no-hexagonal-architecture-violation.md

@sefr/no-hexagonal-architecture-violation

About the rule

Rule to check if Hexagonal architecture principles are respected. This rule doesn't require any additionnal configuration.

{
  // ...
  "plugins": ["@sefr"],
  "rules": {
    "@sefr/no-hexagonal-architecture-violation": "error"
  }
}

If you plan to use that rule, you must follow the following folders conventions :

Example :

Considering the following code organization :

src
├─── user-side
│    ├── some-primary-adapter.ts
│    └── some-other-controller.ts
├─── core
│    ├── some-primary-port.ts
│    ├── some-secondary-port.ts
│    ├── some-model.ts
│    ├── some-service.ts
│    └── some-other-model.ts
└─── server-side
     ├── some-http-client.secondary-adapter.ts
     └── some-data-access-object.ts

There a few synonyms you can use for core as business, business-logic, hexagon...

The root folder doesn't matter anyway.

✅ ESLint will not report an error for the following code :

/*
 Admit current file path is "src/user-side/some-primary-adapter.ts"
 */
import { SomePrimaryPort } from "../core/some-primary-port.ts";

export class SomePrimaryAdapter implements SomePrimaryPort {
	public doSomething(): void {
		// ...
    }
}

❌ ESLint will report an error for the following codes :

/*
 Admit current file path is "src/user-side/some-primary-adapter.ts"
 */
import { SomePrimaryPort } from "../server-side/some-http-client.secondary-adapter.ts";

export class SomePrimaryAdapter implements SomePrimaryPort {
	public doSomething(): void {
		// ...
	}
}

Previous code allows to bypass the core of the application which can break rules you want to apply.

/*
 Admit current file path is "src/core/some-primary-port.ts"
 */
import { SomeHttpClient } from "../server-side/some-http-client.secondary-adapter.ts";

const toto = new SomeHttpClient(/*...*/);

Previous code is violating the core principle of the hexagonal architecture by injecting technical logic among the business rules of the application.

Hexagonal architecture principle

This architecture is about isolating core-business logic from application or infrastructure purposes. However, this architecture does not show a clear way to structure your core-business layer.