It creates a structure of layers, just like an onion, where you could test everything separately. Jeffrey Palermo coined the term “Onion Architecture” in 2008. This architecture enables greater application testability, maintainability, and dependability on infrastructures such as databases and services. Generally speaking, both the testability and loose coupling benefits of DI tend to outweigh most considerations, making the use of DI a default choice. From there, I came up to the conclusion that for the language patches I don’t want to extract implementations to the outer circle of the onion because it harms more than helps.

I can’t speak for every author but I have heard Robert Martin explain module to mean object if you happen to be in an object oriented context. Modularization is an older philosophy of designing so parts are easy to remove and swap. However, neither of these two services must become a part of the CoreUtils because both highly depend on the boundaries, our application works within. 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. It might be replaced by single statement “you should only use pure functions respecting dependency rule” but explicit list seems more descriptive to me. It is obvious that everything placed in the CoreUtils become carved in stone for an application.

Department Service

It can be hard to implement a service using Onion Architecture when you have a database-centric background. The change in paradigm is not so straightforward, so you will need to invest some time in learning the architecture before you can use it effortlessly. The Infrastructure Layer should not implement any business logic, as well as any use case flow. A Domain Service contains behavior that is not attached to a specific domain model.

This is how you can invert the dependencies to build scalable applications. In this article, We will talk about Onion Architecture In ASP.NET Core and its advantages. You can find the source code of this implementation on my GitHub. 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.


A while back we looked at layered architecture and how it can still be a good approach for some applications. If you require wedged or diced onions, you should start with a cut through its root and that top thing that sticks out and grows when you don’t use the onion fast enough. However, if you require an architecture analogy, you slice it horizontally through the center.

But precisely what is Onion Architecture, on which principle it is based, what is the essence of Onion Architecture, when to implement it, etc., will be discussed in this article. Just because you should rely on DI across bounded contexts, does not somehow imply that you’re not allowed to rely on DI within a bounded context. When organized like this the assumption is that the inner stuff is more stable than the outer stuff. DIP lets you strip off the outer stuff and add new outer stuff without breaking the inner stuff.

Constructing the Onion

It comes with several principles and layers that will be explained below. In core, you will have repositories talking to DAL and domain models, and services (not web services) onion architecture dealing with repositories and domain models. The Model is used to move data between the View and the Controller, where the business logic executes any operations.

onion layer architecture

The domain service layer defines domain-specific events. These are events that your service layer will define interfaces for, like completing orders, shipping orders, returning orders, and so on. The Domain entities in the center represent the business and behavior objects.

Advantages of Onion Architecture

The actual type of database and the way of storing data is determined at the upper infrastructure level. The popularity of microservices is growing due to the range of benefits they offer to developers and businesses. 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.

onion layer architecture

It’s easier to maintain an application that has a good separation of concerns. We can write business logic without concern about any of the implementation details. If we need anything from an external system or service, we can just create an interface for it and consume it.

Domain services

Few of the solutions developed and maintained by Microsoft MVPs like eShopOnWeb and eShopOnContainers also follow a similar (slightly more complicated variant of this approach). We will do a simple test to ensure that our solution works. I will just create a new product and make a request to query all the existing products as well. You can see that we are adding the API Versioning data to the route attribute and also creating an IMediator object.

onion layer architecture

Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. Hope this article helps you in a clear understanding of Onion Architecture. This contains the Core Business Logic as part of our project which acts as a layer between the Repositorylayer and Controller. The rule here is a layer cannot use nothing from above layer. As per my understanding I have drafted a small presentation and attached as an image in this post.

What are the Layers of the Onion Architecture?

For this article, Let’s have a WebApi that has just one entity, Product. We will perform CRUD Operations on it while using the Onion architecture. To maintain structural Sanity in Mid to Larger Solutions, it is always recommended to follow some kind of architecture. You must have seen most of the Open Sourced Projects having multiple layers of Projects within a complex folder structure.