Clean Architecture with GO

Introducing Clean architecture with Go.

Manato Kuroda

Nov 7, 2019·7 min read

Clean Architecture is designed to separate concerns by organizing code into several layers with a very explicit rule which enables us to create a testable and maintainable project. In this article, I’m going to highlight how Clean Architecture works in Go.

Example repo

You can view the full codebase at:

Updated:

• Add transactions support

Pre-requisites

The target of readers in this post is who:

• knows the basic idea of Clean Architecture
• wants to implement Go with Clean Architecture

So if you are not familiar with it, you can read some recommended articles to catch up.

• The Clean Code Blog
• Clean Architecture: Part 2 — The Clean Architecture
• Better Software Design with Clean Architecture

The darkness of software design

If you’ve been working as a programmer, you’ve probably run into the code that:

• is painful to add new features
• is too difficult to debug
• is hard or impossible to test without dependencies like a web server or database
• get a view and business logic mixed in widely, even can’t be separated
• is hard to understand what its purpose for
• has a lot of jobs only in one function and too long.

You might be even scared of committing a tiny little change because you don’t know how much it affects other functions and there are no unit tests, even if there is, it’s too complicated and mysterious, which means useless. Even if it is structured in MVC or MVVM, there are still issues around the project, of which business logic is leaking into controllers, the domain model is used across the entire project for different purposes and so on.

Advantages in Clean Architecture

Clean Architecture is one of the software designs of organizing the codebase and provides a solution to these issues you’ve ever seen. By introducing Clean Architecture you’ll get your code:

• highly decoupled from any UI, web framework or the database
• focusing more on business logic
• easily testable
• maintainable, visible and easier to understand

In Clean Architecture the codebase should be flexible and portable. It should not be dependent on any specific web framework or database, which means you could switch it to an entirely new platform. For instance, at the beginning of the project you use RDB but somehow even if you are forced to replace it with NoSQL for some reason, you can switch it without changing any business logic.

The only rules you need to know

When you implement Clean Architecture, you might try to follow the circle diagram completely, but actually, the author said:

Only Four Circles? No, the circles are schematic… There’s no rule that says you must always have just these four…

So you don’t need to implement it as it is, just takes it as an example for understanding the architecture. But there are important rules that you need to follow.

1. The dependencies can only point inward

In Clean Architecture the details like a web framework and databases are in the outer layers while important business rules are in the inner circles and have no knowledge of anything outside world. Following Acyclic Dependencies Principle(ADP), the dependencies only point inward in the circle, not point outward and no circulation.

2. Separation of details and abstracts

The details in Clean Architecture are the data, framework, database, and API. Using the details in the core layer means it violates The Dependency Rule. It should always be dependent on an abstract interface not specific knowledge of the details so it will be flexible and maintainable. As seen at the right of the diagram, it shows that Controller and Presenter are dependent on Use Case Input Port and Output Port which is defined as an interface, not specific logic(the details). But how is it possible to work without knowing the details in the outer layer?

The Dependency Inversion Principle (DIP) resolves this contradiction without violating the rules. If you are not sure about DIP, you can check out some articles before proceeding.

The Layers

We’ve learned a basic of the rule in Clean Architecture. Next, take a look at the layers before implementing them.

Entities

Entities is a domain model that has wide enterprise business rules and can be a set of data structures and functions.

ex.) A struct type of user, book and author.

Use Cases

Use cases contain application business rules using a domain model and have Input Port and Output Port.

Input Port is in charge of handling data from the outer layer and defined as abstract.

Output Port is in charge of handling data from Use cases to the outer layer and defined as abstract.

Interface Adapter

Interface Adapter handles the communication with the inner and the outer layer. It has only concerns about technological logic, not business logic.

Controllers are a set of a specific implementation of Input Port in Use Cases.

ex.) Convert form data before saving it in database

Presenter is a set of a specific implementation of Output Port in Use Cases.

ex.) Convert data from the database before passing to View

Frameworks and Drivers

Frameworks and drivers contain tools like databases, frameworks or API and basically do not have very much code.

ex.) API, database and web framework

Implementation of Clean Architecture in GO

Next, we’ll introduce Clean Architecture to Go and see how this works using a real use case. Let’s suppose that we’ll create a simple API responding to user data.

Now that we have the project structure as below:

.
├── domain
│   └── model
│       └── user.go
├── infrastructure
│   ├── datastore
│   │   └── db.go
│   └── router
│       └── router.go
├── interface
│   ├── controller
│   │   ├── app_controller.go
│   │   ├── context.go
│   │   └── user_controller.go
│   ├── presenter
│   │   └── user_presenter.go
│   └── repository
│       └── user_repository.go
├── main.go
├── registry
│   ├── registry.go
│   └── user_registry.go
├── usecase
│   ├── presenter
│   │   └── user_presenter.go
│   ├── repository
│   │   └── user_repository.go
│   └── interactor
│       └── user_interactor.go

Each directory has a role of each layer as following:

There’s no rule that you must always have just these four layers in Clean Architecture so actually, it depends on the teams or the projects.

Entities Layer

First off, we create a user domain model as Entities layer in domain/model/user.go :

Use Cases Layer

In Use cases layer we have three directories, repository, presenter and interactor . interactor is in charge of Input Port and presenter is in charge of Output Port. interactor has a set of methods of specific application business rules depending on repository and presenter interface.

Let’s create a findAll interface in usecase/repository/user_repository.go:

And a usecase/presenter/user_presenter.go :

Create a Get as a function of finding all users in usecase/interactor/user_interactor.go :

Interface Adapter Layer

In Interface Adapter layer, there are controllers , presenters and repository folders. controllers is in charge of the C of MVC model and handles API requests that come from the outer layer. repository is a specific implementation of repository in Use Cases and stores any database handler as Gateway.

Let’s create interface/controllers/user_controller.go :

In GetUsers it calls interactor in usecase and respond to user data.

And we add interface/controllers/app_controller.go :

That is a set of controllers defined to use in infrastructure/router/router.go later.

Next, create interface/presenters/user_presenter.go :

ResponseUsers handles user data before passing it to view basically but in this case, we add some text to the user name before responding to the client.

And add interface/repository/user_repository.go :

FindAll is an actual implementation of the interface in usecase/repository/user_repository.go that we’ve defined above and it’ll be injected as a method of handling database.

Frameworks and Drivers Layer

We have datastore and router in infrastructure. datastore is used as creating a database instance, in this case, we use gorm with MySQL. router is defined as a routing request using echo.

Let’s create datastore/db.go :

And router/router.go :

Registry

registry plays a role in resolving dependencies using constructor injection.

Let’s create registry/registry.go :

NewRegistry takes a db instance to pass down to interface/repository .

And add registry/user_registry.go :

NewUserController generates a controller with interactor. NewUserInteractor returns an interactor with a repository and presenter. NewUserRepository returns repository of interface passed with a database instance which fulfills usecase interface.

Booting

Now that we’re ready to boot a server with users endpoint. Let’s add some code to main.go :

We have echo framework for routing and pass it to router and controllers created by registry.NewRegistry .

Let’s try to see how it works at http://localhost:8080/users : (Make sure that there’s some record in your database)

It seems to work fine.

Conclusion

That’s it. We’ve created a very simple API responding to a user data with Clean Architecture. I like the idea of separating the different aspects of the product as highly decoupled layers.

I hope you will find the benefits I highlighted in this article.

You can view the final codebase at: