Services and Repositories

This skill describes how to structure business logic (services) and data access (repositories).

1. Service layer (business rules)

Services should:

• •Enforce business rules
• •Orchestrate multiple repositories
• •Avoid HTTP-specific types and concerns

Example:

export class UserService {
  constructor(private readonly userRepo: UserRepository) {}

  async create(input: CreateUserInput): Promise<User> {
    const existing = await this.userRepo.findByEmail(input.email);
    if (existing) throw new ConflictError("Email already exists");
    return await this.userRepo.create(input);
  }
}

2. Repository layer (data access)

Repositories should:

• •Encapsulate query construction
• •Hide ORM details from services
• •Provide transaction helpers where needed

export class UserRepository {
  constructor(private readonly db: PrismaClient) {}

  findByEmail(email: string) {
    return this.db.user.findUnique({ where: { email } });
  }

  create(input: CreateUserInput) {
    return this.db.user.create({ data: input });
  }
}

3. When to introduce repositories

Use repositories when:

• •Queries are non-trivial (joins, pagination, filtering)
• •Multiple call sites reuse the same query logic
• •You need better test seams and isolation

If a service is a thin wrapper over a single simple query, a repository may be optional.

Related Skills

• •database-patterns
• •testing-guide