c# Onion architecture in net core API

Today, we will discuss Onion Architecture which is also said to be a cousin of layered and hexagonal architecture. The web world is a collection of various traditional architectures. Each of these pieces of architecture has its pros and cons.

onion layer architecture

PS, I use Visual Studio 2019 Comunity which is completely FREE. 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 most commonly used Solution Architectures amongst .NET developers.

Presentation Layer

You will understand more when we start Implementing Onion Architecture in ASP.NET Core WebApi Project. The Onion architecture, introduced by Jeffrey Palermo, overcomes the issues of layered architecture with great ease. With Onion Architecture, onion architecture the game-changer is that the Domain Layer (Entities and Validation Rules that are common to the business case ) is at the Core of the Entire Application. In this approach, we can see that all the Layers are dependent only on the Core Layers.

Our customer needed a software system compatible with their hardware so that clients could buy equipment, install software and create and manage content. The challenge was to create a cloud software solution for a digital signage hardware manufacturer. There are multiple interfaces, making it easy to get lost in the whole mix. As a result, you’ll waste a lot of time figuring which interface to use. Another helpful tool to implement dependency governance is NsDepCop. 1 It looks OK but I am not sure it’s a good idea to insert dependency resolution into the diagram.

Benefits and Drawbacks of Onion Architecture

Code should depend only on the same layer or layers more central to itself. Click on project reference now and select the Domain layer. After Adding the DbSet properties we need to add the migration using the package manager console and run the command https://www.globalcloudteam.com/ Add-Migration. When working with Scrum, you will probably want to break the development of the software into different tasks, so it can be done by different people. This anti pattern has a lot of problems which are well described in Fowler’s article.

onion layer architecture

This library provides almost limitless opportunities for setting data validation rules. It is well compatible with CQRS due to pipeline behaviors. But it does not quite solve the validation problem, especially if you need to take information from a database or from another microservice.

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I understand that the focus of Onion architecture is more on flow of dependencies rather on how the layers interact with each other. But I found that domain entities are still accessible in the presentation layer (API layer). We cannot define it as internal because the entities will not be accessible by the application layer.

onion layer architecture

The flow of dependencies is towards the core of the Onion. We will explain why this is important in the next section. Like the Onion Architecture, the layered approach requires coupling from one layer to another. However, with the layered approach, your database ends up being the base of your application.

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But eventually, this problem was practically eliminated. Bounded context is a good fit for a microservices architecture. It is much easier to build a microservice around a bounded context. Onion architecture comes with very clear rules about priorities, dependence, and layers. Due to their clarity, you will always be able to understand which part relies on which layer. If you decide to implement onion architecture in your application, you’ll get multiple benefits.

onion layer architecture

Now that I’ve gotten that out of the way, let’s look at the various layers of the Onion Architecture. Most descriptions start on the outside, but I’d like to start in the middle. That’s the most important part of our onion and everything else builds on top of it. In addition, the onion architecture itself introduced certain problems. It took us some time to distribute functional parts between appropriate layers.

Start by modeling the database

However, it’s up to the architect community to consider and argue in the discussion on whether or not to apply the architecture.

  • His goal was to remove the problems that more common architectural practices, like the layered architecture, faced.
  • I’m not sure if that’s an Onion Architecture already, it depends on your interpretation.
  • This library provides almost limitless opportunities for setting data validation rules.
  • It creates a structure of layers, just like an onion, where you could test everything separately.
  • I have added the XML file to the root of the API Project.
  • As a close cousin of Hexagonal, Onion Architecture is certainly very powerful, but the extent to which we’ll apply its principles should be carefully considered.

For mid to larger scaled projects where multiple teams work, layering has very obvious advantages up its sleeves. 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. In my implementation, I intend to demonstrate some of the key layers of this architecture and how they work together. See example repository here.Note — The following is my interpretation of this Architecture Pattern and may not be as intended by it’s publishers. 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.

Onion Architecture: Going Beyond Layers

The circles symbolize distinct levels of responsibility. The deeper we go, the more we know about the domain and business rules. The outer rings are mechanisms (including different switchable modules), whereas the inside circles are fundamental domain logic. The outer layers rely on the inner layers, and the inner layers are unaffected by any changes being introduced in the outer rings. The domain entities are the heart and soul of the system. The onion architecture is based on a domain model with layers connected by interfaces.