Similar to other architectural styles like Hexagonal, Layered, Clean Architecture, etc. it provides a solution for common problems. The term “Onion Architecture” was first coined by Jeffry Palermo back in 2008 in a series of blog posts. The architecture is intended to address the challenges faced with traditional architectures and the common problems like coupling and separation of concerns. The modular and decoupled architecture that the Onion Architecture encourages makes it simpler to maintain the application over time. Developers can make changes to one layer without impacting the other levels since each layer has a distinct function and communicates with other layers through clearly defined interfaces.

The drawback of this traditional architecture is unnecessary coupling. We create a controller named UserController under the Controllers folder of the application. It has all ActionResult methods for the end-user interface of operations.

How to Migrate On-premise SQL Database to Azure

Usually it’s not a good idea to try to use a single repository for more than one aggregate, because maybe you will end up having a Generic Repository. It just contains data, and is used only in this use case as a return value. An Application Service is a piece of code which implements a use case. The Application Layer is the second most inner layer of the architecture. A Value Object is an object that has no identity, and is immutable.

I just wonder and want to know why all the samples we found with Entity framework? I have a big project to start and wish to write the logic in SQL stored procedures. Stored procedures because we find the easy maintenance and also easy to write the logic. And for this, wish to use ADO.Net without entity framework. Something that Steve smith mentioned in this post, All interfaces like services interfaces and repositories interfaces placed in inner center area of domain. Yes, you can definitely use Repository Pattern alongside Onion Architecture.

Benefits of an Onion Architecture

Now, we create action method, which returns an index view with the data. The code snippet of Index action method in UserController is mentioned below. We developed entity and context which are required to create a database but we will come back to this after creating the two more projects. It develops a loosely coupled application as the outer layer of the application always communicates with the inner layer via interfaces. So, onion architecture is actually it’s own architectural pattern because you have different layers and your interfaces are in a different place…

  • The modular layout favored by Onion Architecture makes it simple to scale the application.
  • But how would you account for these two different layers in your business layer?
  • That’s the reason why I am not going to explain software architectures as a war, trying to convince you which one is the best and why you should use it alone.
  • Could you perhaps elaborate a bit more on the issues concerning testing?
  • I have a full fledged Solution template that can get you started real easy.
  • All the business logic should be implemented as a part of domain services.

If you have very complex business logic, it would make sense to encapsulate it inside of our domain entities. But for most applications, it is usually easier to start with a simpler domain model, and only introduce complexity if it is required by the project. 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. The biggest offender is the coupling of UI and business logic to data access. However, the flexibility with technology upgrades doesn’t come handy with tightly coupled systems.

What is the motivation for splitting the Service layer?

Switchable UI Layer – Since we are keeping all the crucial logic away from the presentation layer, it is quite easy to switch to another tech – including Blazor. 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.

Benefits and Drawbacks of Onion Architecture

Next, let’s go to the Infrastructure Folder and add a layer for Database, . The presentation layer is where you would Ideally want to put the Project that the User can Access. No, Onion Architecture is a language- and framework-agnostic pattern that can be implemented using any programming language or framework. After Layered and Hexagonal architectures, the time has come to talk about their close cousin – the Onion Architecture initially introduced in aseries of posts by Jeffrey Palermo. I’ll propose a testing strategy for the hexagonal architecture. There are other similar architectures that uses some of the same principles.

Language and framework independent

Some companies that have successfully used Onion Architecture include Microsoft, Uber, and BBC iPlayer. They have used Onion Architecture to build scalable and maintainable software systems that can evolve and adapt to changing business requirements. Common pitfalls to avoid when implementing Onion Architecture include not separating concerns properly, creating tight coupling between layers, and not managing dependencies correctly.

Benefits and Drawbacks of Onion Architecture

ASP.NET Core is designed from the ground to support and leverage dependency injection. Thus, we create generic repository interface for the entity operations, so that we can develop loosely coupled application. The code snippet, mentioned below is for the IRepository interface. Now we create a second layer of the onion architecture which is a repository layer. To build this layer, we create one more class library project named OA.Repo.

Can Onion Architecture be combined with other architectural patterns?​

Here, the DefaultConnection is connection string which defined in appsettings.json file as per following code snippet. There are a ton of docs across the internet, however, if you use onion as much close to core principles as you can, then you feel much onion software architecture less pain at the end of the day. Then, we explained how we can connect all of the layers using an ASP.NET Core Web API. ExceptionHandlingMiddleware with the dependency container, we would get a runtime exception, and we do not want that to happen.

We create both IUserService and IUserProfile interface instances; then we inject these in the controller’s constructor to get its object. The following is a partial code snippet for the UserController in which service interfaces are injected, using constructor dependency injection. The layer is intended to create an abstraction layer between the Domain entities layer and the Business Logic layer of an application. It is a data access pattern that prompts a more loosely coupled approach to data access.

Middleware in ASP.NET Core

The number of layers in application will vary but domain is always at the center. The first layer around the domain is typically we would place interfaces that provides saving and retrieving behaviors, called repository interfaces. Out on the edges we see UI, Infrastructure and Tests. The outer layer is reserved for things that potentially changes often, these things are intentionally isolated from the application core.