Peeling Back the Layers: Exploring Onion Architecture Knoldus Blogs

This means that each layer is coupled to the layers below it and often those layers end up being coupled to various infrastructure concerns. It is clear that coupling is necessary in order for an application to be able to do anything meaningful but this architecture pattern creates unnecessary coupling. Most of the traditional architectures raise fundamental issues of tight coupling and separation of concerns. Onion Architecture was introduced by Jeffrey Palermo to provide a better way to build applications in perspective of better testability, maintainability, and dependability.

In particular, the name of something declared in an outer circle must not be mentioned by the code in the an inner circle. That includes, functions, classes, variables, or any other named software entity. As with any pattern, there are benefits and drawbacks to using hexagonal architecture. These eight steps show how to structure the Lambda function code using a hexagonal architecture.

Layers of Onion architecture

Jeffrey Palermo mentioned that out on the edges we see UI, Infrastructure, and Tests. These things should be intentionally isolated from the application core. The pattern can help improve code testability because of the encapsulation and separation of concerns provided. This approach can also be used with compute solutions other than Lambda, which may be useful in code migration projects.

Each of these layers represent a specific duty within the overall function of a service. Now, let’s work on the Core Layers starting from the Domain Project. It basically has the models/entities, Exception, validation rules, Settings, and anything that is quite common throughout the solution. 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. In software development, architecture plays a critical role in determining the quality, scalability, and maintainability of a software system.

Development

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). I am planning to build a fully-fledged Clean what is onion architecture Architecture Solution Template, which you guys can just download and start using for your new projects in no time. That’s quite everything in this simple yet powerful implementation of Onion Architecture in ASP.NET Core.

The controller is developed to handle operations requests for both User and UserProfile entities. Now, let’s develop the user interface for the User Listing, Add User, Edit User and Delete User. The layer higher in the hierarchy (Layer N+ 1) only uses services of a layer N. No further, direct dependencies are allowed between layers.

Key Layers of Onion Architecture:

This is also known as DIP or Dependency Inversion Principle. Let’s look at one of the most popular Architecture in ASP.NET Core Applications. Here is a simple diagrammatic representation of a variation of the N-Layer Architecture. The presentation Layer usually holds the Part that the User can interact with, i.e, WebApi, MVC, Webforms, and so on. Business Logic is probably the most important part of this entire setup. It holds all the logic related to the Business requirements.

• DTOs are well suited as objects with really specific formats and data.
• And since the core layer shouldn’t be changed very often (ideally shouldn’t be changed at all) it helps you to pay attention to it during code-reviews.
• Still, most people can enjoy onions in their cooking with minimal or no issues.
• Domain and Application Layer will be at the center of the design.
• It just contains data, and is used only in this use case as a return value.

The inner layers shouldn’t know if your application is being exposed through an API, through a CLI, or whatever. The parts of your code that expose your application to the outside world are also part of the Infrastructure Layer, as they deal with IO. Usually, each domain aggregate has its own repository (if it should be persisted), so you could have a repository for Accounts, another for Customers, and so on. It just contains data, and is used only in this use case as a return value.

Dependency Injection:

For eg – a front-end developer can work on presentation layers and back-end developers can work on business layer and data access layers. Onion Architecture and Clean Architecture both are used to provide a standard architecture to the software. These architectures play a key role when we build large and complex projects which require regular enhancements.In this article, we will know about Onion architecture and Clean architecture in detail. Also, we will see a basic example of .Net Core-based application to understand onion and clean architecture.Before we proceed, we should understand what was the concern with prior architecture i.e. The Onion Architecture relies heavily on the Dependency Inversion principle.

The main premise of this architecture is that it controls coupling. However, you could also check the code on my GitHub to get a detailed understanding. However, I have covered a few of these topics in other articles in my blog already. You could go through them to understand the core concepts and to learn how everything works.

What are the common pitfalls to avoid when implementing Onion Architecture?​

To illustrate the layer architecture, we will analyze a Layer.Factory code sample that is available on github [13]. The Layer.Factory sample is a very simple Domain Driven Design sample application which follows the layered architecture pattern. The idea is that the domain model behind it represents a factory which produces layers (what a coincidence). In order to be able to create layers a factory responsible for creating layers must be created first. In order to analyze our sample application, we use a tool called Structure101 Studio. Structure101 Studio is a commercial tool which helps to visualize and organize large code bases in various programming languages.

Being a Microsoft certified engineer, he specializes in web development and has experience in creating desktop and mobile solutions. Aliaksandr is fond of learning new technologies, conducting meetups and teaching newbies at internal company courses. Let’s see what each of these layers represents and what should each contain.

The Onion Architecture 🧅

Hope this article helps you in a clear understanding of Onion Architecture. Let’s run and test this application to check the output in swagger or postman. This contains the Core Business Logic as part of our project which acts as a layer between the Repositorylayer and Controller. Basically, it uses the concept of Layers but they are different from 3-tier and N-tier Layers. I am Computer Science Engineer, with an interest in AI and have worked on research projects in startups.