Onion Architecture: A Guide to Clean and Sustainable Code

As long as only data is transferred the mapping process is tedious but manageable. As soon as the presentation layer would like to reuse business rules from the core domain model this approach’s drawbacks outweigh its benefits. 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).

This is why the architectural pattern is thought of as an onion. The DAL is essentially another section of the outer layer. In fact, I think of this not so much as the DAL layer and the presentation layer… Inside the infrastructure layer, you have your data access code, your presentation code and other code that communicates with the outside world.

Pros and Cons in Onion Architecture

Create a new class Entities/Product.cs in the Domain Project. Next, we will need to add the XML File (For Swagger Documentation). To do this, right-click the WebApi Project and go to properties. In the Build Tab enable the XML Documentation file and give an appropriate file name and location.

Business logic drives the application’s behavior and maintains data integrity. Domain entities and business logic are at the heart of Onion Architecture, promoting maintainability and scalability. If we put the traditional layered architecture in concentric circles we clearly see the application is built around data access and other infrastructure. Because the application has this coupling, when data access, web services, etc. change, the business logic layer will have to change. The world view difference is how to handle infrastructure.

Onion Architecture

In order to see how the application structures itself internally we need to drill down deeper. Surrounding this inner circle are layers of abstraction,
each one representing a different concern. One of the more popular ones is Clean Architecture, a design approach
that prioritizes maintainability, scalability, flexibility, and productivity. The path analysis showed that the three main factors influencing onion bulb production are plant height, bulb length, and bulb diameter.

Onion architecture also solves the problem that we confronted in three-tier architecture and N-Layer architecture. In Onion architecture, our layer communicates with each other using interfaces. The presentation layer handles user interface and interactions. Controllers receive user requests, orchestrate actions, and communicate with application services. View models represent the data and logic required for views. The presentation layer is responsible for user input validation and UI-related operations.

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Onion Architecture was introduced by Jeffrey Palermo to provide a better way to build applications in perspective of better testability, maintainability, and dependability. Onion Architecture addresses the challenges faced with 3-tier and n-tier architectures, and to provide a solution for common problems. Onion architecture layers interact to each other by using the Interfaces. C# programmers are drawn to Onion Architecture due to the dependency flows. If you are interested in learning more C# while working with the Onion Architecture, visit the TechRepublic Academy.

Testability is very high with the Onion architecture because everything depends on abstractions. The abstractions can be easily mocked with a mocking library such as Moq. To learn more about unit testing your projects in ASP.NET Core check out this article Testing MVC Controllers in ASP.NET Core. Let us take a look at what are the onion architecture software, and why we would want to implement it in our projects. This way, when you want to test it, you can just inject a mock that implements the interface your code is expecting to. So, the only place in your application that actually creates objects that are capable of doing IO is the application’s entrypoint.

Dependency Management

OnModelCreating method, we are configuring our database context based on the entity configurations from the same assembly. Before starting the sample API let us briefly review the Dapper. Independent of Database – You can swap out SQL Server or Oracle, for Mongo, Bigtable, CouchDB, or something else. Onion Architecture and Clean Architecture both are used to provide a standard architecture to the software. ONION ARCHITECTURE OVERVIEW

As shown in the above image, the Domain Model is the core and it consists of POCO entries.

• We can understand how this is being used in the application to follow DDD.
• Onion architecture consists of several concentric layers interacting with each other towards the core, which is the domain.
• This will have all the logic related to each Feature / Entity.
• 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 architecture pattern is heavily leaning on the infrastructure.

This layer is used to communicate with the presentation and repository layer. The service layer holds all the business logic of the entity. In this layer services interfaces are kept separate from their implementation for loose coupling and separation of concerns.

Performance Disadvantages of Clean Architecture: A Closer Look

Data access in Onion Architecture ensures separation of concerns and facilitates efficient data retrieval and storage. Domain entities represent core business concepts, encapsulating state and behavior. They remain persistent-ignorant and independent of infrastructure. The domain layer houses business logic, enforcing rules and validations.

Authentication, Response Wrappers, Error Logging and Job Processing is already covered in my other articles. Well the notion is Data access layer onion architecture technology keep changing after almost 3-4 years of life span. Like with many online examples, your example is missing real life examples. You can check my github repository for technical details. This library provides almost limitless opportunities for setting data validation rules. It is well compatible with CQRS due to pipeline behaviors.

Differences between Onion & Hexagonal Architecture​

This will be an Empty API Controller which will have API Versioning enabled in the Attribute and also a MediatR object. We will not have to re-define the API Versioning route or the Mediator object. Common pitfalls to avoid when implementing Onion Architecture include not separating concerns properly, creating tight coupling between layers, and not managing dependencies correctly. And finally, we saw how our Presentation layer is implemented as a separate project by decoupling the controllers from the main Web application.