Services in Orionjs encapsulate business logic and provide a clean way to organize your application code. They follow the dependency injection pattern, making your code more modular and easier to test.

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Basic Usage

import {Service} from '@orion-js/services'

@Service()
export class UserService {
  async findById(userId: string) {
    // Implementation...
    return user
  }

  async create(userData: {name: string; email: string}) {
    // Implementation...
    return newUser
  }
}

​
Dependency Injection

Services can be injected into other services or controllers. In v4, you must use the factory function pattern for dependency injection: 
import {Service, Inject} from '@orion-js/services'
import {UserService} from './UserService'

@Service()
export class AuthService {
  // Use factory function for dependency injection
  @Inject(() => UserService)
  private userService: UserService

  async login(email: string, password: string) {
    // Use injected service
    const user = await this.userService.findByEmail(email)
    // Implementation...
    return token
  }
}

​
Circular Dependencies

The factory function pattern used in v4 automatically handles circular dependencies: 
import {Service, Inject} from '@orion-js/services'
import {AuthService} from './AuthService'

@Service()
export class TokenService {
  @Inject(() => AuthService)
  private authService: AuthService

  validateToken(token: string) {
    // Implementation...
  }
}

​
Testing

Services are designed to be easily testable with Jest: 
// In your test
import {mockService} from '@orion-js/services'
import {UserService} from './UserService'
import {AuthService} from './AuthService'

describe('AuthService', () => {
  it('should authenticate valid users', async () => {
    // Mock the dependency
    mockService(UserService, {
      findByEmail: async () => ({
        id: '123',
        email: 'test@example.com',
        password: 'hashed_password'
      })
    })

    const authService = new AuthService()
    const result = await authService.login('test@example.com', 'password')
    
    expect(result).toBeDefined()
  })
})

​
Getting Service Instances

You can get service instances from anywhere in your application: 
import {getInstance} from '@orion-js/services'
import {UserService} from './UserService'

// Get an instance of the service
const userService = getInstance(UserService)

// Use the service
await userService.findById('123')
Services form the backbone of Orionjs applications, providing a structured way to organize business logic and maintain separation of concerns.