- travel guide
The User Interface layer is responsible for presenting the information to the user and receiving input from the user. It can be a web application, a mobile application, or a desktop application. The User Interface layer depends on the Application layer and interacts with the user using the services and interfaces provided by the Application layer. Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context. In the Services.Abstractions project you can find the definitions for the service interfaces that are going to encapsulate the main business logic. Also, we are using the Contracts project to define the Data Transfer Objects (DTO) that we are going to consume with the service interfaces.
In 3-tier and n-tier architectures, none of the layers are independent; this fact raises a separation of concerns. The drawback of this traditional architecture is unnecessary coupling. The domain models and services will be inside this layer, containing all the business rules of the software. It should be purely logical, not performing any IO operations at all. According to traditional architecture, all the layers are interconnected and significantly dependent on one another.
This isolation is supported through the concept of ports and adapters. When doing software development, one of the most important things to have in mind is that your software should always be evolving. We should be able to build a software that can be maintained by future developers. The more involved approach is to define compilation modules representing the layers.
We are going to use them in a global exception handler that will return the proper HTTP status code based on the type of exception that was thrown. To demonstrate a common folder structure based on Onion Architecture, let’s consider a hypothetical e-commerce application. Developers can create unit tests that validate the functioning of each component by segmenting the program into tiny, independent components.
In fact, while there are numerous definitions of microservices, there is no single clear and unified definition. Broadly speaking, microservices are web services that create a type of service-oriented architecture. This layer will contain operation-specific orchestration and related logic for the application. This layer contains the implementation of the behaviour contracts defined in the Model layer.
Onion Architecture is suitable for most types of applications, but it is particularly useful for complex and long-lived applications that require a high level of maintainability and scalability. As a result, changing business needs can be accommodated more easily without having to completely rewrite the application’s software. The program can easily be expanded with additional features and capabilities because of its modular architecture without affecting the primary domain layer. This library provides almost limitless opportunities for setting data validation rules. Bounded context is a good fit for a microservices architecture. It is much easier to build a microservice around a bounded context.
It’s very powerful and closely connected to two other architectural styles—Layered and Hexagonal. Onion Architecture is more appealing for C# programmers than Java programmers. However, it’s up to the architect community to consider and argue in the discussion on whether or not to apply the architecture. The application’s entrypoint (usually, the main) should be responsible for instantiating all necessary dependencies and injecting them into your code.
Let’s understand different layers of the architecture and their responsibilities with an order creation use case. Application is divided into layers what is onion architecture where each layer has a set of responsibilities and addresses separate concerns. Each layer acts as modules/package/namespace within the application.
Additionally, domain objects are flat and free of cumbersome dependencies and code. Onion Architecture provides a robust and flexible approach to building modern web applications. By separating concerns into distinct layers and emphasizing dependency inversion, developers can create scalable, maintainable, and testable applications. I have covered the fundamental principles, implementation guidelines, best practices, and real-world example of Onion Architecture in ASP.NET Core in this blog.
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. It just contains data, and is used only in this use case as a return value. Then, you are implementing a use case which lets the user check her or his account balance. The code samples are taken from an example repository, which you can find
on GitHub. Java developers may not be as interested in Onion Architecture as C# developers.
The application is separated into layers, each with its own duties and concerns. Within the application, each layer functions as a module/package/namespace. But precisely what is Onion Architecture, on which principle it is based, what is the essence of Onion Architecture, when to implement it, etc., will be discussed in this article. Clean Architecture places a particular emphasis on using interfaces to decouple components, allowing components to be easily swapped out or replaced. For small to medium-sized applications or when the team is less experienced, the Onion Architecture is a sound choice, as it offers a good balance between complexity and maintainability.
Follow the repository pattern to encapsulate data access logic. Keep the domain layer independent of infrastructure-specific details. Data access in Onion Architecture ensures separation of concerns and facilitates efficient data retrieval and storage. To implement Onion Architecture, you need to separate the application into layers, where the core business logic is at the center and the infrastructure and implementation details are on the outer layers. You also need to ensure that each layer only depends on the layer beneath it, and use inversion of control and dependency injection to manage dependencies.
With its focus on separation of concerns and flexibility, Onion Architecture has become a go-to choice for building modern web applications. In this blog post, we will explore the fundamental concepts of Onion Architecture and delve into how it can be implemented using ASP.NET Core, accompanied by informative illustrations. In addition to promoting maintainability and testability, onion architecture also supports loose coupling and separation of concerns. This means that each layer of the application is independent of the other, making it easier to modify and extend the system without affecting other components.
Application Services interact with other services to fulfil the client’s request. Let’s consider the use case to create an order with a list of items. We first need to calculate the price including tax computation/discounts, etc., save order items and send order confirmation notification to the customer.
We define abstract interfaces at deeper layers and provide their concrete implementation at the outermost layer. This ensures we focus on the domain model without worrying too much about implementation details. We can also use dependency injection frameworks, like Spring, to connect interfaces with implementation at runtime.