What is the difference between a service and a repository in NestJS?

Q: What is the difference between a service and a repository in NestJS?

@Injectable() export class UsersService { constructor( @InjectRepository(User) private readonly usersRepository: Repository , ) {} async findActiveUsers(): Promise { // Business logic lives here return this.usersRepository.find({ where: { isActive: true }, order: { createdAt: 'DESC' }, }); } async deactivateUser(id: number): Promise { const user = await this.usersRepository.findOneOrFail({ where: { id } }); user.isActive = false; await this.usersRepository.save(user); } } Service — owns business rules, validation logic, and orchestration. Repository — owns data access: queries, inserts, updates, transactions. This separation makes services easier to unit test (mock the repository). TypeORM provides Repository via @InjectRepository() out of the box.

Difficulty: 5/10

service layer, repository pattern, dependency injection

A service contains business logic and orchestrates calls to repositories, other services, or external APIs. A repository is a data-access abstraction that handles persistence concerns such as queries and transactions. Services are injected with repositories — this keeps business logic and data access cleanly separated.

Service using an injected repository

Separation of concerns:

1
Service — owns business rules, validation logic, and orchestration.
2
Repository — owns data access: queries, inserts, updates, transactions.
3
This separation makes services easier to unit test (mock the repository).
4
TypeORM provides Repository<Entity> via @InjectRepository() out of the box.

Scenario Questions

0-2 years experience

1You need to fetch a list of users in a NestJS controller. Would you call the repository directly or go through a service, and why?
2If you accidentally inject a repository into a controller instead of a service, what runtime issues might you encounter?
3Describe how you would set up a simple CRUD module using both a service and a repository.

Follow-up Questions

Can you give an example of a method that belongs in a service versus one that belongs in a repository?
How does this separation affect your unit testing approach?
What would change if you added a caching layer to the data access flow?