NestJS TypeORM

Installing and Configuring TypeORM

@nestjs/typeorm wraps TypeORM so entities and repositories participate in Nest's DI container. You configure a root connection once, then import feature repositories where needed.

import { TypeOrmModule } from '@nestjs/typeorm';

TypeOrmModule.forRoot({
  type: 'postgres',
  host: 'localhost',
  port: 5432,
  username: 'nest',
  password: 'secret',
  database: 'nest',
  autoLoadEntities: true,
  synchronize: false,
})

autoLoadEntities: true registers entities from feature modules automatically. Keep synchronize: false in production and use migrations instead.

Entity and Repository Usage

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

  @Column({ unique: true })
  email: string;
}

@Injectable()
export class UsersService {
  constructor(
    @InjectRepository(User)
    private readonly usersRepo: Repository<User>,
  ) {}

  findAll() {
    return this.usersRepo.find();
  }
}

• @Entity() maps a class to a database table.
• @InjectRepository(Entity) injects TypeORM's Repository<T> for that entity.
• TypeOrmModule.forFeature([User]) must be imported in the feature module.
• Repository methods like find, findOneBy, save, and delete cover most CRUD cases.

TypeORM Nest Cheatsheet

Core TypeORM patterns inside Nest modules.

Defining Relations

TypeORM supports @OneToMany, @ManyToOne, @ManyToMany, and join tables. Prefer explicit relations options (or QueryBuilder joins) when loading related data to avoid N+1 query issues.

@ManyToOne(() => Organization, (org) => org.users)
organization: Organization;

Migrations Instead of Synchronize

synchronize: true auto-alters the schema from entities and is convenient for local experimentation, but dangerous in production. Use TypeORM migrations so schema changes are reviewable, reversible, and deployable.

Common Mistakes

• Enabling synchronize: true in production environments.
• Forgetting forFeature([Entity]) and getting Repository not found DI errors.
• Using findOne without a where clause (deprecated / ambiguous in modern TypeORM).
• Loading every relation with eager: true and creating unexpected query volume.

Key Takeaways

• @nestjs/typeorm integrates TypeORM connection and repositories into Nest DI.
• Entities map classes to tables; repositories provide typed CRUD helpers.
• Register entities with forFeature in the module that needs them.
• Prefer migrations over schema auto-sync for real environments.