By controlling the domain through the API, and inserting all business logic within the domain, we have a portable application. Ubiquitous Language, which should be used in all forms of communication, from meetings and documentation all the way to source code, becoming the domain model implemented in the code. Domain Layer – It is the core of Onion architecture.

Layers do not necessarily need to be in different projects, especially in small applications. The answer is, as always, “it depends”, but I would argue the extra abstraction layer is definitely worth the effort for projects of sufficient size and scope. Also validation clutters the code of controllers, should be moved to a separate class (because of OOP+SRP which are the foundational principles behind CQRS). Adding a layer of abstraction for ORM or cloud provider are the best example of faux abstraction, the one that add no good but unnecessarily complicates the codebase.

Before closing my article – I’d like to leave you guys with one though – which is “loose coupling”. See the beauty of loose coupling achieved using this architecture. The advantages are not just limited to loose coupling but other features like Separation of concern and domain model approach makes it an awesome architecture to follow. Further, the biggest drawback of this architecture is unnecessary coupling that it creates.

Does Onion Architecture require a specific programming language or framework?​

Now i can see all my business logic concentrating on Services layer. No repositories injected in the MVC controller, only the services. Using contracts allows each layer to set its expectations onto the next and couples it to only what it requires to be. The Domain layer is where all the business rules belong.

It is not difficult when an application is small but in an enterprise-level application, it is too difficult to make the changes. The obvious advantage of the Onion architecture is that our controller’s methods become very thin. This is the true beauty of the Onion architecture. We moved all of the important business logic into the Service layer. There are more examples, but hopefully, you get the idea. We are hiding all the implementation details in the Infrastructure layer because it is at the top of the Onion architecture, while all of the lower layers depend on the interfaces .

It validates it, which could be a pure function, but it’s not domain logic that is valid. It depends on whether you are validating it in terms of domain concepts. First of all, I’d strongly advise that you read Evan’s DDD book. It’s really worth the investment and the time, because it is well written, it’s real-world approach for complex models, and its terminology is well accepted and precise. This is a simple use-case but the real question being asked is why.

Designing an Architecture

The Domain layer is responsible for maintaining the state and the behavior of the application. If an application is developed with the ORM entity framework then this layer holds POCO classes or Edmx with entities. These domain entities don’t have any dependencies. 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. It’s the outer-most layer, and keeps peripheral concerns like UI and tests.

The book Grokking Simplicity, I should tell you a little bit about it. It is all about introducing someone to functional programming. It’s all about how to make pure functions, how to extract out pure functions from existing code.

What is Onion Architecture?

The code snippet mentioned below is for the same action method for both GET and Post requests. We create a controller named UserController under the Controllers folder of the application. It has all ActionResult methods for the end-user interface of operations. We create both IUserService and IUserProfile interface instances; then we inject these in the controller’s constructor to get its object. The following is a partial code snippet for the UserController in which service interfaces are injected, using constructor dependency injection.

These days we have a different idea of what should go in a layer than 30 years ago, and we are more careful about where we put domain logic, presentation logic, and so on. But the architectural principles are all essentially the same. Yes, EFCore is installed in the Application layer as well. This approach is under the assumption that we would not switch away from EFCore for a very long time, which I think would not happen for at least the next years.

The services layer is another key component of the onion architecture. It sits between the domain and the infrastructure layers and provides an interface for the domain layer to interact with the infrastructure. The services layer contains the application’s business logic, where it coordinates the use of domain entities and defines the overall flow of the application.

• Because of the top to down coupling, you can peel layers off from the outside without ever effecting your inner layers of coding.
• In general, the deeper we dive, the closer we get to the domain and business rules.
• If an application is developed with the ORM entity framework then this layer holds POCO classes or Edmx with entities.
• He has a soft spot for all kinds of design, creative solutions, and philosophy.
• The main idea behind the Onion architecture is the flow of dependencies, or rather how the layers interact with each other.

These classes are used to create database tables. Notice, that the biggest file is the one for the infrastructure layer. The infrastructure has all the framework — in this case Spring Boot — database driver, and other dependencies, and itself depends on both domain and application.

Resource Center

None of the layer stand independent, which raises separation of concerns. One outer layer which may surprise many is Infrastructure. Is the database we use or an external dependency not part of our domain model layer? A very valid question so let’s explore it further.

Hello, I am a .Net architect working for a very very very wealthy company in the USA. My gut instinct is, they will understand and welcome this initiative. If so, they have so much money, it would not surprise me if they reach out to you to either hire you or contract you. It all depends on your application design and performance optimization. But you will surely end up having both EF and ADO.NET working side by side.

Next, let’s go to the Infrastructure Folder and add a layer for Database, . The presentation layer is where you would Ideally want to put the Project that the User can Access. To maintain structural Sanity in Mid to Larger Solutions, it is always recommended to follow some kind of architecture. You must have seen most of the Open Sourced Projects having multiple layers of Projects within a complex folder structure.

Why does Software Architecture matter?

The onion layer solves the problem of tight coupling that we faced with n-tier architecture. This architecture has Domain Layer, Repository Layer, Service Layer and Presentation Layer. Domain Layer will be at the core of the architecture. The Onion architecture was first introduced by Jeffrey Palermo, to overcome the issues of the traditional N-layered architecture approach which we discussed above.

Onion architecture

The GET request for the AddUser action method returns _AddUser partial view; the code snippet follows under the User folder of views. Now, we define the configuration for the UserProfile entity that will be used when the database table will be created by the entity. The code snippet is mentioned below for the UserProfile mapping entity (UserProfileMap.cs). The more involved approach is to define compilation modules representing the layers. Its disadvantage is a more complicated build structure and setup of your build tool of choice.

The main idea behind the Onion architecture is the flow of dependencies, or rather how the layers interact with each other. The deeper the layer resides inside the Onion, the fewer dependencies it has. At times, we had to move a particular functionality into a separate microservice if it appeared in many places in the system. On the contrary, if some functionalities were tightly connected, we had to combine microservices into one. And the most challenging task was to find a balance between all these functions.

Robert Martin introduced Clean Architecture in 2012. The core concepts are similar to onion architecture, but it has a slightly different terminology. Here, the domain model is referred to as an “entity”. Entity contains business-specific rules and logic, while the application operation specific logic sits in the use case.