clean architecture strictly adheres to its guidelines, it might suit teams onion architecture .net core accustomed to such rules. This structure helps new developers integrate easily and reduces the chances of breaking established patterns. However, this adherence comes at the cost of flexibility.

Now, let’s look at some of the custom exceptions that we have inside the Exceptions folder. These are just some of the examples of what we could define in the Domain layer. We can be more or less strict, depending on our needs. We have to realize that everything is a tradeoff in software engineering.

Search code, repositories, users, issues, pull requests…

• Because the patterns are so similar, it’s hard to choose one.
• The business domain of the app gravitates around the pricing and purchase of items available at the supermarket.
• This layer is used to communicate with the presentation and repository layer.
• The emphasis is placed on explicitly defining these use cases.

In particular, the name of something declared in an outer circle must not be mentioned by the code in an inner circle. Application interface methods will typically be called from a controller in the WebApi Infrastructure layer to perform an action on its behalf. A key tenet of Onion Architecture is that dependencies flow inwards or laterally toward the core. Concretely this means a project that is in an outer layer can refer to a project in an inner layer or the same layer. A project should never refer to a project that is farther from the core than itself. Create a service interface and a service class in the OnionArchitectureDemo.Core project.

• This allows us to easily switch out data access implementations or integrate with different external systems without affecting the rest of the application.
• This file holds all the configurations required for the app launch.
• That would be insane from the maintainability point of view.
• There are quite a lot of improvements and fixes along the way from the day I started out.
• This line of code will find all of the controllers inside of the Presentation project and configure them with the framework.

Setting Up EF Core on the Persistence Project

We will start off by creating a Blank Solution on Visual Studio. PS, I use Visual Studio 2019 Comunity which is completely FREE. Domain and Application Layer will be at the center of the design. 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. Any small change in the Business Logics layer or Data access layer may prove dangerous to the integrity of the entire application.

Step 5. Infrastructure – Implement Repository

You can see that we are adding the API Versioning data to the route attribute and also creating an IMediator object. In the Startup/ConfigureServices of the API project, add these lines to register the Versioning. Then, run the following commands to add migrations and to generate/update the database. In the Application Layer, Create a New Folder called Features. This will have all the logic related to each Feature / Entity. Under this folder, add a new one and name it ProductFeatures.

Implementation of Onion Architecture

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.

However, in the OnModelCreating method, we are configuring our database context based on the entity configurations from the same assembly. The interesting part with the ServiceManager implementation is that we are leveraging the power of the Lazy class to ensure the lazy initialization of our services. This means that our service instances are only going to be created when we access them for the first time, and not before that. Testability is very high with the Onion architecture because everything depends on abstractions. The abstractions can be easily mocked with a mocking library such as Moq. To learn more about unit testing your projects in ASP.NET Core check out this article Testing MVC Controllers in ASP.NET Core.

Sponsor this project

Using dependency inversion throughout the project, depending on abstractions (interfaces) and not the implementations, allows us to switch out the implementation at runtime transparently. 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. Because it keeps your business logic clean and untouched by infrastructure chaos. If you’re switching from SQL Server to PostgreSQL, no problem.

Project Setup: Creating the Solution and Layers

I have already written a detailed article on MediatR and CQRS patterns in ASP.NET Core 3.1 WebApi Project. You can follow that article and add the Required Commands and Handlers to the Application Layer. The presentation layer is the default Asp.net core web API project Now we need to add the project references of all the layers as we did before. 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. But in the case of front-end applications, we present the data using the UI by consuming the APIS.