01 Dec Onion Architecture In ASP NET Core With CQRS Detailed

Business Logic is probably the most important part of this entire setup. It holds all the logic related to the Business requirements. Now, every application ideally has its own dedicated Database. In order to access the Database, we introduce a Data Access Layer. This layer usually holds ORMs for ASP.NET to fetch/write to the database. When there is just a logical separation in your application, we can term it as layers or N Layers.

The flow of dependencies is towards the core of the Onion. We will explain why this is important in the next section. When you are creating a software that does not deal with business rules, this architecture won’t fit well.

The application’s entrypoint — dependency injection

Modifying the database modeling should not affect the software’s business rules. Flexibility – the outer layer is completely decoupled from application logic making it easy to swap peripherals including databases, external services or testing tools. The Domain Model, Domain Services and Application Services layers make up the Application Core. The application core is the structure that should stay the same and contains all the logic to run the outer layer.

To summarize, Onion Architecture provides a well thought out approach to structuring software and is easy to visualize. While it doesn’t solve problems of interfaces interfering with the readability of code and changes to inner layers can surface breaking changes to dependent outer layers. Onion Architecture is simple to implement and enforces good relationships with one way coupling between software components. It should only return Domain Models without actually exposing the implementation of how this is done.

But we will just add the BaseAPI Controller as the base class. This layering can help in the separation of concerns, subdividing the solution into smaller units so that each unit is responsible for a specific task and also takes advantage of abstraction. For mid to larger scaled projects where multiple teams work, layering has very obvious advantages up its sleeves. It lets a specific team or individual work on a particular layer without disturbing the integrity of the others. It makes it much easier to track changes using source control.

Advantages of Onion Architecture

Aliaksandr is fond of learning new technologies, conducting meetups and teaching newbies at internal company courses. ASP.NET Core offers Health Checks Middleware and libraries for reporting the health of app infrastructure components. To put it simply, every action in Web API is either a request or a command , but it shouldn’t do both. Consequently, each API method is divided into requests and commands. For every service, we will write the CRUD operation using our generic repository.

This enforces true loose coupling between layers/components.The core application is built around an independent object model. All application core code can be compiled and run separate from infrastructure. The Onion Architecture is based on the ‘dependency inversion’ principle. The database is not the center of the universe anymore. With Onion Architecture, there are no database applications.

It’s paramount to understand the domain model of your business as this is basic input into your architecture. This domain modeling exercise is usually done jointly by architects and business stakeholders and usually produce domain model. This model is a non-technical model that describes the business you are in. This is also a communication vehicle between a technical person and a business person – all speaking the same language. This domain modeling eventually gives us a set of independently deployable components following domain-driven-design technique, which is a prerequisite of doing Microservices right. I am also not going to be touching on data integration challenges created by M&A as part of this article – I will tackle that head on in my next article.

Service Layer

Domain is where all business logic resides with classes and methods named using the ubiquitous language for the domain. Infrastructure is the outermost layer containing adapters for various technologies such as databases, user interface and external https://globalcloudteam.com/ services. In onion architecture, we have the domain layer, repository layer, service layer, and presentation layer. Onion architecture solves the problem that we face during the enterprise applications like coupling and separations of concerns.

• That’s why it was difficult to immediately divide the functionality into the necessary microservices.
• This layer communicates to both Web applications and repository projects.
• Interestingly, per your own admission, “EFCORE is already built on Repository pattern and UOW” and so why have IApplicationDbContext at all if all it does is expose EFCore classes and functions?
• 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.
• You can check my github repository for technical details.
• The application core is the structure that should stay the same and contains all the logic to run the outer layer.

Just some question in my mind,thought you can give clear answer on them,because i was working on CQRS but the project was microservice and is very big. Firstly, this is just a basic level implementation for the beginners. It just has a few less-than-ideal architecture choices (for long-lived solutions) that prevent me from recommending it as-is. You can move the composition logic in a separate project but in most cases it makes no difference, nor sense. Running migrations / seeding at startup might be a bit of performance bottleneck.

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. Most of the traditional architectures raise fundamental issues of tight coupling and separation of concerns. Onion Architecture was introduced by Jeffrey Palermo to provide a better way to build applications in perspective of better testability, maintainability, and dependability.

This layer acts as a middleware to provide data from Infrastructure to UI. Further, the biggest drawback of this architecture is unnecessary coupling that it creates. That’s all, I hope that you get a better picture of what the Onion architecture is and how its should be used. I feel that I must stress out that this architecture is only suitable for large robust projects which will be mantained for a long time.

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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. It is an ASP.NET Core Web application in this sample but it could be a Unit Test or Web API project. It is the most external part of an application by which the end-user can interact with the application. It builds loosely coupled applications with in-built dependency injection in ASP.NET Core. It holds POCO classes along with configuration classes.

I am going to talk about issues faced with traditional designs and then we will see how Onion Architecture addresses these common issues. The number of levels may differ, but the center is always the Domain Model, that is, those model classes that are used in the application and whose objects are stored in the database. Any solution needs extra modules which provide infrastructure helpers and tools. These modules should be attached externally to the Onion architecture and should not be dependant on anything else. I also find it very helpful to include a bootstrapper module which handles all the wiring and dependencies amongst the interfaces and their respective implementations.

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These objects have no behavior, being just bags of data used alongside your models. A Domain Service contains behavior that is not attached to a specific domain model. It could be basically a function, instead of a method. Imagine that you are modeling a banking system, where you have the Account domain model. Then, you need to implement the Transfer feature, which involves two Accounts.

This architecture pattern is not new, a variation of this pattern is called ports and adapters pattern, it’s sometimes called Hexagonal architecture as well. Whatever we call this architecture, its based upon plain old architecture principles – nothing earth shaking about any of them. My article below will also focus on three basic principles of software development that will enforce this architecture when it comes to its implementation. This application integration hell topic is also too broad but let’s find out if we can narrow it down. Even in the application layer, there is obviously no one approach to avoiding this this hell completely. Another approach to look at the problems described above is to look at the Traditional Architecture diagram below.

What are Some Problems with Onion Architecture?

We have now the knowledge of how the layer communicates with each other’s in onion architecture and how we can write the Generic code for the Interface repository and services. Now we can develop our project using onion architecture for API Development OR MVC Core Based projects. To pass the data from UI to a controller to edit a user, use same view model named UserViewModel. The UserController has an action method named EditUser, which returns the view to edit a user. It could be the web application, Web API, or Unit Test project.

Language and framework independent

Services.Abstractions project it will only be able to call methods that are exposed by this project. We are going to see why this is very useful later on when we get to the Presentation layer. We have prepared a project that follows the Onion architecture which we are going to use in the rest of the article.

Also, the code is easier to test due to dependency injection, which also contributes to making the software more maintainable. Example main()So, the only place in your application that actually creates objects that are capable of doing IO is the application’s entrypoint. The Infrastructure Layer uses them, but is onion structure does not create them. 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. It’s responsible for dealing with the persistence , and acts like a in-memory collection of domain objects.

Onion architecture consists of several concentric layers interacting with each other towards the core, which is the domain. The architecture does not depend on the data layer, as in a traditional three-tier architecture; it depends on real domain models. In this article, we have implemented the Onion architecture using the Entity Framework and Code First approach.

At the center of Onion Architecture is the domain model, which represents the business and behavior objects. Around the domain layer are other layers, with more behaviors. As per traditional architecture, the UI layer interacts to business logic, and business logic talks to the data layer, and all the layers are mixed up and depend heavily on each other.