c# Onion architecture in net core API

I am salute your time and efforts to share articles. So can we use CQRS with small projects or it can work good with only big one. Just some question in my mind,thought you can give clear answer on them,because i was working on CQRS but the project was microservice and is very big. In other cases, like you have mentioned, go with Infrastructure.Twilio. This is if you want a really good separation of the implementations, as each Project will be generating a DLL.

.net onion architecture example

CQS also tends to imply immediate consistency between the read and write models, while CQRS often implies eventual consistency between the read and write models. These days we have a different idea of what should go in a layer than 30 years ago, and we are more careful about where we put domain logic, presentation logic, and so on. But the architectural principles are all essentially the same.

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The core project is the inner most layer of the architecture. All the external layers like infrastructure, web etc. will use and depend on the core layer. However core project does not depend on any other layers. Before closing my article – I’d like to leave you guys with one though – which is “loose coupling”.

  • We do not have to worry about how it will be implemented.
  • Using DIP, it is easily possible to switch the implementations.
  • We will do a simple test to ensure that our solution works.
  • So for this, we add a class named UnityConainerRegistration and register the dependencies.

A project should never refer to a project that is farther from the core than itself. I’ve included the Solution Explorer view to see the relationship between the logical and physical layers side-by-side. I’ll explain each of the layers by working my way from the inside out. The name Onion Architecture was originally coined by Jeff Palermo, but has since gone under lots of other pseudonyms. Ports and Adapters, Hexagonal Architecture and Clean Architecture are all different names for effectively the same thing. They represent a way to structure the code that clearly separates the domain of the problem from the underlying technologies that implement the solution.

These will include Controllers, Views, Pages, Filters, TagHelpers, Middleware, etc. If it has a dependency on ASP.NET Core packages, it probably belongs in this project. In addition, any DTO types you're using specifically to communicate over the wire such as ViewModels, API Models, and the like, should go here by default. There are reasons why you might want to define these in another project, such as if you're using Blazor WebAssembly and you want to share the DTOs between the client and the server. But by default they belong in the Web project until you find a good reason to move them. An app's composition root is where all of the services in the app's dependencies are defined and "wired up".

I have been hearing this too long and I always wondered what hexagonal, onion and clean architectures really mean. I…

This interface will be implemented on the Infrastructure layer and so EF codes does not fall under the Application Layer, but goes to the Infrastructure layer which is outside the core. How Onion Architecture differs from N-Tier architecture? Onion Architecture is a clean architecture while N-Tier is not a clean architecture. If you see the below given diagram of N-Tier architecture, you will find there are 3 layer – Presentation, Business, and Data Access. User interacts with the app from the Presentation layer as it contains th UI.

If you're following Domain-Driven Design, then this is where all of your domain model types belong. This will include entities as well as potentially value objects, aggregates, domain events, specifications, factories, and more. I'm a fan of using well-defined custom exceptions and guard clauses as well as custom validators, all of which would be defined in the domain model as well. In the Web app, you're going to have any and all of your ASP.NET Core and ASP.NET Core MVC types.

You mention that n-tier layers are tightly coupled, but that is not actually a requirement! It remains poor design no matter which architecture you think you’re using. It is equally possible to do “onion architecture” badly and tightly couple everything. In this article, We will talk about Onion Architecture In ASP.NET Core and its advantages.

Onion Architecture In ASP.NET Core 6 Web API

In Onion Architecture, dependencies go inwards, so my repositories know of my aggregates, but not the other way round. At the heart of our application is a single project with no dependencies. This is not a requirement of Onion Architecture, but it is a convenient way to divide our logic. These are the steps we need to follow to create a MVC application following to onion architecture. We have created the controller along with the view using the scaffolding.

.net onion architecture example

This is something really bad in building scalable applications and may pose issues with the growth of the codebase. 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. If you have been using Asp.net web forms to develop web application then adopting MVC architecture even fits better, because it provides the required framework to build web apps MVC way. But things doesn’t turn out as planned and leads to very tight coupling between UI and business logic and business logic to database logic.


Infrastructure layer will be independent of the Web layer, but will be dependent on the Core layer, for the POCO classes. This architecture term was coined by Jeffrey Palermoback in 2008. Long time since then and it has become very popular these days.

.net onion architecture example

When the job is executed, the changes have already been made, so we cannot throw an error when processing the job. The job must therefore be processed with a retry mechanism to ensure it completes. Writing to the read store can be done as part of the same database transaction to ensure consistency between the read and write sides.

A simple template for Onion Architecture with .NET 5

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. Application architecture is built on top of a domain model. Onion Architecture layers are connected through interfaces. Onion Architecture uses the concept of layers, but they are different from 3-tier and n-tier architecture layers.

Onion Architecture in .NET Core

In the Onion Architecture layers talk to each other using the Interfaces. Any concrete implantation would be provided to application at the run time. We’ve chosen MediatR to implement CQRS in the project. CQRS is a development principle claiming that a method must be either a command that performs an action or a request that returns data.

Better Testability – As the layers are more independent, it is easy to write test cases for each of the layers. Presentation Layer – This layer presents the UI of the application. The main purpose of Clean Architecture is to allow the business to adapt to changing technology and interfaces. WhiteApp or QuickApp API solution template which is built on Onion Architecture with all essential feature using .NET Core. You can call it as Domain-centric Architecture too.

If you have multiple Xamarin.Forms projects in one solution, they can both be here. Now we can test against any of the business onion architecture logic in our application with a mock layer. The same practice can be applied to test any other layer in the solution as well.

Events usually represent a change to the state of a domain entity. Entities and other domain objects are grouped together into clusters called aggregates, which provide a consistency boundary and can enforce the business rules of the domain. Once we’ve split everything up into boxes, we stitch it all back together again with some arrows.

Inside the v1 Folder, add a new empty API Controller named ProductController. Since this is a very basic controller that calls the mediator object, I will not go in deep. However, I have previously written a detailed article on CQRS implementation in ASP.NET Core 3.1 API. You could go through that article which covers the same scenario. We will have to register IApplicationDBContext and bind it to ApplicationDbContext, right?

The presentation layer is the default Asp.net core web API project Now we need to add the project references of all the layers as we did before. In the case of the API presentation layer that presents us the object data from the database using the HTTP request in the form of JSON Object. But in the case of front-end applications, we present the data using the UI by consuming the APIS. Using the onion architecture our application is loosely coupled because our layers communicate with each other using the interface. Let’s look at one of the most popular Architecture in ASP.NET Core Applications.


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