Onion Architecture in ASP NET Core

In order to analyze our sample application, we use a tool called Structure101 Studio. Structure101 Studio is a commercial tool which helps to visualize and organize large code bases in various programming languages. When we analyze the sample application with Structure101 Studio we see that the application is well structured. It contains no namespace or class tangles and no fat namespaces or classes. From a structural complexity perspective our application is in good shape.

This results in a loosely coupled design where the Application Core (comprised of Application + Services + Domain Layer) doesn’t have any dependency on data access layer/technologies. Please check my article about the inversion of control. Another big advantage, it’s very easy to write automated tests for everything in the Application Core layer, because the infrastructure is outside that layer. UI layer doesn’t have any direct dependency so it’s easy to swap out implementations. The Model is used to move data between the View and the Controller, where the business logic executes any operations. The Controller handles web requests via action methods and returns the appropriate View.

Setting up the Controllers

Infrastructure is visually broken into pieces, all of those are application boundaries. Other parts of outer circle (UI/Tests) are also application boundaries. Mark Seeman in the “Dependency Injection in .NET”, chapter 2, draw layers without something called “infrastructure”, effectively bypassing this piece of the software as well. He only focusing on analysis of data access as a crucial piece of infrastructure.

• Speaking of layers, you may have heard that Onion Architecture is an inversion of the layered architecture.
• Along the outer ridge of your onion is your infrastructure layer.
• Comparing this with the case of a linear N-Layer where in order to perform an integration you need to pass through the Presentation, you can feel that its easy.
• Outer rings implement interfaces, meaning all technology related code remains in the outer rings.
• The architecture places a particular emphasis on the use of interfaces to decouple components.
• Onion Architecture is based on the inversion of control principle.

Now, let’s look at some of the custom exceptions that we have inside the Exceptions folder. Notice that we are setting the CancellationToken argument as an optional value, and giving it the default value. With this approach, if we don’t provide an actual CancellationToken value a CancellationToken.None will be provided for us. By doing this, we can ensure that our asynchronous calls that use the CancellationToken will always work. Connect and share knowledge within a single location that is structured and easy to search.

Common Software Architectural Patterns in a nutshell

The Service layer sits right above the Domain layer, which means that it has a reference to the Domain layer. The Service layer is split into two projects, Services.Abstractions and Services. These are just some of the examples of what we could define in the Domain layer. We have to realize that everything is a tradeoff in software engineering. Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects.

UI – User interface will be MVC based and will only interact with Business APIs and will only responsible for displaying the data and sending the data back to BusinessAPIs. If i introduce interfaces, would it be comparable to ONION Architecture. How can i convert it to ONION Architecture without compromising the security, scalability and performance. It’s a software that any developer should be able to do improvements and fixes without worrying about breaking something under the hood. Any developer, familiar with the domain, should be able to understand the code, and easily know where to change things.Modifying the view layer should not break any domain logic. Modifying the database modeling should not affect the software’s business rules.

Flow of Dependencies

I’m just trying to implement something that I can use with smaller applications, because clearly Repo/UoW approach is overkill for some scenarios and not to mention more code to write. What I really don’t understand is how can you get a reference of
DbContext (defined in Infrastructure Layer) in Application Layer
through DI. In the Application Core, we have the Domain and Service. Here, for simplicity, we just have two layers in the Application Core. In essence, MVC resolves the separation of concerns problem, but the tight coupling problem remains. We have already discussed the advantages and challenges this architecture has addressed.

So then everything in your application is dependent on your database layer. That might seem like no big deal, but let’s consider how often companies and applications make changes to their database. They can go from having all the logic in stored procedures to having it all in their ORM. They could also change their database vendor, their ORM layer, or even go from a relational database to a NoSQL solution. And then it could all be switched back to RDBMS when you realize that NoSQL is there to solve a problem you don’t even have. And none of these changes have anything to do with your core business functionality.

Ensuring code quality and reliability

This way, you are able to keep the core of the application relatively simple; focused on business-specific operations without having to account for endless “what-if’s”. It is one of the most popular Architectures in ASP.NET Core Applications. In this architecture, the Presentation Layer generally holds the part that the User can collaborate with, i.e, WebApi, MVC, Webforms, etc.

As this layer is purely logical, it should be pretty easy to test it, as you don’t have to worry about mocking IO operations. In a Clean Architecture, the solution is designed with the Application onion layer architecture Core at the center and the UI and Persistence depending on the Core. To solve this problem, developers split this single project into multiple projects, each pertaining to a Single Responsibility.

The Key Differences Between Onion Architecture and Clean Architecture

Jeffrey Palermo proposed this approach called Onion Architecture on his blog 2008. However, Jeffrey liked to have an easy to remember name, which allows communicating the architecture pattern more effectively. The biggest offender (and most common) is the coupling of UI and business logic to data access. Business logic can’t function if data access isn’t there.

External notification Service, GRPC Server endpoint, Kafka event stream adapter, database adapters. Application services also referred to as “Use Cases”, are services responsible for just orchestrating steps for requests and should not have any business logic. Application Services interact with other services to fulfil the client’s request.

Understanding the difference between ONION and N-Layered architecture

Onion Architecture is comprised of multiple concentric layers interfacing each other towards the core that represents the domain. The architecture does not depend on the data layer as in classic multi-tier architectures, but on the actual domain models. We simply move all infrastructure and data access concerns to the external of the application and not into the center.