**Course Title:** Mastering NestJS: Building Scalable Server-Side Applications **Section Title:** Dependency Injection and Service Providers **Topic:** Using custom providers for advanced use cases In this topic, we will explore the concept of custom providers in NestJS and how they can be used to handle advanced use cases. Custom providers are a powerful feature in NestJS that allow you to create and manage your own providers, which can be used to inject dependencies into your services and controllers. **What are Custom Providers?** Custom providers are a type of provider that you can create and manage yourself. They are similar to built-in providers, but you have full control over their implementation. Custom providers can be used to inject dependencies into your services and controllers, just like built-in providers. **Why Use Custom Providers?** There are several reasons why you might want to use custom providers: 1. **Complex Dependencies**: If you have complex dependencies that cannot be resolved by NestJS's built-in providers, you can create a custom provider to handle them. 2. **Custom Logic**: If you need to perform custom logic when injecting a dependency, you can create a custom provider to handle it. 3. **Advanced Use Cases**: Custom providers can be used to handle advanced use cases, such as caching, logging, or authentication. **Creating a Custom Provider** To create a custom provider, you need to create a class that implements the `Injectable` interface. This interface is a marker interface that indicates that a class can be used as a provider. Here is an example of a custom provider: ```typescript import { Injectable } from '@nestjs/common'; @Injectable() export class CustomProvider { private value: string; constructor() { this.value = 'Hello, World!'; } getValue(): string { return this.value; } } ``` **Using a Custom Provider** To use a custom provider, you need to add it to the providers array in your module. You can do this by importing the custom provider and adding it to the providers array: ```typescript import { Module } from '@nestjs/common'; import { CustomProvider } from './custom-provider'; @Module({ providers: [CustomProvider], }) export class AppModule {} ``` **Injecting a Custom Provider** To inject a custom provider into a service or controller, you can use the `@Inject` decorator: ```typescript import { Injectable } from '@nestjs/common'; import { CustomProvider } from './custom-provider'; @Injectable() export class MyService { constructor(private readonly customProvider: CustomProvider) {} doSomething(): string { return this.customProvider.getValue(); } } ``` **Conclusion** In this topic, we have explored the concept of custom providers in NestJS and how they can be used to handle advanced use cases. We have also seen how to create and use custom providers in our services and controllers. Custom providers are a powerful feature in NestJS that can be used to inject dependencies into our services and controllers. **What's Next?** In the next topic, we will explore how to integrate TypeORM with NestJS for database management. **Additional Resources** * [NestJS Documentation: Providers](https://docs.nestjs.com/fundamentals/providers) * [NestJS Documentation: Custom Providers](https://docs.nestjs.com/fundamentals/custom-providers) **Leave a Comment or Ask for Help** If you have any questions or need help with implementing custom providers in your NestJS application, please leave a comment below.