How to Build Microservices with Onion Architecture: Hands-On Experience

The Onion architecture was first introduced by Jeffrey Palermo, to overcome the issues of the traditional N-layered architecture approach. In this article, we are going to learn about Onion architecture and what are its advantages. We will build a RESTful API that follows the Onion architecture, with ASP.NET Core and .NET 5. Instead of each module being responsible of instantiating it’s own dependencies, it has its dependencies injected during it’s initialization. This way, when you want to test it, you can just inject a mock that implements the interface your code is expecting to.

onion architecture

Your Domain models can have Value objects in their attributes, but the opposite is not allowed. As this layer is purely logical, it should be pretty easy to test it, as you don’t have to worry about mocking IO operations. uses the concept of layers, but they are different from 3-tier and n-tier architecture layers. Let’s see what each of these layers represents and should contain. The fictional Frankenberg’s department store where Carol and Therese meet is actually two different former department stores.

C# versus C

With the CRUD logic out of the way, let’s set up EFCore in the Persistence Layer and try to generate a database. Install the following packages to the Persistence Project. Tip #2 – While running the application, you would see that it navigated to ../weatherforecast by default. In the WebApi Project, Properties drill down, you can find a launchsettings.json file. This file holds all the configurations required for the app launch. Thus, the swagger will open up by default every time you run the application.

onion architecture

It’s the outer-most layer, and keeps peripheral concerns like UI and tests. For a Web application, it represents the Web API or Unit Test project. This layer has an implementation of the dependency injection principle so that the application builds a loosely coupled structure and can communicate to the internal layer via interfaces. Onion Architecture solved these problem by defining layers from the core to the Infrastructure.

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It just contains data, and is used only in this use case as a return value. For example, let’s say you are developing a banking system. Then, you are implementing a use case which lets the user check her or his account balance. The domain layer is the innermost layer of the architecture. Several Cincinnati landmarks can be spotted in the 1988 Best Picture winner “Rain Man,” directed by Barry Levinson. Tom Cruise and Dustin Hoffman drive over the iconic John A. Roebling Suspension Bridge, completed in 1866, as they cross the Ohio River into Cincinnati.

onion architecture

It refers to the business knowledge that our software is trying to model. Domain-Driven Design centres on the domain model that has a rich understanding of the processes and rules of a domain. Onion architecture implements this concept and dramatically increases code quality, reduces complexity and enables evolutionary enterprise systems.

Flow of Dependencies

It helps easy adoption of new frameworks/technologies when old frameworks become obsolete. Similar to other architectural styles like Hexagonal, Layered, Clean Architecture, etc. it provides a solution for common problems. However, this architecture pattern is not a silver bullet to every problem. As with all software problems, we need to evaluate whether or not we need this additional abstraction as it is more suited for larger applications with many engineers working on them.

  • The former are rules that are executed to implement a use case of your application.
  • However, we are going to do something different from what you are normally used to when creating Web APIs.
  • We have to realize that everything is a tradeoff in software engineering.
  • Infrastructure services also referred to as Infrastructure adapters are the outermost layer in onion architecture.
  • We will also together build a WebApi that follows a variant of Onion Architecture so that we get to see why it is important to implement such an architecture in your upcoming projects.
  • This means the core layer is entirely decoupled from the outside world and can be tested independently of other components.

Outer layer data formats should not be used by inner layers. Data formats used in an API can vary from those used in a DB for persistence. Whenever data crosses layers/boundaries, it should be in a form that is convenient for that layer. API’s can have DTO’s, DB layer can have Entity Objects depending on how objects stored in a database vary from the domain model.

Data Folder

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.

Benefits of Onion Architecture

This is the final step of setting up Onion Architecture In ASP.NET Core. We will have to wire up a controller to the Application Layer. As our ApplicationDbContext is configured, let’s generate the migrations and ultimately create a Database using Ef Core Tools – Code First Approach.