<a href="https://app.daily.dev/posts/part1-introduction-to-the-principles-of-clean-architecture-in-a-nodejs-api-express--44n1qpcxh" target="_blank" rel="noopener nofollow">Part 1 here</a>
<h3>Ports</h3>
These are simple interfaces linking the core and the infrastructure. They serve as a contract without any concrete implementation. You may find ports for technical dependencies, such as a logger, or for repositories (databases, etc.). An example of a User :
<pre><code class="language-ts">interface UserRepository {
 findByEmail(email: string): Promise&lt;User | null&gt;
 create(user: User): Promise&lt;void&gt;
}
</code></pre>
This contract includes two methods, each with input and output parameters. The code part therefore knows what it will receive from the infrastructure, and vice versa.
<h2>Technical details in “/infrastructure”</h2>
At the same level as core is the infrastructure folder, which manages all the technical details such as data persistence and calls to external services. This is where the interfaces defined in core are actually implemented.
<h3>The API</h3>
Let’s start with the API, the folder in which we’ll put Express’ config, controllers and other middleware.
In detail, for controllers, the “/infrastructure/api/controllers” folder groups controllers by resource or use case.
Their role here is to retrieve data from the HTTP request, validate and map it to the inputs expected by the use case, execute the use case and finally format the response. We’ll therefore find sub-folders for each resource, with a typescript file for the controller itself, the input and output DTOs, and the encoder/decoder for these inputs/outputs.
<h3>Adapters</h3>
As the name suggests, this directory contains the technical adapters for the ports defined on the core side. It’s very important to identify implementation dependencies in the tree structure. Let’s take our example of the User repository:
<pre><code class="language-ts">// /core/ports/user-repository.port.ts
interface UserRepository {
 findByEmail(email: string): Promise&lt;User | null&gt;
 save(user: User): Promise&lt;void&gt;
}

// /infrastructure/adapters/mongo/user.repository.ts
import { UserRepository } from &#x27;../../core/ports/user-repository.port.ts&#x27;
export class MongoUserRepository implements UserRepository {
 async findByEmail(email: string): Promise&lt;User | null&gt; {
 // logique d&#x27;accès MongoDB
 }
 async save(user: User): Promise&lt;void&gt; {
 // logique d&#x27;accès MongoDB
 }
}
</code></pre>
At tree level, we find “adapters/mongo”, which means that in this sub-directory we have all the technical implementation for accessing mongo DB. As you can see, the adapter takes over the contract specified in the port. If tomorrow I want to change my dependency to SQLite, for example, I’ll simply create a second adapter, change the dependency injection, and there’ll be no impact on the core.
Want to learn how implement it with typescript and express? See my udemy course! In <a href="https://www.udemy.com/course/clean-architecture-avec-typescript-et-express/?referralCode=8C9C5BF69F624247D63A" target="_blank" rel="noopener nofollow">french</a> or <a href="https://www.udemy.com/course/clean-architecture-with-typescript-and-nodejs-express/?referralCode=A0683A3DE7EDE1BD15A0" target="_blank" rel="noopener nofollow">english</a> 😉
Articles on Clean Architecture:
<ul>
<li><a href="https://dev.to/nlapointe/demystifying-clean-architecture-fundamentals-and-benefits-5ae7" target="_blank" rel="noopener nofollow">Demystifying Clean Architecture: Fundamentals and Benefits</a></li>
<li><a href="https://dev.to/nlapointe/clean-architecture-infrastructure-vs-core-492k" target="_blank" rel="noopener nofollow">Clean Architecture : Infrastructure vs Core</a></li>
<li><a href="https://dev.to/nlapointe/clean-architecture-business-rules-first-4dlo" target="_blank" rel="noopener nofollow">Clean Architecture: Business rules first!</a></li>
<li><a href="https://dev.to/nlapointe/introduction-to-the-principles-of-clean-architecture-in-a-nodejs-api-express-13e9" target="_blank" rel="noopener nofollow">Introduction to the principles of clean architecture in a NodeJs API (Express)</a></li>
</ul>

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Node.js developers

This post introduces the principles of clean architecture in a NodeJs API using Express. It explains the concept of ports, the purpose of the adapters directory, and the structure of the API folder.

[Part 2] Introduction to the principles of clean architecture in a NodeJs API (Express)