How to Build Microservices with Onion Architecture: Hands-On Experience

Their knowledge was published in a book called Pattern-oriented Software Architecture – A System of Patterns. Next we will create Web Api controller for making HTTP Request for doing CRUD operations. Since this project will be calling the component of the “Application and Persistence” projects so make sure you add the project references to these 2 projects in your WebApi project. Note that we will be using this layer to perform Migrations and Generate our database. Presentation – it will hold the project for Presentation layer like web api, blazor, react angular.

Infra and UI are things that change with some regularity. So, it’s important to have an architecture in which you can swap the technology without mess up all around the application. To keep an application a long-life it’s important to have business logic and infrastructure service concerns independent from business logic. Now, let’s create a repository class to perform database operations on the entity, which implements IRepository. This repository contains a parameterized constructor with a parameter as Context, so when we create an instance of the repository, we pass a context so that the entity has the same context. The code snippet is mentioned below for the Repository class under OA.Repo project.

  • No conditions of the Internal layer with outer layers.
  • It creates a structure of layers, just like an onion, where you could test everything separately.
  • Here is a presenation by the author of the repository, using the above repository to explain clean architecture.
  • The actual type of database and the way of storing data is determined at the upper infrastructure level.
  • Concepts and technological details are important, but they are secondary.
  • However, all the other structures of the software are bound by its settings.

Add project reference for the Application project we build earlier. Change it’s target framework to .NET 5.0 which is the latest version right now. You can also add the Entity Framework Core package by running the command Install-Package Microsoft.EntityFrameworkCore on the Package Manager Console window of Visual Studio. Remember to select the Application project from the “Default project” dropdown. The Domain and Application layers are together known as Core layers of Onion Architecture.

Parallel in-between “DDD” and “IDesign method”

You can check my github repository for technical details. Hence, when you separate these requests, you can use different technologies for handler implementation . The main issues we faced were related to maintaining the low connectivity of microservices. That’s why it was difficult to immediately divide the functionality into the necessary microservices. Our customer needed a software system compatible with their hardware so that clients could buy equipment, install software and create and manage content.

Advantages of onion architecture

Inward moving, we encounter the Domain Services layer. In this layer is where the majority of our business logic lives, it carries out the operations to turn A into B, input into output, egg into chicken. It achieves this through interacting with the final layer, the Domain Model layer which is the representation of the high level data objects we use. It looks very similar to an onion with layers wrapping around a central core. Each of these layers represent a specific duty within the overall function of a service.

Application Layer in Onion Architecture

In that book they came to the conclusion that large systems need to be decomposed in order to keep structural sanity. The so-called Layer pattern should help to structure applications that can be decomposed into groups of subtasks in which each group of subtasks is at a particular level of abstraction. The initial inspiration came from the OSI 7-layer Model defined by the International Standardization Organization. N-layer, hexagonal and onion are all layered architecture styles, but each one features its own unique spin on distributed design and modular development.

Now, let’s develop the user interface for the User Listing, Add User, Edit User and Delete User. We create one more interface named IUserProfileService. This interface holds method signature which is accessed by the external layer for the UserProfile entity. The following code snippet is for the same (IUserProfileService.cs). This interface holds all methods signature which accesses by external layer for the User entity. The following code snippet is for the same (IUserService.cs).

Dependency Inversion Principle states that the high-level modules should not depend on low-level modules. We create interfaces in the Application Layer and these interfaces get implemented in the external Infrastructure Layer. This means that when writing our high-level business logic, we don’t want to depend directly on low-level stuff like databases, file systems, network connections, provider contracts, and such.

We’ve chosen MediatR to implement CQRS in the project. CQRS is a development principle claiming that a method must be either a command onion architecture that performs an action or a request that returns data. The system can be quickly tested because the application core is independent.

I try to be a guy that does not see everything in black and white. I like to learn, explore and understand but always taking into account the benefits of any new trend, principle or whatever. That’s the reason why I am not going to explain software architectures as a war, trying to convince you which one is the best and why you should use it alone. Using DIP, it is easily possible to switch the implementations. It is Architecture pattern which is introduced by Jeffrey Palermo in 2008, which will solve problems in maintaining application. In traditional architecture, where we use to implement by Database centeric architecture.

Ingredients of an Onion Architecture

In the same way the layers of Onion Architecture are separatable as they are loosely coupled, and this gives a highly testable architecture. You may think where the implementation of that Repository Interface may reside. Jeffrey Palermo mentioned that out on the edges we see UI, Infrastructure, and Tests. The outer layer is reserved for things that change often. These things should be intentionally isolated from the application core.

Advantages of onion architecture

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. The fundamental rule is that all code can depend on layers more central, but code cannot depend on layers further out from the core. This architecture is unashamedly biased toward object-oriented programming, and it puts objects before all others. Is Onion Architecture different than Clean Architecture?

Avoiding Repository pattern – implementing Onion Architecture with DbContext only

Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from its eventual run-time devices and databases. We can understand how this is being used in the application to follow DDD. This Domain Service is a process which is not the responsibility of the domain model itself and it is adding an operation to the model . In that CheckOut function , it is easy to see how this Application Service is being used to interact with external users and coordinate the use cases of our business rules . White app solution inclues all essential libraries with best practice, which will helps quick start project.

Developer can concentrate on Business requirement and build entities. It’s composed of domain concentric architecture where layers interface with each other towards the Domain (Entities/Classes). Some recommendations I’ve found suggests use of the DbContext directly in my Controllers, which I didn’t like. I don’t want my Controller code to get all messy with queries. I prefer them slim, and delegate the business processing and database operations to somebody else, like I currently do with the Service classes. Onion is the best in terms of separation and coupling problems.

Disadvantages of onion architecture

The Service layer holds interfaces with common operations, such as Add, Save, Edit, and Delete. Also, this layer is used to communicate between the UI layer and repository layer. The Service layer also could hold business logic for an entity.

Create your application now!

It’s possible to use an interface rather than the direct db context class, but I haven’t really dealt with projects where that became a necessity. I’m just trying to implement something that I can use with smaller applications, because clearly Repo/UoW approach is overkill for some scenarios and not to mention more code to write. It contains the Repository classes which implements the Repository interfaces. Contains the Service classes which implements the Service interfaces. Service classes are injected with Repository interfaces.

It holds POCO classes along with configuration classes. It represents the Domain Entities layer of the onion architecture. 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.

The presentation layer entry point is the LayerProductionPresenter. The LayerProductionPresenter uses the ILayerProductionApplicationService to open a factory and produces layers by using the previously opened factory. Because the application follows the strict layering pattern, the process layer has to translate domain objects into data transfer objects residing in the process layer .

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In order to get rid of this dependency we would need to introduce a small abstraction defined by the needs of the Core. We simply move all infrastructure and data access concerns to the external of the application and not into the center. Jeffrey Palermo proposed this approach called Onion Architecture on his blog 2008. However, Jeffrey liked to have an easy to remember name, which allows communicating the architecture pattern more effectively. Similar approaches have been mentioned in Ports & Adapters , Screaming Architecture (Robert C. Martin), DCI from James Coplien, and Trygve Reenskaug and BCE by Ivar Jacobson.

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