It is based on the concept of layers, each representing a distinct set of responsibilities. The architecture consists of an innermost core layer, surrounded by one or more layers of increasing abstraction. The innermost core layer contains the application’s most essential business logic and is isolated from the outside world.

• C# programmers are drawn to Onion Architecture due to the dependency flows.
• The Domain layer defines the entities, services, and interfaces that are required by the application.
• Overall, both Onion Architecture and Clean Architecture are powerful software design patterns that can be used to create modular, scalable, and maintainable software systems.
• This approach is an alternative to the traditional layered architecture.
• We started with the Domain layer, where we saw the definitions for our entities and repository interfaces and exceptions.
• Before we explore the promised benefits of layers and how they represent themselves in software architecture, we need to get rid of a common misconception regarding layers vs. tiers.

Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects. 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.

Onion Architecture in ASP.NET Core

It consists of algorithms that are essential to its purpose and implement the use cases that are the heart of the application. This Architecture style does have some learning curve for developers in the project, but once mastered, pays back many times. Finally, as with every solution in the IT industry, it is not a one-size-fits-all, and you should always consider if the architectural style matches your needs. The code samples are taken from an example repository, which you can find on GitHub.

From the technical perspective when we are dealing with files, sockets, HTTP requests, databases, etc we are working with streams of data. We want the hotel to serve us what we want, but not what they offer right?. The same thing is happening here, we want the DB to give the data the application needs but not the data it has. How can we architect an app that translates the sentence given by the user using a translation API?

Presentation Layer

The architecture does not depend on the data layer as in classic multi-tier architectures, but on the actual domain models. The main difference I’ve found in the implementations of Hexagonal Architecture and Onion Architecture lies mostly in the overall, more structured approach to the code layout of the latter. Making the concept a first-class citizen represented in the code guides implementation and gives more clear overall structure to the codebase. It’s composed of multiple concentric layers interfacing with each other towards the core. This architecture doesn’t depend on the data layer, as in traditional multi-layer architectures, but rather on domain models. The Onion.Factory sample is a very simple Domain Driven Design application which follows the onion architecture pattern.

The system can be quickly tested because the application core is independent. Dependency Injection is a necessary evil with this architecture. It causes us to rely heavily on something quite external that binds the entire application together and allows it to function at run-time. That being said, it’s not a big deal and it does not outweigh the pros. The higher the coupling, the lower the ability to change and evolve the system.

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

Using Gradle setup as an example, one can define three modules — domain, application, and infrastructure — in settings.gradle file. Then, in the build files corresponding to each of the modules, declare their dependencies, clearly defining the direction of dependencies. Additional complexity to the build setup and extra learning curve introduced by the layered approach pays back during development. It reduces the cognitive load on the programmer by giving a more concrete structural foundation and guidance.

Infrastructure abstraction makes it easier to adapt and adopt new technologies that best meet application requirements. To handle this, DDD requires that each language belongs to one application context. It defines a scope where a ubiquitous language can be used freely. Due to the ability to work on each layer independently, the separation of responsibilities makes it simpler to alter and maintain the code. These guidelines are crucial because they free developers from the burden of sifting through a maze of disorganized code in order to swiftly add new features and solve errors. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Dependency

This approach makes it possible to create a universal business logic that is not tied to anything. Automation — microservices should be deployed and updated automatically and independently from each other. Manual deployment and updating would be challenging because even the smallest project comprises from five to ten microservices, while large systems may comprise up to 500 microservices. The rider selects their destination, then are presented with an estimated price for their trip. Trip estimation is a business use-case, and it’s the one I’ve selected for our implementation. Figure 2 below outlines the domain within the application structure.

The core of the business logic should be free from any of the technical, and framework-related problems, allowing for easy testing and rapid development. Onion Architecture has great practical value, particularly for creating expansive, intricate software systems. It is simpler to test, maintain, and upgrade the codebase over time when an application is built in layers, which isolates the business logic from the display layer and infrastructure. The Application layer contains the application-specific logic. It is responsible for coordinating the interaction between the Domain layer, the Infrastructure layer, and the User Interface layer.

Catch “foreign” exception in adapter and convert them in own business exception is a good practice?

The Onion Architecture relies heavily on the Dependency Inversion principle. So tools like Guice, Ninject etc. are very helpful for those kinds of architectures but not a necessity. We can write business logic without concern about any of the implementation details.

Jeffrey Palermo introduced the concept of Onion Architecture in 2008. He wanted to develop a design approach for complex business applications by emphasizing the separation of concerns throughout the system. Onion Architecture is a software architecture pattern that follows the Dependency Inversion Principle. The architecture onion software architecture is named Onion Architecture because it has several layers around the core of the application, just like the layers of an onion. The core of the application contains the business logic and is independent of the infrastructure and the user interface. The infrastructure and user interface layers depend on the core layer.