Onion Architecture In Asp Net Core 6 Web Api

It’s highly recommended to use a multi-projects solution. This lack of organization at the project level leads to spaghetti code. To resolve this issue, we should design a multi-project solution, each layer should be a separate project. Onion architecture might seem hard in beginning but is widely accepted in the industry.

Similar to other architectural styles like Hexagonal, Layered, Clean Architecture, etc. it provides a solution for common problems. Domain Entities are the fundamental building block of Domain-Driven Design and they’re used to model concepts of your Ubiquitous Language in code. Entities are Domain concepts that have a unique identity in the problem domain. Domain entities encapsulate attributes and entity behaviour. It is supposed to be independent of specific technologies like databases or web APIs. Order is an entity and has attributes like OrderId, Address, UserInfo, OrderItems, PricingInfo and behaviour like AddOrderItems, GetPricingInfo, ValidateOrder, etc.

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. We are using a Web API built with ASP.NET Core to create a set of RESTful API endpoints for modifying the domain entities and allowing consumers to get back the data.

What Is The Onion Architecture?

Domain-Driven Design centres on the domain model that has a rich understanding of the processes and rules of a domain. onion architecture implements this concept and dramatically increases code quality, reduces complexity and enables evolutionary enterprise systems. Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context.

When you are creating a software that does not deal with business rules, this architecture won’t fit well. It would be really cumbersome to implement, for example, a simple gateway using Onion Architecture. It’s easier to maintain an application that has a good separation of concerns. You can change things in the Infrastructure Layer without having to worry about breaking a business rule.

onion architecture

But for most applications, it is usually easier to start with a simpler domain model, and only introduce complexity if it is required by the project. 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. We do not have to worry about how it will be implemented. The higher layers of the Onion will take care of implementing that interface transparently. It relies on dependency injection for doing it’s layer’s abstraction, so you can isolate your business rules from your infrastructure code, like repositories and views.

Leveraging Api Blueprint To Scale Application Development

However it’s principles can still be applied in a wider sense. Each layer bounds together concepts that will have a similar rate of change. Code should depend only on the same layer or layers more central to itself.

All outer reliance, similar to data set admittance and administration calls, are addressed in outside layers. Create the repository class to perform the database operations which inherit the IRepository interface. The onion architecture was embraced by the software industry and is a widely used architectural pattern, especially in enterprise software. Let’s understand different layers of the architecture and their responsibilities with an order creation use case. Low coupling in which one module interacts with another module and does not need to be concerned with the other module’s internals. All the internal layers need not be concerned about internal implementation of external layers.

I’m not sure if that’s an Onion Architecture already, it depends on your interpretation. On the other hand, we have the monoliths, which contain much more dependencies and services depend on one another on the code level. In this case, you’ll probably find much more outward dependencies to replace with interfaces. And there’s my framework dilemma, which I keep coming back to, mostly because of Uncle Bob’s writings that suggest that Onion and Hexagonal Architectures avoid framework dependencies. Hence, I’d say that to some extent all of us should take from Onion Architecture, but that extent should be decided on a case-by-case basis. In my implementation, I intend to demonstrate some of the key layers of this architecture and how they work together.

Implementation Of Onion Architecture

In Onion Architecture, the database is just a infrastructure detail. The rest of your code shouldn’t worry if you are storing your data in a database, in a file, or just in memory. A Repository is a pattern for a collection of domain objects. Repositories, external APIs, Event listeners, and all other code that deal with IO in some way should be implemented in this layer. The Infrastructure Layer should not implement any business logic, as well as any use case flow.

  • Each microservice has its own model, its own use cases and defines its own external interfaces for retrieving or modifying the data.
  • For eg – a front-end developer can work on presentation layers and backend developers can work on business layer and data access layers.
  • This layer contains the implementation of the behaviour contracts defined in the Model layer.
  • A Repository is a pattern for a collection of domain objects.
  • The goal is to minimize coupling between layers and maximize coupling within a vertical slice across layers.

Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects. It can be hard to implement a service using Onion Architecture when you have a database-centric background. By doing dependency injection in all the code, everything becomes easier to test.

With Layered And Hexagonal Architectures Understood, The Time Has Come To Talk About A Relative

I have followed his guidelines, however I need some verification on the structure of the project so far. Let’s create the table in SQL using the migration commands. Open the package manager console and switch the default project to Repositorylayer and execute the below commands one after another. Basically, it uses the concept of Layers but they are different from 3-tier and N-tier Layers. It provides better maintainability as all the code depends on deeper layers or the centre. We could create an initialization script, connect to the Docker container while it is running the database server, and execute the script.

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The big drawback to this top-down layered architecture is the coupling that it creates. Each layer is coupled to the layers below it, and each layer is often coupled to various infrastructure concerns. However, without coupling, our systems wouldn’t do anything useful, but this architecture 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.

The outer layers depend on inner layers and the inner layers are completely unaware of outer circles. Classes, methods, variables, and source code in general belonging to the outer circle depends on the inner circle but not vice versa. The outer layer is reserved for things that change often outside of the applications core business logic that interact with it. In the case of the UI, it is a service in itself, it will have its own logic and tests which validate it behaves as expected. If you are looking to test the entire system then that would be an end-to-end test that would be performed.

Pros And Cons In Onion Architecture

Application architecture is built on top of a domain model. To me, the essence of Onion Architecture is the application of Dependency Inversion Principle with architecturally defined priorities between layers. This is a simple use-case but the real question being asked is why. // DB interface sets out the operations allowed on our database.

onion architecture

In this article, we will cover the onion architecture using the ASP.Net 6 Web API. Onion architecture term is introduced by Jeffrey Palermo in 2008. Onion architecture solves common problems like coupling and separation of concerns. This layer lies in the center of the architecture where we have application entities which are the application model classes or database model classes.

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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. This layer is also allowed to know about everything contained in the inner layers, being able to import entities from the Application and Domain layers. It just contains data, and is used only in this use case as a return value. For example, let’s say you are developing a banking system. Then, you are implementing a use case which lets the user check her or his account balance.

Onion architecture layers interact to each other by using the Interfaces. C# programmers are drawn to Onion Architecture due to the dependency flows. If you are interested in learning more C# while working with the Onion Architecture, visit the TechRepublic Academy. 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.

Then, you need to implement the Transfer feature, which involves two Accounts. Domain-driven design is the concept that developers and domain experts should use the same names both in code and business domain. Showcasing how the Polysemy library can be used to implement a REST application conforming to the guidelines of the Clean Architecture model.

I find this pattern to help greatly with Test Driven Development . I often find it easier to drive out business logic code through tests than I do integrated code. Organising our application in layers https://globalcloudteam.com/ helps in achieving separation of concerns. It depends on the use cases and the complexity of the application. It is also possible to create more layers of abstractions depending on application needs.

The obvious advantage of the Onion architecture is that our controller’s methods become very thin. We moved all of the important business logic into the Service layer. Using dependency inversion throughout the project, depending on abstractions and not the implementations, allows us to switch out the implementation at runtime transparently. We are depending on abstractions at compile-time, which gives us strict contracts to work with, and we are being provided with the implementation at runtime. The Onion architecture is a form of layered architecture and we can visualize these layers as concentric circles.