Why Vertical Slice Architecture Beats Onion Architecture

07 Oct Why Vertical Slice Architecture Beats Onion Architecture

It doesn’t matter so long as the entities could be used by many different applications in the enterprise. Though these architectures all vary somewhat in their details, they are very similar. They all have the same objective, which is the separation of concerns. They all achieve this separation by dividing the software into layers. Each has at least one layer for business rules, and another for interfaces. The service layer is used to realize the communication between the storage layer and the project, at the same time, it can also save the business logic of the entity.

These architectural approaches are just variations of the same theme. In this article, we are going to learn about Onion architecture and what are its advantages. We will build a RESTful API that follows the Onion architecture, with ASP.NET Core and .NET 5.

Nothing in an inner circle can know anything at all about something in an outer circle. In particular, the name of something declared in an outer circle must not be mentioned by the code in the an inner circle. The repository might depend on a database client library, and is responsible for manipulating the data in the database/persistence layer.

Entities get populated by the repositories and those entities are injected into all the controllers and use cases that make use of them. Notice how all the red arrows move in one direction. Two classes, customer, are derived from baseentity. Moreover, it’s convenient to write from the back to the storage layer. There’s no need to worry about the actual interface. Also in this layer is any other adapter necessary to convert data from some external form, such as an external service, to the internal form used by the use cases and entities.

Great, we have seen how to implement the Presentation layer. 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. We have to realize that everything is a tradeoff in software engineering. We have prepared a project that follows the Onion architecture which we are going to use in the rest of the article. The Onion architecture is also commonly known as the “Clean architecture” or “Ports and adapters”.

How To Implement Components Of Ddd

Changes made in the code here do not affect/break the entities or external dependencies such as databases. Thinking of flexibility for elegant architectures, the domain layer is also where domain events could be triggered. Event Sourcing might be implemented here, with events being emitted when the domain entity changes.

• In particular, the name of something declared in an outer circle must not be mentioned by the code in the an inner circle.
• Conceptually, we can consider that the Infrastructure and Presentation layers are on the same level of the hierarchy.
• This repository implementation is also known as a secondary adapter in the Clean Architecture, since it implements an output port .
• To implement our domain layer, we start with a base abstract class called Entity, that other domain classes can extend.
• While the project used for this example is just an introduction point, you might feel comfortable enhancing it by introducing other concepts inside this architecture such as CQRS.

The third image is how we architect the communication among the classes and domains. Notice that data freely moves between packages and layers. Yet when you change the code in one package, it has no effect on the code in any of the other packages. We usually resolve this apparent contradiction by using the Dependency Inversion Principle. Similarly, data is converted, in this layer, from the form most convenient for entities and use cases, into the form most convenient for whatever persistence framework is being used.

The Dependency Rule

We do, however, expect that changes to the operation of the application will affect the use-cases and therefore the software in this layer. If the details of a use-case change, then some code in this layer will certainly be affected. The UI can change easily, without changing the rest of the system. A Web UI could be replaced with a console UI, for example, without changing the business rules. The business rules can be tested without the UI, Database, Web Server, or any other external element. In case you want to implement email feature logic, we define an IMailService in the Service Layer.

These exceptions will be handled by the higher layers of our architecture. We are going to use them in a global exception handler that will return the proper HTTP status code based on the type of exception that was thrown. All of the layers interact with each other strictly through the interfaces defined in the layers below. The flow of dependencies is towards the core of the Onion. We will explain why this is important in the next section. The repository we will create is going to implement the above interface storing data in the memory.

Often, the first exposure most people have to clean architecture is the main circular diagram explaining the high-level concepts of different architectural layers. The purpose of building these three directories is to place three layers of code. When coding later, you will see the relationship between the three layers. In addition, these three layers can be separated into three class libraries in practical application, which will be clearer.

Taking Care Of Database Migrations

If you’ve got this knowledge in place, you’ll find this style of architecture able to scale far past the traditional layered, “onion” architectures. In this diagram, the green arrows represent ‘input, and the red arrows represent output. Notice how the arrows in the first and third diagrams go in opposite directions.

This figure fully explains why it is called onion architecture. Around the second half of 2017, there will be relevant statements. However, a lot of articles are theoretical discussions, and we will use a project to complete this architecture today.

Let us take a look at what are the advantages of Onion architecture, and why we would want to implement it in our projects. The goal is to minimize coupling between slices and maximize coupling within a slice. Avi started as a Flash Animator in 1999, moving into programming as Action Script evolved.

Below features will be implemented in infrastructure layer. Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context. With our class that allows us to have a memory-based persistence layer created, we are now ready to use a mapper/repository approach. Mainly we will compose our domain methods here, and eventually, use what was injected from the infrastructure layer to persist data. This approach/architecture is really only appropriate for a minority of the typical requests in a system.

Presentation Layer

In our project, we have implemented almost all important libraries, you can plug & play (add/remove) based on your project requirement in StartUp.cs file. 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 could create an initialization script, connect to the Docker container while it is running the database server, and execute the script. But this is a lot of manual work, and it is error-prone. We have already prepared a working project for you and we’re going to be looking at each of the projects in the solution, and talking about how they fit into the Onion architecture.

The Clean Code Blog

But I believe it will help in many ways, especially to ensure maintainability and testability. Docker Compose to group our Web application container with a container running the PostgreSQL database image. That way, we won’t need to have PostgreSQL installed on our system. The purpose of the Presentation layer is to represent the entry point to our system so that consumers can interact with the data. We can implement this layer in many ways, for example creating a REST API, gRPC, etc.

In order to let you see clearly, I will create a directory entitymapper here and write a table structure mapping in the directory. It exists in the central part of the architecture and is composed of all business data entities. In the later practical code, I use ef to operate the database. Typically the data that crosses the boundaries is simple data structures. You can use basic structs or simple Data Transfer objects if you like. Or the data can simply be arguments in function calls.

Cqrs Pattern

Conforming to these simple rules is not hard, and will save you a lot of headaches going forward. By separating the software into layers, and conforming to The Dependency Rule, you will create a system that is intrinsically onion structure testable, with all the benefits that implies. When any of the external parts of the system become obsolete, like the database, or the web framework, you can replace those obsolete elements with a minimum of fuss.

Then, we explained how we can connect all of the layers using an ASP.NET Core Web API. ExceptionHandlingMiddleware with the dependency container, we would get a runtime exception, and we do not want that to happen. Great, we saw how we wired up all of the dependencies of our application. However, there are still a couple of things to take care of.

When formally doing a project, it’s best to write it in the configuration file. This layer is mainly used to operate the database. These three directories correspond to the three layers above. In this project, UI is actually the controller, which already exists. The most important part of this architecture is the code dependency principleFrom the outside in, and only in this direction. Code in the inner loop should not know anything about the outer loop。

However, I can’t think of any other way to do transaction management without the assistance of a framework and its middleware. It is helpful to separate a read-only model from a write-only model to implement the CQRS pattern. My day job is to develop apps for smartphones using Flutter.

What Data Crosses The Boundaries

In fact your business rules simply don’t know anything at all about the outside world. You can swap out Oracle or SQL Server, for Mongo, BigTable, CouchDB, or something else. Your business rules are not bound to the database. And finally, we saw how our Presentation layer is implemented as a separate https://globalcloudteam.com/ project by decoupling the controllers from the main Web application. Then we saw how the Service layer was created, where we are encapsulating our business logic. We started with the Domain layer, where we saw the definitions for our entities and repository interfaces and exceptions.

Step 1: Download Extension From Project Template

This is a last topic, Dependency Injection sounds like an exaggeration, but it essentially means assigning a class instance to a property of other classes. One of the reasons I like FastAPI is that it provides a DI mechanism by default. By splitting the Read model and Write model, we can flexibly respond to requests’ input and output. My dear seniors educated me about DRY for a long time, but I’ve come to realize that it’s not always absolute. Amazingly, by associating the Read model with the Response model and the Write model with the Request model, API documentation can be generated and validated. I’m trying to tell you that you are not using the repository pattern to replace RDBs in the future.

First, the constructor is private, which means trying to instantiate a cart with new Cart() would fail, and this is the expected behavior. As we are doing DDD, it is a nice practice to keep the domain class always in a valid state. Instead of directly instantiating an empty Cart object, we are using the Factory design pattern that returns an instance of the Cart class. Some validation could be made to ensure the creation is receiving all the required attributes. Similarly, we have getters and setters to provide all the interactions with the domain, and this is the reason why the class internal attributes/state is in a protected object .