Domain Driven Design and The Onion Architecture

Any developer, familiar with the domain, should be able to understand the code, and easily know where to change things.Modifying the view layer should not break any domain logic. Modifying the database modeling should not affect the software’s business rules. You should be able to easily test your domain logic.Then, we should start thinking about separating different concerns into different units of code. Onion architecture consists of several concentric layers interacting with each other towards the core, which is the domain. The architecture does not depend on the data layer, as in a traditional three-tier architecture; it depends on real domain models.

In this article, I will tell you about my experience of using onion architecture with a harmonized combination of DDD, ASP.NET Core Web API and CQRS for building microservices. Another significant advantage of onion architecture is its support for testing. With its clear separation of concerns, developers can easily test each layer of the application independently, ensuring that each component works as expected. This makes it easier to identify and fix issues in the codebase, reducing the risk of bugs and other errors that can impact the reliability and performance of the system. Onion architecture might seem hard in beginning but is widely accepted in the industry.

I’m going to show you a simple way of testing API contracts using Postman and Node.js. You can set this up very quickly.

Owner/developer City of San Diego and San Diego Theaters Inc.; project architect/designer, Kenn Lubin, Fine Art Imaging. The higher the coupling, the lower the ability to change and evolve the system. One of the foundational rules of the Onion Architecture is that dependencies can only ever point inward. That is, while it is fine for the UI to reference the Application Services, it would be absolute heresy for the Domain Model to reference its services.

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. Repositories used in the domain and external services used in Application Services are implemented at the infrastructure layer.

Dependency injection all the way! Easy to test

First, you need to create the Asp.net Core web API project using visual studio. After creating the project, we will add our layer to the project. After adding all the layers our project structure will look like this. Based on the DDD model, we’ve created onion architecture (aka hexagonal or clean architecture). To organize business logic for our project, we used Domain-Driven Design (DDD).

Onion Architecture requires additional code to implement the layers of the application. This can result in increased code overhead and a larger codebase, which can make the application more difficult to maintain. Onion Architecture adds additional layers to the application, which increases the complexity of the application. It may take longer to develop an application based on Onion Architecture compared to other architectural patterns. The clear separation of concerns between the layers makes it easier to modify and maintain the application.

Turn web pages into structured data

The Presentation layer, in the form of API controllers, interacts with the Core layer, promoting a clean and modular design. Is the database we use or an external dependency not part of our domain model layer? This layer lies in the center of the architecture where we have application entities which are the application model classes or database model classes.

The program can easily be expanded with additional features and capabilities because of its modular architecture without affecting the primary domain layer. It also exchanges data with the infrastructure layer in order to read and write data. Also, this layer offers an API that the infrastructure layer can leverage to obtain business needs, and it is in charge of turning those requirements into usable code. In this post, we’ll examine the main principles, advantages, and application of onion architecture to your projects. It’s responsible for dealing with the persistence (such as a database), and acts like a in-memory collection of domain objects. A Domain Service contains behavior that is not attached to a specific domain model.

Epstein Family Amphitheater, UC San Diego (Orchid for Public Architecture)

I will be implementing a CRUD (Create, Read, Update, Delete) operation in an ASP.NET Core Web API using the Onion Architecture and Prototype Design Pattern. Note that this example is simplified for demonstration purposes, and in a real-world scenario, you might want to add more features, error handling, validation, and security measures. This layer contains the implementation of the behaviour contracts defined in the Model layer.

The infrastructure layer can be changed out and new features added without impacting the rest of the application by keeping it independent from the other levels. The application layer stands between the domain layer and the infrastructure layer. Use cases, directives, and other elements make up the application logic, which executes the business logic of the application. In order to complete its functions, the application layer communicates with the domain layer.

practica onion architecture

Data access is typically implemented in the infrastructure layer. Use an ORM like Entity Framework Core for data access operations. Keep the domain layer independent of infrastructure-specific details. Data access in Onion Architecture ensures separation of concerns and onion architecture software facilitates efficient data retrieval and storage. In an application following the Onion Architecture, the business logic is typically stored in the Domain layer. It represents the core of the application and is independent of the infrastructure and the user interface.

The drawback of this traditional architecture is unnecessary coupling. The Infrastructure layer provides the implementation of the services and interfaces defined by the Domain layer. It is responsible for interacting with external systems, such as databases, messaging systems, and other services.

Use Interfaces and Contracts:

We will add the interfaces that consist of the data access pattern for reading and writing operations with the database. Domain services are responsible for holding domain logic and business rules. All the business logic should be implemented as a part of domain services. Domain services are orchestrated by application services to serve business use-case.

• The stadium becomes a cauldron of noise on matchdays when both sets of supporter’s exchange chants.
• The exception to this would be something like domain interfaces that contain infrastructure implementations.
• Domain-Driven Design centres on the domain model that has a rich understanding of the processes and rules of a domain.
• This design pattern facilitates the implementation of a flexible and reusable solution.
• This layer is used to communicate with the presentation and repository layer.
• A design competition was held in March of 2016 for the development of the site.