Using Repos

Repos (repositories) handle data access and external adapters. They are usually called by services.

Creating a Repo

Let’s refactor the service from the previous guide to use a repo:

import { Vla } from 'vla'

class UserRepo extends Vla.Repo {
  async findById(id: string) {
    const db = new Database()
    return db.users.find({ id })
  }
}

class UserService extends Vla.Service {
  repo = this.inject(UserRepo)
  session = this.inject(SessionService)

  async getProfile(userId: string) {
    // Services handle authorization
    if (this.session.currentUserId !== userId) {
      throw new Error('Unauthorized')
    }

    // Repos handle data access
    const user = await this.repo.findById(userId)

    return {
      name: user.name,
      email: user.email,
      joinedAt: user.createdAt
    }
  }
}

Built-in Memoization

Repos have a built-in this.memo() helper for memoization. This automatically caches method results within a request:

class UserRepo extends Vla.Repo {
  // Memoized method - only executes once per unique ID during a request
  findById = this.memo((id: string) => {
    const db = new Database()
    return db.users.find({ id })
  })
}

// Multiple calls with the same ID = only one database query
await repo.findById('1') // Executes query
await repo.findById('1') // Returns cached result
await repo.findById('2') // Executes new query

Learn more about memoization in the Memoization guide.

Key Characteristics

• Repos should not be aware of context like sessions
• Repos don’t check for authorization. That’s the service’s responsibility
• Repos don’t call services
• Repos can call other repos. When doing so, it’s good practice to create a separate repo that combines multiple repos
• Repos have a scope of invoke, meaning all usages during a request share the same instance. This is how memoization works across your entire application
• Repos can call the database directly, but should use a resource for better infrastructure management (covered in the next guide)

Next Steps

For long-lived infrastructure clients like database pools, use Resources.