Onion Architecture DEV Community

A Web UI could be replaced with a console UI, for example, without changing the business rules. The term “Clean Architecture” is just the name of the article. The onion architecture is a specific application of the concepts explained in the article. Honestly, it’s not completely new, but I’m proposing it as a named, architectural pattern.

onion architecture

Such systems are very hard to understand and maintain. The drawback of this traditional architecture is unnecessary coupling. You will see the the Domain Model/Core layer is referenced across multiple layers, and that’s fine, to a certain degree. We are also able to write Unit Tests for our business logic whilst not coupling our tests to implementation either. Our fare calculation depends on external services such as routing information and fare models. Interfaces for these are defined in the Domain Services layer — IFareRepostory and IRouteService.

This pattern basically says that we can use a model for reading operations and another for writing operations.

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 https://www.globalcloudteam.com/. The Onion Architecture does not depend on any specific language or framework. You can implement it in basically any language that supports dependency injection. 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.

For this article, Let’s have a WebApi that has just one entity, Product. We will perform CRUD Operations on it while using the Onion architecture. In N Layer Architecture, the Database is usually the Core of the Entire Application, i.e It is the only layer that doesn’t have to depend on anything else.

Onion Architecture Is Interesting

Any developer, familiar with the domain, should be able to understand the code, and easily know where to change things. Onion Architecture layers are connected through interfaces. The home of the original Pilsner and the first Budweiser, the Czech Republic consumes more pivo per capita than anywhere else on earth, with more than 50 breweries operating in Prague today. The newest, Bohemia Goose, in New Town, serves Czech-style lagers and a full food menu focused on hearty duck and goose dishes, long part of the country’s culinary patrimony.

On the other hand, the service interfaces are public. The main idea behind the Onion architecture is the flow of dependencies, or rather how the layers interact with each other. The deeper the layer resides inside the Onion, the fewer dependencies it has. You can swap out Oracle or SQL Server, for Mongo, BigTable, CouchDB, or something else. The business rules can be tested without the UI, Database, Web Server, or any other external element. The UI can change easily, without changing the rest of the system.

Cumbersome when you don’t have many business rules

Yes, Infact you should use a Repository pattern always to keep a nice abstraction over the database. 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. There is no essential difference between n-tier, onion, hexagonal, layered etc architectures.

onion architecture

When doing software development, one of the most important things to have in mind is that your software should always be evolving. It will always be maintained, evolved, receiving new features, improvements, and bug fixes. No dependencies of the Internal layer with external layers. To submit a letter to the editor for publication, write to In the Application layer, the FareRepository is able to retrieve data from external sources and transform it into meaningful Business Entities. Note, I have chosen to call the most centre layer “Core” rather than Domain Models — a personal preference.

Why Onion Architecture?

Can be immediately tried in light of the fact that the application center doesn’t rely upon anything. Basically, it uses the concept of Layers but they are different from 3-tier and N-tier Layers. Photo by mayu ken on UnsplashClean Architecture, Hexagonal Architecture, and Onion architecture all circle around fundamentally the same concept, but with different language and nuances. We’ll take a look at what makes them similar and different. Formatting of the dates to user then remains totally unaffected by the decision made by the technical team working on the API.

  • The main problem with this architecture is that all layers are built on top of the Data Access Layer and are, in fact, tied to a certain type of data storage.
  • In practical scenarios, you would actually want both EFCore and RAW SQL Queries for optimal performance.
  • If you have a repository that expects a PostgreSQL client, the main should instantiate it and pass it to the repository during its initialization.
  • That’s quite everything in this simple yet powerful implementation of Onion Architecture in ASP.NET Core.
  • They are are horrible mistake made by Microsoft, and should never be used.

Instead, it may be driven by aesthetic feelings of the customer as well as by necessity to display dates in a timezone of user choice. Consider work with dates in regular JS SPA front-end. You may want to do adding/subtracting on dates, formatting the dates to human-readable form, formatting the onion software architecture dates to API-readable form, parsing the dates. Below is the list of criteria I use to move the functional to the CoreUtils project/folder. I would call the set of such patches to language as a CoreUtils. Might not be the best name ever, so feel free to suggest the better naming in comments.

Configuring Security Rules In Azure Firewall

We can implement this layer in many ways, for example creating a REST API, gRPC, etc. These are just some of the examples of what we could define in the Domain layer. We can be more or less strict, depending on our needs.

onion architecture

Being a Microsoft certified engineer, he specializes in web development and has experience in creating desktop and mobile solutions. Aliaksandr is fond of learning new technologies, conducting meetups and teaching newbies at internal company courses. After Adding the DbSet properties we need to add the migration using the package manager console and run the command Add-Migration. The external layer never depends on the external layer. There are other similar architectures that uses some of the same principles. This anti pattern has a lot of problems which are well described in Fowler’s article.

Domain Services

In addition, the onion architecture itself introduced certain problems. It took us some time to distribute functional parts between appropriate layers. But eventually, this problem was practically eliminated. 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. Add the Data in the domain that is used to add the database context class.

Leave a Reply

Your email address will not be published. Required fields are marked *