What Onion Has To Do With Clean Code?

This is where the “Onion Architecture” comes in. The term was first coined by Jeffery Palermo back in 2008 in a series of blog posts. It is intended to provide some insurance against the evolution of technology that can make products obsolete not long after they are developed (the technical term is “deprecated”). A classic example is Microsoft’s data access stack, which tends to change every few years (remember the demise of LINQ to SQL?).

What is onion architecture

Well, you are in luck 😛 I already have a complete implementation of Blazor Clean Architecture. In practical scenarios, you would actually want both EFCore and RAW SQL Queries for optimal performance. While ADO.NET is super fast, it’s very ideal for long queries with tons of joins. Whereas, EFCore comes with a lot features without compromising much on the performance.


But you will surely end up having both EF and ADO.NET working side by side. Your articles are well organized with deep details. I am salute your time and efforts to share articles. Onion / Hexagonal architecture is ideal for Monolith Applications. I have a full fledged Solution template that can get you started real easy. Yes, As a matter of fact I am already building a Solution for Clean Architecture in ASP.NET Core 3.1 WebApi.

What is onion architecture

It holds a generic repository class with its interface implementation. The Entity Framework Code First data access approach needs to create a data access context class that inherits from the DbContext class. This project represents the Repository layer of the onion architecture. Externalizing the database can be quite a change for some people used to thinking about applications as “database applications”. With Onion Architecture, there are no database applications.

In today’s world of request and response logic, you will need a repository interface and gateways to handle the situation. This facilitates by protecting your business from undesired dependencies. On the other hand, we can see dependencies and services relied upon each other on the code level. In such cases, you will find numerous dependencies to switch with interfaces. We create a controller named UserController under the Controllers folder of the application.

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Similar to the Application layer, we will have to create a new class just to register the dependencies and services of this layer to the service container. I have already written a detailed article on MediatR and CQRS patterns in ASP.NET Core 3.1 WebApi Project. You can follow that article and add the Required Commands and Handlers to the Application Layer.

This architecture doesn’t depend on the data layer, as in traditional multi-layer architectures, but rather on domain models. At the system’s core you will have your business logic, surrounding your core you can add your dependencies. Just like an onion, your levels are separate layers that do not intermingle, they are their own separate layers of coding. Because of the top to down https://globalcloudteam.com/ coupling, you can peel layers off from the outside without ever effecting your inner layers of coding. By forcing your coding to couple with only the layer under it, you are able to place key dependencies closer to the core to reduce downtime and increase system stability. When it comes to applying Onion Architecture, it is of utmost importance to understand when to implement it.

The whole application core is independent because it cannot reference any external libraries and therefore has no technology specific code. These interfaces should be focusing on the business meaning of that interface and not on the technical aspects. So the shape of the interface is directly related to the scenario it is used in the business logic.

According to him, the main deviation between Onion Architecture and Layered Architecture is the way of dependencies. Most people understand that in the layered architecture, almost all layers depend on the infrastructure layer. This results in bad coupling and changing the library or database provider could hamper overall business importance. Onion Architecture mainly aims at shielding your business fundamentals, and the dependency rule.

In the very center we see the Domain Model, which represents the state and behavior combination that models truth for the organization. Around the Domain Model are other layers with more behavior. The number of layers in the application core will vary, but remember that the Domain onion structure Model is the very center, and since all coupling is toward the center, the Domain Model is only coupled to itself. The first layer around the Domain Model is typically where we would find interfaces that provide object saving and retrieving behavior, called repository interfaces.

However, this module doesn’t depend on a database implementation. Infrastructure needs such as databases are always in the outermost layer of the onion, and so the module defines a Repository abstraction, which can load a Pool and persist events. Choices that could potentially be hard to reverse, such as which database technology to use, are moved to the outer layer where nothing depends on them, making those choices easier to revisit. The most important code goes in the middle, and depends only on very stable APIs such as the host language and one or two well tested and trusted libraries. The middle is where business rules are applied, and nothing else happens.

  • This makes the development easier, the testing of the application easier, the maintenance becomes easier.
  • As long as only data is transferred the mapping process is tedious but manageable.
  • The second layer of the onion contains the Application Interfaces.
  • The Infrastructure project in which we are working with database and database logics are part of the external layers.
  • We have refactored the application adhering to the onion architecture.
  • Domain model, domain services, and application services together make the application core.

The inner layer is the Domain Model and the outer one is the Infrastructure layer, which takes care of communicating with the external world. Based on the rules of the Onion Architecture, the SpeakerController could use UserSession directly since it’s in the same layer, but it cannot use ConferenceRepository directly. It must rely on something external passing in an instance of IConferenceRepository. This pattern is used throughout, and the IoC container makes this process seamless.

My Target Architecture

Then we saw how the Service layer was created, where we are encapsulating our business logic. We’ve shown you how to implement the Domain layer, Service layer, and Infrastructure layer. Also, we’ve shown you the Presentation layer implementation by decoupling the controllers from the main Web application.

What is onion architecture

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. The DbContext must have an instance of DbContextOptions in order to execute. We will use dependency injection, so we pass options via constructor dependency injection.

Onion Architecture Aka Clean Architecture

This layer is where you’re going to put your web server that converts a web request into either business rule, operation or a domain operation. It’s going to pierce through the layers and operate on the model. Accounting rules have been around for hundreds of years, but every business has different policies about how they deal with late fees and things like that.

Generate The Migrations And The Database

This means that each layer is coupled to the layers below it and often those layers end up being coupled to various infrastructure concerns. It is clear that coupling is necessary in order for an application to be able to do anything meaningful but this architecture pattern creates unnecessary coupling. As you can see in the picture, the three inner layers i.e. domain model, domain services, and application services are parts of the application core.

Is It Possible To Combine Differents Software Architectures?

We keep all domain objects that have business value in the core. Domain-Driven Design also has a service concept that is slightly different from the concept of an application service. 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.

It really helps me to understand and implement Onion Architecture. I have a request if you can include UoW pattern with NHibernate in this article with updated source code. Trackable Entities does include Unit of Work and has a nice implementation of the pattern.

To pass the data from UI to the controller to add a user, use the same view model named UserViewModel. The AuthorController has an action method named AddUser which returns the view to add a user. The code snippet mentioned below is for the same action method for both GET and Post requests. As the concept of dependency injection is central to the ASP.NET Core application, we register context, repository, and service to the dependency injection during the application start up. Thus, we register these as a Service in the ConfigureServices method in the StartUp class as per the following code snippet. Now, let’s create a repository class to perform database operations on the entity, which implements IRepository.

Onion architecture eliminates the dependance on layers that are developed before or after it. You can implement the repository interfaces however you wish, according to the needs of your application, but they would return and/or accept the POCO entities. You implement the interfaces in the Data project simply by adding repository classes and inserting code to interact with the object context. The sample project should show an example of doing this. We simply move all infrastructure and data access concerns to the external of the application and not into the center. Jeffrey Palermo proposed this approach called Onion Architecture on his blog 2008.

So this way, my business logic will end up at both the places ( i.e. repository as well as the controller) which again violates DRY( don’t repeat yourself). Another advantage this brings in is the testability – the services along with business logic can be tested independently without having an actual repository in place . So, we should stick to writing services which deal with encapsulating repositories calls as well as handle business logic. This way we define the purpose of each of the layer perfectly and in long run this architecture will be able to handle future maintenance elegantly. Infrastructure Layer– this is the outermost layer of onion architecture which deals with Infrastructure needs and provides the implementation of your repositories interfaces.

The degree of coupling you allow between layers all depends on your situation and constraints. You can, for example, have different entities for use internally within a service and entities returned by the service to consumers (DTO’s). Usually decoupling layers adds more development and maintenance costs, so it’s always a trade-off. The rule-of-thumb is, strive for loose coupling whenever possible, but weigh the costs and decouple as much as makes sense for your scenario.

Whenever dependency rules come in the picture, you have the leverage to implement the dependency inversion principle whenever an inner layer class wants to interact with outer layer class. Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context. Using this approach, we can encapsulate all of the rich business logic in the Domain and Service layers without ever having to know any implementation details. In the Service layer, we are going to depend only on the interfaces that are defined by the layer below, which is the Domain layer. We can write business logic without concern about any of the implementation details. If we need anything from an external system or service, we can just create an interface for it and consume it.

🙂 For a better example, check out my Trackable Entities samples, which include the use of dependency injection with repository and unit of work patterns. 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. So, like a typical onion, let’s work our way into the core and hopefully avoid any tears along the way.

We used Bootstrap, CSS, and JavaScript for the user interface design in this application. We create one more interface named IUserProfileService. This interface holds method signature which is accessed by the external layer for the UserProfile entity. The following code snippet is for the same (IUserProfileService.cs).

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