Onion-based Software 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. The entities defined in the Domain layer are going to capture the information that is important for describing the problem domain. 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 flow of dependencies dictates what a certain layer in the Onion architecture can do. Because it depends on the layers below it in the hierarchy, it can only call the methods that are exposed by the lower layers. The main idea behind the Onion architecture is the flow of dependencies, or rather how the layers interact with each other.

Onion Architecture separates the application into layers based on their responsibilities. This separation makes the application more modular and easier to understand. Software architecture is an essential aspect of any software development project.

Peeling Back the Layers: Exploring Onion Architecture

So, when you need to test your infrastructure code, you can make a mock that implements the interface (libs like Python’s MagicMock and Go’s gomock are perfect for this). A Repository is a pattern for a collection of domain objects. The former are rules that are executed to implement a use case of your application. A Domain Service contains behavior that is not attached to a specific domain model. One of the core concepts in DDD is the Domain Model.A Domain Model is an entity that incorporates behavior and data from some business model. Onion Architecture is an architectural pattern which proposes that software should be made in layers, each layer with it’s own concern.

It’s responsible for dealing with the persistence (such as a database), and acts like a in-memory collection of domain objects. 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. This is when layers depend on each other to work appropriately. In our case, there should always be an inward dependency. This means that the code should only depend on what’s closer to the center, ignoring “outside” layers.

Cumbersome when you don’t have many business rules

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. Repositories, external APIs, Event listeners, and all other code that deal with IO in some way should be implemented in this layer. Your Domain models onion architecture can have Value objects in their attributes, but the opposite is not allowed. As this layer is purely logical, it should be pretty easy to test it, as you don’t have to worry about mocking IO operations. Each type of architecture has its advantages and disadvantages – that’s the whole point of why different versions are created.

• Just to make our solution a bit clean, let’s also add API Versioning to the WebAPI.
• Implementing Domain Driven Design (DDD) through onion architecture significantly improves code quality, lowers complexity, and enables the development of evolving business systems.
• It refers to the business knowledge that our software is trying to model.
• It’s responsible for dealing with the persistence (such as a database), and acts like a in-memory collection of domain objects.
• Any developer, familiar with the domain, should be able to understand the code, and easily know where to change things.Modifying the view layer should not break any domain logic.
• And the most challenging task was to find a balance between all these functions.

The Infrastructure Layer should not implement any business logic, as well as any use case flow. DTOs are well suited as objects with really specific formats and data. The application layer implements Application rules (sometimes called use cases) instead of Business rules. The Global Cloud Team specializes in different application architectures. We have over 450 specialists with various backgrounds so that we can assemble a team for any project. There are multiple interfaces, making it easy to get lost in the whole mix.

The Need to Follow an Architecture

It is particularly useful for complex applications that require flexibility and scalability. By following the principles of Onion Architecture, developers can create high-quality applications that meet the needs of their users and stakeholders. Onion Architecture requires a good understanding of software architecture principles and design patterns.

Onion Architecture uses the concept of layers, but they are different from 3-tier and n-tier architecture layers. Let’s see what each of these layers represents and should contain. This means that external changes won’t have any effect on the core. However, the slightest changes in the core will significantly influence all other layers. So, if you decide to apply some new features too late, you are likely to get into a lot of trouble. Onion architecture comes with very clear rules about priorities, dependence, and layers.

Infrastructure Layer

Figure 2 below outlines the domain within the application structure. Low coupling in which one module interacts with another module and does not need to be concerned with the other module’s internals. All the internal layers need not be concerned about internal implementation of external layers.

It represents the Web API or Unit Test project in a Web application. This layer implements the dependency injection principle, allowing the application to design a loosely linked structure and communicate with the internal layer using interfaces. Instead of building a highly decoupled structure, we often end up with several layers that are depending on each other. This is something really bad in building scalable applications and may pose issues with the growth of the codebase. To keep it clear, in the above diagram we can see that the presentation layer depends on the logics layer, which in turn depends on the data access and so on. Service Interface Layer – common operations like Add, Save, Delete should go in here within interfaces.

I’m going to show you a simple way of testing API contracts using Postman and Node.js. You can set this up very quickly.

Under this folder, add a new one and name it ProductFeatures. Now add a Product Class that inherits the Id from the BaseEntity. Create a new class Entities/Product.cs in the Domain Project. Next, we will need to add the XML File (For Swagger Documentation). To do this, right-click the WebApi Project and go to properties.

The application can be easily replaced or modified without affecting other layers thanks to the onion architecture. Future technology https://www.globalcloudteam.com/ and component integration will be made simpler as a result. The Onion Architecture relies heavily on the usage of interfaces.

C# Object oriented programming Composition vs Inheritance

This is also the layer that “knows” which operations should be performed atomically, thus the transaction-related code
is placed here. Note, however, that in the example above, the transactions field is actually an interface reference. We have now set our expectations for anyone wishing to charge a user for a transaction within our Application Services layer. However, we are not doing anything useful at the moment with the transaction so from this and following the layers of Onion Architecture we need to define our Domain Services layer.