A progressive Node.js framework for building efficient and scalable server-side applications.

• In this project, I simulated a coupling scenario using the Stable Dependencies Principle from the Clean Architecture book.
• The purpose of the project is to learn and demonstrate how this principle can be easily applied in NestJS.

The chapter "Component Coupling" introduces the Stable Dependencies Principle (SDP). It states that software components (modules in NestJS) should be designed so that dependencies flow in the direction of stability.

• What is a stable module in Clean Architecture?
  A stable module is a module that does not import code from many other places, but is heavily used by other components. It has high responsibility and should change rarely.

• What is a flexible module?
  A flexible module is one that imports code from many other components, but isn’t used by many. It has low responsibility and can be changed or replaced easily.

• How do they interact in this project?
  In this project, the stable component is forced to use code from the flexible component — creating an anti-pattern that should be avoided.

• Why are direct dependencies from stable to flexible modules problematic?
  If your stable component directly depends on a flexible one, changes in the flexible component can easily break the stable part of the system, which should ideally remain unaffected by such changes.

• How does Clean Architecture invert this dependency using interfaces?
  To fix this, we create an interface that defines a contract, and then use dependency injection to provide the flexible implementation. This inverts the dependency flow — the flexible module depends on the stable module's contract.

• Why are interfaces used between the stable and flexible components?
  Interfaces define a contract between the two components. This creates an artificial stability, making it clear when changes in the flexible module break the expected behavior.

• How does this reduce coupling and improve long-term stability?
  It makes developers aware that changes to the flexible class may break other parts of the code. As long as the interface is respected, the stable component stays safe and unaffected.

• In this case, the flexible module explicitly provides the implementation for the interface. Anywhere else in the project that uses this interface can import the flexible module, and NestJS will automatically inject the correct implementation using its DI container.

• What does this structure enable?
  It creates a more stable architecture since a clear contract ensures the stable component doesn't break when the implementation changes.

• What tradeoffs exist?
  The main tradeoff is that the "flexible" component becomes less flexible — it must now adhere to the interface contract, which limits certain types of changes or refactors.

• Clean Architecture by Robert C. Martin (Uncle Bob)
• NestJS documentation
• Any other sources you found useful

Nest framework TypeScript starter repository.

$ npm install

# development
$ npm run start

# watch mode
$ npm run start:dev

# production mode
$ npm run start:prod

# unit tests
$ npm run test

# e2e tests
$ npm run test:e2e

# test coverage
$ npm run test:cov

When you're ready to deploy your NestJS application to production, there are some key steps you can take to ensure it runs as efficiently as possible. Check out the deployment documentation for more information.

If you are looking for a cloud-based platform to deploy your NestJS application, check out Mau, our official platform for deploying NestJS applications on AWS. Mau makes deployment straightforward and fast, requiring just a few simple steps:

$ npm install -g @nestjs/mau
$ mau deploy

With Mau, you can deploy your application in just a few clicks, allowing you to focus on building features rather than managing infrastructure.

Check out a few resources that may come in handy when working with NestJS:

• Visit the NestJS Documentation to learn more about the framework.
• For questions and support, please visit our Discord channel.
• To dive deeper and get more hands-on experience, check out our official video courses.
• Deploy your application to AWS with the help of NestJS Mau in just a few clicks.
• Visualize your application graph and interact with the NestJS application in real-time using NestJS Devtools.
• Need help with your project (part-time to full-time)? Check out our official enterprise support.
• To stay in the loop and get updates, follow us on X and LinkedIn.
• Looking for a job, or have a job to offer? Check out our official Jobs board.

Nest is an MIT-licensed open source project. It can grow thanks to the sponsors and support by the amazing backers. If you'd like to join them, please read more here.

• Author - Kamil Myśliwiec
• Website - https://nestjs.com
• Twitter - @nestframework

Nest is MIT licensed.