You must have seen most of the Open Sourced Projects having multiple layers of Projects within a complex folder structure. But here we need to add the project reference of the Domain layer in the repository layer. Write click on the project and then click the Add button after that we will add the project references in the Repository layer. We will follow the same project as we did for the Domain layer. Add the library project in your application and give a name to that project Repository layer.
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. That’s the exact vision I have while building this full-fledged Boilerplate template. And that’s why I included it inside my template because it can be useful for anyone. Also, I didn’t want to introduce CQRS and Event Sourcing with difficult examples with different databases and propagating changes from the Write DB to the Read DB.
Features Included
In general, the further in you go, the higher level the software becomes. But unfortunately, I must say that they are not for everyone. In some cases though, it might make more sense to use a Domain Interface to encapsulate business logic outside of the entity. The Supermarket.Core project has an Entities folder, which is the physical manifestation of the Domain Entities. At the core of the onion, you’ll find the Domain Layer, which is composed of Entities and Interfaces. Together they represent the core business logic of the application.
This architecture helps in achieving separation of concerns, testability, and maintainability by organizing the application into distinct layers. I am learning how to implement onion architecture using .Net core API. I understand that the focus of Onion architecture is more on flow of dependencies rather on how the layers interact with each other. But I found that domain entities are still accessible in the presentation layer (API layer). This is because the presentation layer has a project dependency on the application layer and the application layer depends on the domain layer where domain entities are defined as public. We cannot define it as internal because the entities will not be accessible by the application layer.
Layer Vs Tiers
As you can see, we mark the service implementations with the internal keyword, which means they will not be publicly available outside of the Services project. As we can see, it consists of the Web project, which is our ASP.NET Core application, and six class libraries. The Domain project will hold the Domain layer implementation.
Step 3: Select Onion Architecture project template
Onion architecture onion architecture .net core also solves the problem that we confronted in three-tier architecture and N-Layer architecture. In Onion architecture, our layer communicates with each other using interfaces. This allows us to easily switch out implementations or change data transfer formats without affecting the rest of the application. In this article, we have implemented the Onion architecture using the Entity Framework and Code First approach.
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Therefore what we do is that we create interfaces in the Application Layer and these interfaces get implemented in the external layers. This is also known as DIP or Dependency Inversion Principle. When there is just a logical separation in your application, we can term it as layers or N Layers. In cases where there is both a physical and logical separation of concerns, it is often referred to as n-tiered application where n is the number of separations. In this article, we will deal with Layered Architecture.
The domain layer, identical to the onion architecture layer, represents the core business rules and entities. However, we are going to do something different from what you are normally used to when creating Web APIs. By convention, the controllers are defined in the Controllers folder inside of the Web application.Why is this a problem? Because ASP.NET Core uses Dependency Injection everywhere, we need to have a reference to all of the projects in the solution from the Web application project.
- Basically, these 5 Classes would cover our CRUD Operations implementation.
- 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.
- Discussing the core forem open source software project — features, bugs, performance, self-hosting.
This allows us to easily switch out data access implementations or integrate with different external systems without affecting the rest of the application. This layer will define the DTOs and interfaces that our application services will implement. Like any architectural pattern, we are often trading off simplicity. So only use one of these patterns if we believe the application will grow with business needs and resources.
Structure of the template
For experienced teams that understand and can maintain the focus on layers but prefer more flexibility, the onion architecture may be a better choice. This is another variant that I have noticed in many huge solutions. Let’s say you have around 100 interfaces and 100 implementations. Do you add all these 100 lines of code to the Startup.cs to register them in the container? That would be insane from the maintainability point of view.
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- That’s a simple example of implementing a CRUD operation in an ASP.NET Core Web API using Onion Architecture.
- Notice that we create a switch expression around the exception instance and then perform a pattern matching based on the exception type.
- Although our applications have a different number of projects, the principles have remained the same.
- Feel feel to read it to get a complete idea of this concept.
- We can write business logic without concern about any of the implementation details.
The Contracts folder also includes the interfaces for the Infrastructure Layer. This lets the Domain Entities and Interfaces exploit the underlying Infrastructure of the application without knowing their implementation. Next, we’ll integrate the infrastructure layer to handle data access and implement repositories.
Now that we’ve integrated the Infrastructure layer, let’s expose our application’s functionality through an API in the Presentation layer. This layer will handle incoming requests and outgoing responses. We’ll also configure our dependencies and set up the connection string for our data access.