Onion Architecture In ASP NET Core With CQRS Detailed

But I think this can also lead to confusions, especially for new developers. If they only work with the abstractions, but the actual implementations are in a complete different place / layer. That’s why I pointed out, that with N-layerd architecture with facades, the abstractions would be in the same place as their implementations. Changes to one layer should not have an impact on the others because each layer is responsible for a distinct task.

Advantages of onion architecture

A crucial component of the Onion Architecture is dependency injection. Decoupling the layers is made possible, which makes it simpler to create unit tests and swap out components. There should be no external dependencies or technology-specific code at the domain layer.

A framework for giving feedback to others’ code

Similary, create another .NET Standard Library Project in the Core Folder. Do not forget to change the target version here as well. To clearly understand the advantages of Onion Architecture in ASP.NET Core Applications, we will need to study the issues with N Layer Architecture. It is one of the commonly used Solution Architecture amongst .NET developers. Note, I have chosen to call the most centre layer “Core” rather than Domain Models — a personal preference. Note — The following is my interpretation of this Architecture Pattern and may not be as intended by it’s publishers.

Advantages of onion architecture

The obvious advantage of the Onion architecture is that our controller’s methods become very thin. We moved all of the important business logic into the Service layer. There are more examples, but hopefully, you get the idea.


This is a infrastructure concern and should be handled by the application infrastructure. It can be a separate repo that creates external resources or a tool that lives in the application’s repo but runs before the application itself. https://www.globalcloudteam.com/ Database migration should be handled by your CI/CD pipeline. Your application code shouldn’t know nor care about such thing as the database schema version. This way developers can really learn how the onion architecture is implemented.

Let’s look at the one of the most popular Architecture in ASP.NET Core Applications. Here is a simple diagramatic representation of a variation of the N-Layer Architecture. Presentation Layer usualy 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. It holds all the logics related to the Business Requirement.

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This Domain Service is a process which is not the responsibility of the domain model itself and it is adding an operation to the model . 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.

  • In the Models folder, we will create the following database entities.
  • In this way we’ll end by hundreds of new architectures just by combining all OO Principals and Go4 patterns to the Entreprise Application Architectures.
  • We are hiding all the implementation details in the Infrastructure layer because it is at the top of the Onion architecture, while all of the lower layers depend on the interfaces .
  • Onion Architecture provides several benefits, including separation of concerns, testability, maintainability, flexibility, and scalability.
  • This will be an Empty API Controller which will have API Versioning enabled in the Attribute and also a MediatR object.

So, onion architecture is actually it’s own architectural pattern because you have different layers and your interfaces are in a different place… Or in other words, they are structured differently which is, by definition, an architectural pattern. The difference between N-layered architecture and Onion which I’ve noticed so far that you have a single place for contracts and it onion software architecture really helps you to follow Open/Close principle. And since the core layer shouldn’t be changed very often (ideally shouldn’t be changed at all) it helps you to pay attention to it during code-reviews. Performance overhead may result from the Onion Architecture’s additional layers and interfaces, particularly in applications that demand high-performance or real-time processing.

Implementing Onion Architecture in ASP.NET Core WebApi Project

Yes, you can definitely use Repository Pattern alongside Onion Architecture. It gives a better separation between your actual database of choice and your data access code. It depends on how organized you want your project to be and how comfortable you are with the patterns. You could either merge services like Twilio into a single Project layer and implement the interface within each corresponding folder. This is if you think the infrastructure implementation is not very complex. Using different projects for different layers is only ever coincidentally a good idea.

Advantages of onion architecture

Let’s understand different layers of the architecture and their responsibilities with an order creation use case. In the custom service folder, we will create the custom service class that inherits the ICustomService interface code of the custom service class is given below. Domain entities are the core and center of the architecture and have access to databases and UI Layer. Using the onion architecture our application is loosely coupled because our layers communicate with each other using the interface. Having created a domain model and a web API, we needed to seamlessly connect them.

C# versus C

You will understand more when we start Implementing Onion Architecture in ASP.NET Core WebApi Project. Then we saw how the Service layer was created, where we are encapsulating our business logic. We started with the Domain layer, where we saw the definitions for our entities and repository interfaces and exceptions.

Advantages of onion architecture

It consists of algorithms that are essential to its purpose and implement the use cases that are the heart of the application. Layers are not tightly coupled and have a separation of concerns. For every service, we will write the CRUD operation using our generic repository.

Adding The Entities to the Domain Project

Naturally, maybe you want to start the development by the database, but it’s a mistake! When working with Onion Architecture, you should always start developing the inner layers before the outer ones. They represent the business models, containing the business rules from it’s domain. With layered and hexagonal architectures understood, the time has come to talk about a relative – Onion Architecture, which puts a new spin on layers. We can understand how this is being used in the application to follow DDD.

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