NestJS and TypeORM: A Powerful Duo for Building Robust Backends

Building a Robust Backend with NestJS and TypeORM

NestJS is a modern JavaScript web framework that enables developers to build efficient, scalable, and maintainable server-side applications. When combined with TypeORM, a powerful object-relational mapping (ORM) library, NestJS becomes an unbeatable duo for building robust backends. In this article, we’ll explore how to integrate TypeORM with NestJS and leverage the TypeORM QueryBuilder to perform complex database operations.

Prerequisites

Before diving into the tutorial, ensure you have:

• Node.js v12 LTS or Node >v14 installed on your computer
• Basic working knowledge of NestJS and JavaScript

Setting up NestJS

To get started, install NestJS using the CLI:
bash
npm install -g @nestjs/cli
nest new my-nestjs-app

This command scaffolds a basic NestJS application.

Configuring TypeORM

Install TypeORM and the SQLite driver:
bash
npm install typeorm sqlite3

In the src/app.module.ts file, import the TypeORM module and configure it to use SQLite:
“`typescript
import { Module } from ‘@nestjs/common’;
import { AppController } from ‘./app.controller’;
import { AppService } from ‘./app.service’;
import { TypeOrmModule } from ‘@nestjs/typeorm’;
import { Post } from ‘./post.entity’;

@Module({
imports: [
TypeOrmModule.forRoot({
type: ‘sqlite’,
database: ‘../db’,
entities: [Post],
synchronize: true,
}),
],
controllers: [AppController],
providers: [AppService],
})
export class AppModule {}
“`
Creating Database Entities

Create a post.entity.ts file to define the Post entity:
“`typescript
import { Entity, Column, PrimaryGeneratedColumn } from ‘typeorm’;

@Entity()
export class Post {
@PrimaryGeneratedColumn()
id: number;

@Column()
title: string;
}
“`
Using the TypeORM QueryBuilder

The TypeORM QueryBuilder provides a powerful way to perform complex database operations. Here’s an example of how to use it to retrieve all posts:
“`typescript
import { Injectable } from ‘@nestjs/common’;
import { InjectRepository } from ‘@nestjs/typeorm’;
import { Repository } from ‘typeorm’;
import { Post } from ‘./post.entity’;

@Injectable()
export class PostService {
constructor(
@InjectRepository(Post)
private readonly postRepository: Repository,
) {}

async getAllPosts(): PromisePerforming JOIN Operations

TypeORM provides several ways to perform JOIN operations. Here’s an example of how to use the QueryBuilder to perform a LEFT JOIN:
“`typescript
import { Injectable } from ‘@nestjs/common’;
import { InjectRepository } from ‘@nestjs/typeorm’;
import { Repository } from ‘typeorm’;
import { Post } from ‘./post.entity’;
import { Comment } from ‘./comment.entity’;

@Injectable()
export class PostService {
constructor(
@InjectRepository(Post)
private readonly postRepository: Repository,
) {}

async getPostComments(): Promise