The solution is moving the abstractions to the layer that uses it. This way, your DAL would reference/depend on the business layer so that it’s implementations implement the abstractions which exist in the business layer. Now, the business layer can literally exist in complete isolation as far as dependencies are concerned. This layer is used to communicate between the Repository layer and Main Project where it consists of exposable APIs. In this layer, the service interfaces are kept separate from their implementation for loose coupling and also the separation of concerns. Our fare calculation depends on external services such as routing information and fare models.

• Microservices and Domain-driven design are two different things but they come hand in hand while implementing microservices.
• Hence, when you separate these requests, you can use different technologies for handler implementation (Dapper, Entity Framework).
• I must set the context for the use of this architecture before proceeding.
• Do you remember how we split the Service layer into the Services.Abstractions and Services projects?

This architecture should be used when creating services that deal with business rules. 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. There are some cases where it’s hard to fit a behavior into a single domain model.Imagine that you are modeling a banking system, where you have the Account domain model. I’ll be writing more about the Onion Architecture as a default approach for building enterprise applications.

Domain Model

However, in the OnModelCreating method, we are configuring our database context based on the entity configurations from the same assembly. There are more examples, but hopefully, you get the idea. 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.

In both cases, you would have to create a new version of your DAL. But how would you account for these two different layers in your business layer? In layered architecture, the abstractions are in the DAL, so in order for the business layer to compile, it has to include a reference to the layer in which the abstractions exist.

Top Reasons for .NET Core’s Fast Adoption Rate

Its classes aren’t domain specific and are generic enough that they can be used in many different contexts. In a real world application you’d probably want the project to be part of a NuGet package that it can be used where needed. Consequently, the domain layer doesn’t have any dependencies on NuGet packages because it is used purely for business logic. It’s okay to use some NuGet packages in the core but it should be kept to the strict minimum. 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.

Onion architecture uses the concept of the layer but is different from N-layer architecture and 3-Tier architecture. In the Application layer, the FareRepository is able to retrieve data from external onion architecture sources and transform it into meaningful Business Entities. We will use the business domain of a Ride Sharing/Taxi Booking Application. It’s quite straight-forward, just think of Uber or Lyft.

Advantages of Onion Architecture in ASP.NET Core

This is how you can invert the dependencies to build scalable applications. The modular and decoupled architecture that the Onion Architecture encourages makes it simpler to maintain the application over time. Developers can make changes to one layer without impacting the other levels since each layer has a distinct function and communicates with other layers through clearly defined interfaces.

There are applications that might use a database as a storage service but only though some external infrastructure code that implements an interface which makes sense to the application core. Decoupling the application https://www.globalcloudteam.com/ from the database, file system, etc, lowers the cost of maintenance for the life of the application. The biggest offender (and most common) is the coupling of UI and business logic to data access.

Create and Configure Azure Network Watcher

This allows us to configure our services inside of the Startup class. Using dependency inversion throughout the project, depending on abstractions (interfaces) 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. In my implementation, I intend to demonstrate some of the key layers of this architecture and how they work together. See example repository here.Note — The following is my interpretation of this Architecture Pattern and may not be as intended by it’s publishers. Onion architecture might seem hard in beginning but is widely accepted in the industry.

Now, let’s look at some of the custom exceptions that we have inside the Exceptions folder. The Onion architecture is also commonly known as the “Clean architecture” or “Ports and adapters”. These architectural approaches are just variations of the same theme.

Value objects

That way, we won’t need to have PostgreSQL installed on our system. Now we only have one more layer left to complete our Onion architecture implementation. To learn how to implement the repository pattern with Entity Framework Core you can check out this article ASP.NET Core Web API – Repository Pattern. The entities defined in the Domain layer are going to capture the information that is important for describing the problem domain. Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects.

Based on the DDD model, we’ve created onion architecture (aka hexagonal or clean architecture). And finally, we saw how our Presentation layer is implemented as a separate project by decoupling the controllers from the main Web application. Then, we explained how we can connect all of the layers using an ASP.NET Core Web API. 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.

Project Structure.

We will implement these methods in the customs service code of the ICustomServices Interface given below. Now our service layer contains the reference of the repository layer. 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. First, you need to add the Models folder that will be used to create the database entities. In the Models folder, we will create the following database entities.