Using Action Classes in NestJS for Better Code Separation and Reusability
Tags: webdev, programming, typescript, nestjs
Published: 2023-04-14 11:44:04

## Introduction:
NestJS is a popular Node.js framework for building scalable, maintainable web applications. One of the key features of NestJS is its ability to separate code into modules, controllers, and services, which can make your code more modular and easier to maintain.

However, as your application grows in complexity, you may find that your controllers become bloated with business logic that is not directly related to handling HTTP requests and responses. In this case, you can use action classes to further separate the code and improve reusability.

## What are Action Classes in NestJS?

Action classes are classes that encapsulate a specific business logic that can be executed independently of the controller. They can be used to perform a specific action, such as creating a new resource or updating an existing one.

By using action classes, you can separate the logic of creating a new resource from the controller itself, which can make your code more modular and easier to maintain. This is because the action class is responsible for executing a specific action, while the controller is responsible for handling the HTTP request and response.

## Advantages of Using Action Classes:

Using action classes provides several benefits over not using one:

1. **Separation of concerns**: By using an action class, you can separate the logic of creating a new resource from the controller, which can make your code more modular and easier to maintain.
2. **Reusability**: Since the action class is separate from the controller, it can be reused across different controllers or even across different applications.
3. **Testability**: By isolating the action logic in a separate class, it becomes easier to unit test that logic without having to worry about the HTTP request and response handling of the controller.
4. **Encapsulation**: The action class can encapsulate the details of the business logic, hiding it from the controller and making it more easily changeable without affecting the controller.

## How to Use Action Classes in NestJS:

To use action classes in NestJS, you can follow these steps:

1. Create an action class that encapsulates the specific business logic you want to perform.
2. Inject the action class into the controller using the NestJS dependency injection system.
3. Use the action class to perform the specific business logic in the controller.

Here's an example of using an action class to create a new resource (in this case, a post):

1. Create the `CreatePostAction` class in a separate file called `create-post.action.ts`.
2. Inject the `CreatePostAction` into a controller, such as the `PostsController`.
3. Use the execute method of the `CreatePostAction` to create a new post in the create endpoint of the controller.

> [_how to use action classes in nestjs_](https://dev.to/m4r14/how-to-use-action-classes-in-nestjs-djl)

## Conclusion:

Using action classes can make your code more modular, reusable, testable, and maintainable. By separating the business logic from the controller, you can make your code more easily changeable and less prone to errors. If you find yourself with bloated controllers, consider using action classes to further separate the code and improve reusability.

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