typescript 57 lines · 7 steps

Building a CRUD service in NestJS

A NestJS provider wraps a TypeORM repository to create, read, update, and delete users while guarding against duplicates and missing rows.

Explained by highlit
NestJS Intermediate crud dependency-injection repository-pattern error-handling orm
1import { Injectable, NotFoundException, ConflictException } from '@nestjs/common';
2import { InjectRepository } from '@nestjs/typeorm';
3import { Repository, DeepPartial } from 'typeorm';
4import { User } from './entities/user.entity';
5import { CreateUserDto } from './dto/create-user.dto';
6import { UpdateUserDto } from './dto/update-user.dto';
7 
8@Injectable()
9export class UsersService {
10 constructor(
11 @InjectRepository(User)
12 private readonly usersRepository: Repository<User>,
13 ) {}
14 
15 async create(dto: CreateUserDto): Promise<User> {
16 const existing = await this.usersRepository.findOne({
17 where: { email: dto.email },
18 });
19 
20 if (existing) {
21 throw new ConflictException(`Email ${dto.email} is already registered`);
22 }
23 
24 const user = this.usersRepository.create(dto as DeepPartial<User>);
25 return this.usersRepository.save(user);
26 }
27 
28 findAll(): Promise<User[]> {
29 return this.usersRepository.find({
30 order: { createdAt: 'DESC' },
31 });
32 }
33 
34 async findOne(id: string): Promise<User> {
35 const user = await this.usersRepository.findOne({ where: { id } });
36 
37 if (!user) {
38 throw new NotFoundException(`User ${id} not found`);
39 }
40 
41 return user;
42 }
43 
44 async update(id: string, dto: UpdateUserDto): Promise<User> {
45 const user = await this.findOne(id);
46 Object.assign(user, dto);
47 return this.usersRepository.save(user);
48 }
49 
50 async remove(id: string): Promise<void> {
51 const result = await this.usersRepository.delete(id);
52 
53 if (result.affected === 0) {
54 throw new NotFoundException(`User ${id} not found`);
55 }
56 }
57}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Injecting a repository keeps data access declarative and testable while the service focuses on business rules.
  2. 2Translating data conditions into NestJS HTTP exceptions gives callers meaningful status codes for free.
  3. 3Reusing findOne inside update centralizes the not-found check so every read path enforces the same guarantee.

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