We will add the interfaces that consist of the data access pattern for reading and writing operations with the database. Each layer/circle encapsulates or hides internal implementation details and exposes an interface to the outer layer. All layers also need to provide information that is conveniently consumed by inner layers. The goal is to minimize coupling between layers and maximize coupling within a vertical slice across layers.

Basically, these 5 Classes would cover our CRUD Operations implementation. Make sure that you have gone through my article about CQRS for ASP.NET Core before proceeding. Maybe an Entity Framework Core Layer for Accessing the DB, a Layer specifically made to generate JWT Tokens for Authentication or even a Hangfire Layer. You will understand more when we start Implementing Onion Architecture in ASP.NET Core WebApi Project.

Microservices

Aliaksandr is a Senior .NET developer at SaM Solutions with 13 years of experience. Being a Microsoft certified engineer, he specializes in web development and has experience what is onion architecture in creating desktop and mobile solutions. Aliaksandr is fond of learning new technologies, conducting meetups and teaching newbies at internal company courses.

The difference between clean and sustainable code is that the former can be updated and maintained throughout time, while the latter is simple to read, comprehend, and edit. Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context. 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.

Clean Architecture and Onion Architecture

It is responsible for coordinating the interaction between the Domain layer, the Infrastructure layer, and the User Interface layer. The Application layer defines the use cases of the application and implements the business logic using the services and interfaces provided by the Domain layer. This is the more important over these architectures, then if for onion the object for coordinate from user interface input to infrastructure, domain etc..

• And finally, we saw how our Presentation layer is implemented as a separate project by decoupling the controllers from the main Web application.
• Onion architecture consists of several concentric layers interacting with each other towards the core, which is the domain.
• The Domain layer, which contains the business logic, can be easily tested without the need for the Infrastructure layer or the User Interface layer.
• In cases where there is both a physical and logical separation of concerns, it is often referred to as n-tiered application where n is the number of separations.
• Using the code first approach in the application development using Asp.net core these entities are used to create the tables in the database.
• It can be a web application, a mobile application, or a desktop application.

Additionally, the onion architecture can improve performance by allowing components to be reused and reducing the amount of duplication. An effective design pattern for writers of clean, long-lasting code is onion architecture. The Onion Architecture helps to guarantee that each layer has a distinct duty and is isolated from the other layers by grouping concerns into various layers.

Dependency

Let’s consider the use case to create an order with a list of items. We first need to calculate the price including tax computation/discounts, etc., save order items and send order confirmation notification to the customer. The application services can be only invoked by Infrastructure services. Onion Architecture is comprised of multiple concentric layers interfacing with each other towards the core that represents the domain. The architecture does not focus on underlying technology or frameworks but the actual domain models.

By doing dependency injection in all the code, everything becomes easier to test. If you have a repository that expects a PostgreSQL client, the main should instantiate it and pass it to the repository during its initialization. The application’s entrypoint (usually, the main) should be responsible for instantiating all necessary dependencies and injecting them into your code. The inner layers shouldn’t know if your application is being exposed through an API, through a CLI, or whatever.

What is Onion Architecture?

The big drawback to this top-down layered architecture is the coupling that it creates. Each layer is coupled to the layers below it, and each layer is often coupled to various infrastructure concerns. However, without coupling, our systems wouldn’t do anything useful, but this architecture creates unnecessary coupling. This layer creates an abstraction between the domain entities and business logic of an application. In this layer, we typically add interfaces that provide object saving and retrieving behavior typically by involving a database. This layer consists of the data access pattern, which is a more loosely coupled approach to data access.

Onion architecture is a conceptual model for structuring software. Its intention is to isolate the core domain logic of an application from the surrounding concerns, such as the user interface or data access. Microservices and Domain-driven design are two different things but they come hand in hand while implementing microservices.

Domain Model

And the most challenging task was to find a balance between all these functions. The main issues we faced were related to maintaining the low connectivity of microservices. That’s why it was difficult to immediately divide the functionality into the necessary microservices.

It lets a specific team or individual work on a particular layer without disturbing the integrity of the others. It makes it much easier to track changes using source control. And, more expert developers may have differing opinions or they have additional rules or principles that they discovered to be very helpful during the development and implementation phase. Therefore, if there are corrections to be made, do leave a comment below and I will update the information here. This way, all of us get to benefit and improve the general quality of software.

Epstein Family Amphitheater, UC San Diego (Orchid for Public Architecture)

The architecture is named Onion Architecture because it has several layers around the core of the application, just like the layers of an onion. The core of the application contains the business logic and is independent of the infrastructure and the user interface. The infrastructure and user interface layers depend on the core layer. Domain services are responsible for holding domain logic and business rules. All the business logic should be implemented as a part of domain services.