How do you seed a database in a NestJS application?

Q: How do you seed a database in a NestJS application?

@Injectable() export class DatabaseSeeder { constructor( @InjectRepository(User) private userRepo: Repository , @InjectRepository(Role) private roleRepo: Repository , ) {} async seed(): Promise { const existing = await this.roleRepo.count(); if (existing > 0) return; // idempotent — skip if already seeded const adminRole = await this.roleRepo.save({ name: 'admin' }); const userRole = await this.roleRepo.save({ name: 'user' }); await this.userRepo.save({ email: 'admin@example.com', password: await bcrypt.hash('Admin123!', 12), role: adminRole, }); console.log('Database seeded successfully'); } } // Lifecycle-based seeding — runs on app bootstrap @Module({ providers: [DatabaseSeeder, TypeOrmModule.forFeature([User, Role])] }) export class SeedModule implements OnApplicationBootstrap { constructor(private seeder: DatabaseSeeder) {} async onApplicationBootstrap() { if (process.env.NODE_ENV !== 'production') { await this.seeder.seed(); } } } // Standalone script — run independently of the HTTP server async function seed() { const app = await NestFactory.createApplicationContext(SeedModule); await app.get(DatabaseSeeder).seed(); await app.close(); } seed(); Always make seed() idempotent — check existence before inserting so re-runs are safe. Guard production seeding with a NODE_ENV check or a dedicated SEED_DATABASE flag. NestFactory.createApplicationContext() creates a minimal app without starting the HTTP server — perfect for scripts. Use bcrypt to hash seed passwords — never store plain text even in development data. Place seed scripts in a seeds/ directory and add them to package.json scripts for easy invocation.

Difficulty: 5/10

database seeding, NestJS modules, typeorm

Create a DatabaseSeeder service with seed() methods that use idempotent checks before inserting. Run it via OnApplicationBootstrap in non-production environments or as a standalone NestJS application context invoked by a separate CLI script. Idempotency prevents re-seeding on restart.

Idempotent seeder with bootstrap and standalone modes

Database seeding best practices:

1
Always make seed() idempotent — check existence before inserting so re-runs are safe.

How do you seed a database in a NestJS application?

Difficulty: 5/10

database seeding, NestJS modules, typeorm

Create a DatabaseSeeder service with seed() methods that use idempotent checks before inserting. Run it via OnApplicationBootstrap in non-production environments or as a standalone NestJS application context invoked by a separate CLI script. Idempotency prevents re-seeding on restart.

Idempotent seeder with bootstrap and standalone modes

Database seeding best practices:

1
Always make seed() idempotent — check existence before inserting so re-runs are safe.

How do you seed a database in a NestJS application?

Create a DatabaseSeeder service with seed() methods that use idempotent checks before inserting. Run it via OnApplicationBootstrap in non-production environments or as a standalone NestJS application context invoked by a separate CLI script. Idempotency prevents re-seeding on restart.

How do you seed a database in a NestJS application?

Create a DatabaseSeeder service with seed() methods that use idempotent checks before inserting. Run it via OnApplicationBootstrap in non-production environments or as a standalone NestJS application context invoked by a separate CLI script. Idempotency prevents re-seeding on restart.

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