The Key Differences Between Onion Architecture and Clean Architecture

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. In software development, architecture plays a critical role in determining the quality, scalability, and maintainability of a software system. One of the most popular architectural patterns that have gained significant popularity in recent years is Onion Architecture. Then we saw how the Service layer was created, where we are encapsulating our business logic.

We can understand how this is being used in the application to follow DDD. This Domain Service is a process (checkout) which is not the responsibility of the domain model itself and it is adding an operation to the model (Purchase Aggregate Root). You may think where the implementation of that Repository Interface may reside. Jeffrey Palermo mentioned that out on the edges we see UI, Infrastructure, and Tests. The outer layer is reserved for things that change often. These things should be intentionally isolated from the application core.

WebAPI Boilerplate 🔥

DDD implies that you distinguish a certain bounded context, which is a set of entities tightly connected with each other but minimally connected with other entities in your system. In fact, while there are numerous definitions of microservices, there is no single clear and unified definition. Broadly speaking, microservices are web services that create a type of service-oriented architecture. Let’s create the table in SQL using the migration commands.

It makes it easier to modify and extend the codebase, identify and fix issues, and reuse components across different applications. However, we are going to do something different from what you are normally used to when creating Web APIs. By convention, the controllers are defined in the Controllers folder inside of the Web application. Because ASP.NET Core uses Dependency Injection everywhere, we need to have a reference to all of the projects in the solution from the Web application project. This allows us to configure our services inside of the Startup class. Using dependency inversion throughout the project, depending on abstractions (interfaces) and not the implementations, allows us to switch out the implementation at runtime transparently.

Tips To Write Clean Code

🔔 Note that some front-ends, such as native OSX or Android applications, are not part of the ui layer shown, encapsulated in deployable spring boot app. However, they are part of the Onion Architecture, and as such depend on the infra-api layer. Notice, onion architecture software here all the technology that can be swap in the future is not explicitly implemented here. Not even the HttpClient, it’s used an abstraction INetworkClient. This layer should interact with the Application Core services using the abstractions.

Let’s look at one of the most popular Architecture in ASP.NET Core Applications. Here is a simple diagrammatic representation of a variation of the N-Layer Architecture. 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.

Implementing MediatR for CRUD Operations

Figure 2 below outlines the domain within the application structure. Onion architecture is the division of an application into layers. Moreover, there is one independent level, which is in the center of the architecture. The second level depends on this level, the third depends on the second, and so on. That is, it turns out that around the first independent level, the second dependent is layered.

If executed well, the benefits will supercharge productivity and greatly increase the flexibility of the applications being developed. It also exchanges data with the infrastructure layer in order to read and write data. Also, this layer offers an API that the infrastructure layer can leverage to obtain business needs, and it is in charge of turning those requirements into usable code. Giving software projects a distinct structure and a separation of concerns, onion architecture can aid in achieving these objectives. This is how you can invert the dependencies to build scalable applications. Onion Architecture promotes maintainability, supports testing, and enables loose coupling and separation of concerns.

Separation of concerns

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Formatting of the dates to user then remains totally unaffected by the decision made by the technical team working on the API. Instead, it may be driven by aesthetic feelings of the customer as well as by necessity to display dates in a timezone of user choice. You may want to do adding/subtracting on dates, formatting the dates to human-readable form, formatting the dates to API-readable form, parsing the dates.

Onion Architecture in ASP.NET Core

When working with Onion Architecture, you should always start developing the inner layers before the outer ones.So, you should start by modeling your domain layer, instead of the database layer. Its intention is to get rid of transitive dependencies (with explicit focus on dependency from UI to DB). It is doing so by applying the dependency inversion by same principles, described in the ports and adapters. Interfaces are defined in the application core and implemented by the application boundary adapter. 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.

• This layer consists of the data access pattern, which is a more loosely coupled approach to data access.
• This architecture follows the Dependency Inversion Principle as well as Domain-Driven Design DDD.
• In this article, I will tell you about my experience of using onion architecture with a harmonized combination of DDD, ASP.NET Core Web API and CQRS for building microservices.
• Great, we have seen how to implement the Presentation layer.
• The UI cannot function if the business logic is not available.

The Onion Architecture is centered around the principle of dependency inversion and emphasizes modularity, testability, and maintainability. It promotes the separation of concerns by dividing the application into layers, each with its own specific responsibilities. An effective design pattern for writers of clean, long-lasting code is onion architecture.

Service Layer

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 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. In onion architecture, we have the domain layer, repository layer, service layer, and presentation layer. Onion architecture solves the problem that we face during the enterprise applications like coupling and separations of concerns.