**Course Title:** Mastering NestJS: Building Scalable Server-Side Applications **Section Title:** Dependency Injection and Service Providers **Topic:** Creating and using services for business logic In this topic, we will explore how to create and use services for business logic in a NestJS application. Services are a crucial part of any application, as they encapsulate complex business logic and make it reusable throughout the application. ### What are Services in NestJS? In NestJS, a service is a class that provides a specific functionality or business logic. Services are typically used to perform complex operations, such as data access, calculations, or external API calls. They are designed to be reusable and can be injected into other parts of the application, such as controllers or other services. ### Creating a Service To create a service in NestJS, you can use the `@Injectable()` decorator, which indicates to the NestJS framework that this class should be instantiated and managed by the dependency injection system. ```typescript // src/app/services/example.service.ts import { Injectable } from '@nestjs/common'; @Injectable() export class ExampleService { private readonly logger = new Logger(ExampleService.name); constructor() { this.logger.log('ExampleService initialized'); } public doSomething(): string { return 'Something was done'; } } ``` In this example, we have created a simple service called `ExampleService`. The service has a constructor that logs a message to the console, and a method called `doSomething()` that returns a string. ### Using a Service in a Controller To use a service in a controller, you can inject it using the `@Inject()` decorator. ```typescript // src/app/controllers/example.controller.ts import { Controller, Get, Inject } from '@nestjs/common'; import { ExampleService } from './example.service'; @Controller('example') export class ExampleController { constructor(private readonly exampleService: ExampleService) {} @Get() public getExample(): string { return this.exampleService.doSomething(); } } ``` In this example, we have created a controller called `ExampleController`. The controller has a constructor that injects an instance of the `ExampleService`, and a method called `getExample()` that calls the `doSomething()` method of the service. ### Best Practices When creating services, keep the following best practices in mind: * Keep services focused on a specific business logic or functionality. * Use services to encapsulate complex operations or data access. * Use dependency injection to manage services and make them reusable. * Avoid using services for simple operations or calculations. ### Conclusion In this topic, we have explored how to create and use services for business logic in a NestJS application. Services are a crucial part of any application, as they encapsulate complex business logic and make it reusable throughout the application. By following best practices and using dependency injection, you can create robust and maintainable services that make your application scalable and scalable. **Additional Resources:** * [NestJS Documentation: Services](https://docs.nestjs.com/fundamentals/services) * [NestJS Documentation: Dependency Injection](https://docs.nestjs.com/fundamentals/injection) **Leave a comment or ask for help if you have any questions or need further clarification on this topic.**