Onion Architecture: Definition, Principles & Benefits

Onion Architecture is a clean architecture while N-Tier is not a clean architecture. If you see the below given diagram of N-Tier architecture, you will find there are 3 layer – Presentation, Business, and Data Access. User interacts with the app from the Presentation layer as it contains th UI. The Business layer contains the business logic while the Data Access layer interacts with the database.

Advantages of onion architecture

The code snippet, mentioned below is the BaseEntity class. It is an ASP.NET Core Web application in this sample but it could be a Unit Test or Web API project. It is the most external part of an application by which the end-user can interact with the application.

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The following is the code snippet for the context class. The Entities Domain layer is a core and central part of the architecture. So first, we create „OA.Data” project to implement this layer.

Advantages of onion architecture

The first layer around the Domain Model is typically where we would find interfaces that provide object saving and retrieving behavior, called Repository Interfaces. In this article, we have seen what is Onion Architecture and the difference between Design, Architecture pattern and Architecture Style. Project template will help us to quick start application. Main benefit of Onion architecture is higher flexibility and de-coupling.

Benefits of Onion Architecture

If executed well, the benefits will supercharge productivity and greatly increase the flexibility of the applications being developed. To pass the data from UI to a controller to edit a user, use same view model named UserViewModel. The UserController has an action method named EditUser, which returns the view to edit a user. As the concept of dependency injection is central to the ASP.NET Core application, we register context, repository, and service to the dependency injection during the application start up. Thus, we register these as a Service in the ConfigureServices method in the StartUp class as per the following code snippet.

Yes, onion architecture is well-known in the programming world, and many applications use its principles. You could say that it’s another approach to solving a business problem. The hexagonal-like architectures are helping to increase the longevity of software, effectively eliminating the coupling between the coded business knowledge and the technology. In a couple of posts I will share with you mimacom’s way of tackling Onion Architecture with Spring Boot. In this first part I will give you more insights about it through a github-hosted example showing a simple implementation of ShoppingList’s API’s. DDD is an approach where the main focus is on real business values more than on technologies, frameworks, etc.

Now, we create a UserProfile entity, which inherits from the BaseEntity class. The code snippet, mentioned below is for the UserProfile entity. Now, we create an User entity, which is inherited from BaseEntity class. The code snippet, mentioned below is for the User entity. This approach makes it possible to create a universal business logic that is not tied to anything.

Short Story Of The Hexagonal-like Architectures

This layer is often called crosscutting layer which handles tracing, logging and more. The number of layers in the Application Core will vary, depends on the project, but basically, it holds the business model, which includes entities, services, and interfaces. It contains the abstractions for operations to be performed in the infrastructure (data access, network calls…). As we can see, there is a bunch of translation from top to bottom and from bottom to top going on.

  • Inward moving, we encounter the Domain Services layer.
  • The core layer, being the central layer, doesn’t even know that your domain, API, and infrastructure exist.
  • Onions are a delicious vegetable and are a core ingredient in cuisines around the world.
  • In this article, we have seen what is Onion Architecture and the difference between Design, Architecture pattern and Architecture Style.
  • The Entities Domain layer is a core and central part of the architecture.

These interfaces should be focusing on the business meaning of that interface and not on the technical aspects. So the shape of the interface is directly related to the scenario it is used in the business logic. Outer rings onion architecture implement interfaces, meaning all technology related code remains in the outer rings. The outermost ring can reference external libraries to provide implementations because it contains only technology specific code.

If a process or domain layer couples itself with infrastructure concerns, it is doing too much and becomes difficult to test. Especially this layer should know close to nothing about infrastructure. Infrastructure is only a plumbing support to the business layer, not the other way around. Development efforts should start from designing the domain-code and not the data-access, the necessary plumbing should be an implementation detail.

In the very center , we see the Domain Model , which represents the state and behavior combination that models truth for the organization. Around the Domain Model, there are other layers with more behavior. The outer layer is like a separate part of the whole application logic. It doesn’t depend much on the previous layers, so you can easily swap databases and other details. The relationship between each layer is one way and follows the rule that outer layers can depend on inner layers but not the other way around.


It’s very powerful and closely connected to two other architectural styles—Layered and Hexagonal. Onion Architecture is more appealing for C# programmers than Java programmers. However, it’s up to the architect community to consider and argue in the discussion on whether or not to apply the architecture. Not easy to understand for beginners, learning curve involved. Architects mostly mess up splitting responsibilities between layers.

Advantages of onion architecture

Include all your DbSets and include any repository methods you want access to (SaveChangesAsync, FindAsync, etc…). This interface lives in your Domain layer, whereas the implementation of it lives in the Infrastructure layer . It is, in essence, no different from how you would get a reference to your self-built UOW if you had implemented an UOW/repo layer. You register your db context in your DI framework and then your service layer is able to have this context injected.

Flexibility – the outer layer is completely decoupled from application logic making it easy to swap peripherals including databases, external services or testing tools. This layer is used to communicate between the Repository layer and Main Project where it consists of exposable APIs. In this layer, the service interfaces are kept separate from their implementation for loose coupling and also the separation of concerns. This architecture ensures that the application core doesn’t have to change as User Interface and Infrastructure services.

Persistence layer code snippets

This project holds POCO class and fluent API configuration for this POCO classes. It can have access to both the database and UI layers. Having created a domain model and a web API, we needed to seamlessly connect them.

Why do developers use onion architecture?

For the School app, we may add an interface dealing with database operations for the entities like Student, Teacher and fees. This interface can be implemented in the outer Infrastructure Layer where the actual database operations are added. This is also creating the Dependency Inversion Principle. A primer on the clean architecture pattern and its principles Stability is a crucial aspect of application architecture. Learn how clean architecture can straighten out your dependencies and make an app that is built to last.

You can download the complete source code from my GitHub Repository. Could adding some more sautéed onions to your marinara sauce or adding some diced onions to your salad help lower your cholesterol? https://globalcloudteam.com/ Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available. Combine cooked onions with other vegetables for a healthy side dish.

Impressive Health Benefits of Onions

Upon first sight the layer model seems straightforward and easy to adopt. Unfortunately developers often take the layering literally. In Visual Studio and you can see this newly created database with just one table called “Students”. In the Onion Architecture there are separatable concentric layers of codes such that the inner most layer is fully independent to other layers. Mostly you have 3 layers in this architecture and these are – Domain, Application, and “Infrastructure + Presentation”.

N-Laired application is built around data access and other infrastructure. The application has this coupling, when data access, web services, etc. change, the business logic layer will have to change. We can see in that simple example that refactoring from a layered architecture to an onion architecture is not enough in order to get a true onion architecture. The newly introduced Core still has a dependency outgoing.