Onion Architecture In ASP NET Core 6 Web API

Onion Architecture requires additional code to implement the layers of the application. This can result in increased code overhead and a larger codebase, which can make the application more difficult to maintain. The Domain layer, which contains the business logic, can be easily tested without the need for the Infrastructure layer or the User Interface layer. The Application layer can be tested using mock objects, which makes the testing process faster and more efficient. This layer is the bridge between external infrastructure and the domain layers. The domain layers often need information or functionality in order to complete business functionality, however they should not directly depend on these.

Therefore, we built a validation mechanism into the MediatR pipeline using Fluent Validation. At times, we had to move a particular functionality into a separate microservice if it appeared in many places in the system. On the contrary, if some functionalities were tightly connected, we had to combine microservices into one.

Controllers

All of the layers interact with each other strictly through the interfaces defined in the layers below. The flow of dependencies is towards the core of the Onion. We will explain why this is important in the next section. An Anemic Domain Model is a domain model that has no behavior, just data.

• At the center part of the Onion Architecture, the domain layer exists; this layer represents the business and behavior objects.
• Domain services are orchestrated by application services to serve business use-case.
• However, I have previously written a detailed article on CQRS implementation in ASP.NET Core 3.1 API.
• The application services can be only invoked by Infrastructure services.
• Order is an entity and has attributes like OrderId, Address, UserInfo, OrderItems, PricingInfo and behaviour like AddOrderItems, GetPricingInfo, ValidateOrder, etc.
• In Onion architecture, our layer communicates with each other using interfaces.

Figure 2 below outlines the domain within the application structure. 2.infrastructure.payment contains adapters to a payment system of our organization but it is in another bounded context. We use MakePaymentService (a domain service) to decouple the payment system from other part of this system. Having created a domain model and a web API, we needed to seamlessly connect them. In fact, while there are numerous definitions of microservices, there is no single clear and unified definition.

Why Microservices Are Good for Our Project

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. In this article, we will cover the onion architecture using the ASP.Net 6 Web API. Onion architecture term is introduced by Jeffrey Palermo in 2008. Onion architecture solves common problems like coupling and separation of concerns. Organising our application in layers helps in achieving separation of concerns.

We often don’t keep systems up-to-date because it’s impossible to do. If coupling prevents easily upgrading parts of the system, then the business has no choice but to let the system fall behind into a state of disrepair. This is how legacy systems become stale, and eventually they are rewritten. Instead of building a highly decoupled structure, we often end up with several layers that are depending on each other. This is something really bad in building scalable applications and may pose issues with the growth of the codebase.

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Although the API has access to the Domain and Core, it doesn’t know anything about the Infrastructure. To handle this, DDD requires that each language belongs to one application context. It defines a scope where a ubiquitous language can be used freely. This is the bottommost layer that can work directly with domain objects. Value objects are to be used to return immutable data or represent a state change in the domain. They handle injection of repositories into domain services that need them to function.

In order to complete its functions, the application layer communicates with the domain layer. Business rules enforcement, validation, and other essential features that form the application’s core functionality are the responsibility of the domain layer. It is simpler to test and maintain if the domain logic is kept apart from the other levels. Now we need to add the student controller that will interact will our service layer and display the data to the users. Add the Data in the domain that is used to add the database context class.

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For example, you have an interface OrderRepository in your domain layer and you could implement it using some orm framework (persistence infrastructure). Onion architecture consists of several concentric layers interacting with each other towards the core, which is the domain. The architecture does not depend on the data layer, as in a traditional three-tier architecture; what is onion architecture it depends on real domain models. Unlike human language, where words may mean different things depending on context, software does not handle ambiguity well. In this article, you will get to see a set of rules that have been very helpful for me when I apply onion architecture in my software projects. Every layer has their respective rules and are categorised as such.

Furthermore, the added complexity of defining contracts / interfaces and religiously enforcing them requires a strong understanding of the pattern. If executed well, the benefits will supercharge productivity and greatly increase the flexibility of the applications being developed. In this layer is where the majority of our business logic lives, it carries out the operations to turn A into B, input into output, egg into chicken. It achieves this through interacting with the final layer, the Domain Model layer which is the representation of the high level data objects we use. Outer layer data formats should not be used by inner layers. Data formats used in an API can vary from those used in a DB for persistence.

Software Architecture Styles Software Engineer Should Know

This type of architecture allows for easy expansion and modification of an application as new requirements arise. MVC is a design pattern that stands for Model-View-Controller. It’s a common choice for developers during their work on the design of web, mobile, or desktop applications. Many programming languages and integrated development environments support MVC architecture.

Overall, Onion Architecture is a useful pattern for developing software applications that are modular, easy to understand, and maintainable. It is particularly useful for complex applications that require flexibility and scalability. By following the principles of Onion Architecture, developers can create high-quality applications that meet the needs of their users and stakeholders. Our fare calculation depends on external services such as routing information and fare models. Interfaces for these are defined in the Domain Services layer — IFareRepostory and IRouteService.

Advantages of Onion Architecture in ASP.NET Core

To keep it clear, in the above diagram we can see that the presentation layer depends on the logics layer, which in turn depends on the data access and so on. It includes adapters for databases, UI, external services like RESTful, etc. It has access to all areas of the API, Domain, and Core, though generally most operations that access the Domain must do so through the API. The exception to this would be something like domain interfaces that contain infrastructure implementations.