**Course Title:** Mastering NestJS: Building Scalable Server-Side Applications **Section Title:** Working with Databases: TypeORM and Data Transfer Objects (DTOs) **Topic:** Integrating TypeORM with NestJS for database management In this topic, we will explore how to integrate TypeORM with NestJS to manage databases effectively. TypeORM is a popular ORM (Object-Relational Mapping) library for TypeScript that allows us to interact with databases using TypeScript classes. ### Why Use TypeORM with NestJS? TypeORM provides several benefits when used with NestJS, including: * **Type safety**: TypeORM uses TypeScript classes to define database entities, ensuring type safety and preventing runtime errors. * **Database portability**: TypeORM supports multiple databases, including MySQL, PostgreSQL, MongoDB, and more, making it easy to switch between databases. * **Lazy loading**: TypeORM supports lazy loading, which allows us to load related entities on demand, reducing the amount of data transferred between the database and the application. ### Installing TypeORM To install TypeORM, run the following command in your terminal: ```bash npm install --save @nestjs/typeorm typeorm ``` ### Configuring TypeORM To configure TypeORM, we need to create a `typeorm.config.ts` file in the root of our project. This file will contain the database connection settings and other configuration options. ```typescript // typeorm.config.ts import { TypeOrmModuleOptions } from '@nestjs/typeorm'; export const typeOrmConfig: TypeOrmModuleOptions = { type: 'postgres', host: 'localhost', port: 5432, username: 'username', password: 'password', database: 'database', entities: [__dirname + '/../**/*.entity{.ts,.js}'], synchronize: true, }; ``` ### Creating Database Entities To create database entities, we need to create TypeScript classes that extend the `Entity` class from TypeORM. Each entity class should have a `@Entity` decorator that specifies the name of the entity and the table it corresponds to. ```typescript // user.entity.ts import { Entity, Column, PrimaryGeneratedColumn } from 'typeorm'; @Entity() export class User { @PrimaryGeneratedColumn() id: number; @Column() name: string; @Column() email: string; } ``` ### Creating a TypeORM Module To use TypeORM in our NestJS application, we need to create a TypeORM module that imports the `TypeOrmModule` and configures it with our database connection settings. ```typescript // typeorm.module.ts import { Module } from '@nestjs/common'; import { TypeOrmModule } from '@nestjs/typeorm'; import { User } from './user.entity'; @Module({ imports: [ TypeOrmModule.forRoot({ ...typeOrmConfig, entities: [User], }), ], }) export class TypeOrmModule {} ``` ### Using TypeORM in Controllers To use TypeORM in our controllers, we need to inject the `Repository` class for the entity we want to interact with. ```typescript // user.controller.ts import { Controller, Get, InjectRepository } from '@nestjs/common'; import { Repository } from 'typeorm'; import { User } from './user.entity'; @Controller('users') export class UserController { constructor( @InjectRepository(User) private readonly userRepository: Repository<User>, ) {} @Get() async getUsers(): Promise<User[]> { return this.userRepository.find(); } } ``` ### Conclusion In this topic, we have covered how to integrate TypeORM with NestJS to manage databases effectively. We have created a TypeORM module, configured TypeORM, created database entities, and used TypeORM in our controllers. ### What's Next? In the next topic, we will cover how to create database entities and migrations using TypeORM. ### Leave a Comment or Ask for Help If you have any questions or need help with implementing TypeORM in your NestJS application, please leave a comment below. ### External Resources * [TypeORM Documentation](https://typeorm.io/) * [NestJS Documentation](https://docs.nestjs.com/)