Onion Architecture: Definition, Principles & Benefits

The very centre of the Model, this layer can have dependencies only on itself. It represents the Entities of the Business and the Behaviour of these Entities. Each layer bounds together concepts that will have a similar rate of change.

In the Startup/ConfigureServices of the API project, add these lines to register the Versioning. I have written a detailed article on API Versioning in ASP.NET Core 3.1 WebApi. Feel feel to read it to get a complete idea of this concept. As our ApplicationDbContext is configured, let’s generate the migrations and ultimately create a Database using Ef Core Tools – Code First Approach. And in the Startup class/ ConfigureServices method of the WebApi Just Add the following line. You can now see the advantage of this kind of approach.

Separation of concerns

Let’s say you have around 100 interfaces and 100 implementations. Do you add all these 100 lines of code to the Startup.cs to register them in the container? That would be insane from the maintainability point of view. To keep things clean, what we can do is, Create a DependencyInjection static Class for every layer of the solution and only add the corresponding.

In this article, we will cover the onion architecture using the ASP.Net 6 Web API. Onion architecture term is introduced by Jeffrey Palermo in 2008. Onion architecture solves common problems like coupling and separation of concerns.

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All layers must also supply information that inner layers can easily consume. The objective is to enhance coupling inside a vertical slice across layers while minimizing coupling across layers. The quick essence of that chapter is given in the Mark’s article. This article also nicely aligns layered, onion, and ports and adapters architectures, onion architecture so i recommend you to read it before proceeding with current article. Mark Seeman in the “Dependency Injection in .NET”, chapter 2, draw layers without something called “infrastructure”, effectively bypassing this piece of the software as well. He only focusing on analysis of data access as a crucial piece of infrastructure.

• The architecture does not depend on the data layer, as in a traditional three-tier architecture; it depends on real domain models.
• First, you need to add the Models folder that will be used to create the database entities.
• So, this article defines only the fact that every single external boundary is referencing and application instead of application referencing external boundaries.
• A Repository is a pattern for a collection of domain objects.
• 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.

You could go through that article which covers the same scenario. Remember we created an IApplicationDBContext Interface in the Application Layer? Create a new folder named Context and add a new class ApplicationDbContext. Create the repository class to perform the database operations which inherit the IRepository interface. Infrastructure Layer – persistence implementation, repository implementation, email and sms implementation, message queuing etc. Now in the ICustomServices folder, we will create the ICustomServices Interface, this interface holds the signature of the method.

Setting up the Controllers

The Service layer sits right above the Domain layer, which means that it has a reference to the Domain layer. The Service layer is split into two projects, Services.Abstractions and Services. Now, let’s https://www.globalcloudteam.com/ look at some of the custom exceptions that we have inside the Exceptions folder. Measure quality with metrics, generate diagrams and enforce decisions with code rules, right in Visual Studio.

Let’s see what each of these layers represents and should contain. This means that external changes won’t have any effect on the core. However, the slightest changes in the core will significantly influence all other layers. So, if you decide to apply some new features too late, you are likely to get into a lot of trouble. Let us have a closer look at the core of onion architecture, the way it works, and why it is so important. We have already discussed the separation of concerns as one of the principles in Onion Architecture, but we must understand the differences in couplings.

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So where do we keep the logic for implementing the interfaces in the domain service layer? Well, again, only if it doesn’t rely on infrastructure. In fact, many applications combine the two service layers into one. The layer is intended to act as an abstraction layer between an application’s Domain Entities layer and its Business Logic layer. We typically include APIs in this layer that offers object saving and retrieval functionality, usually by utilizing a database. A data access pattern encourages a more loosely coupled approach to data access.

We could create an initialization script, connect to the Docker container while it is running the database server, and execute the script. But this is a lot of manual work, and it is error-prone. To make it straightforward to download the application code and be able to run the application locally we are using Docker. With Docker we are wrapping our ASP.NET Core application inside of a Docker container. We are also using Docker Compose to group our Web application container with a container running the PostgreSQL database image. That way, we won’t need to have PostgreSQL installed on our system.

Benefits of an Onion Architecture

We create a generic repository that searches the source for data, maps the data from the source to a business entity, and tracks changes in the business entity back to the source. At deeper layers, we define abstract interfaces, while at the top layer, we give their concrete implementation. By doing this, we can keep our attention on the domain model and lessen our concern about implementation issues. We may also use dependency injection frameworks like Spring to link interfaces with implementation at runtime. For Example, Infrastructure layer implementations include external services used in Application Services and repositories used in the domain. The domain models and services will be inside this layer, containing all the business rules of the software.

Also, this layer is used to communicate between the UI layer and repository layer. The Service layer also could hold business logic for an entity. In this layer, service interfaces are kept separate from its implementation, keeping loose coupling and separation of concerns in mind. Let’s look at an example, The domain layer defines functionality that’s core to our sales order system. So perhaps one required function is calculating tax on an order.

What are the challenges with traditional architecture, and how onion architecture addressed them?

In order to access the Database, we introduce a Data Access Layer. This layer usually holds ORMs for ASP.NET to fetch/write to the database. When there is just a logical separation in your application, we can term it as layers or N Layers. 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.