questions:
  - question: "Which language do you prefer? / 어떤 언어로 진행할까요?"
    header: "Language"
    options:
      - label: "한국어"
        description: "한국어로 퀴즈를 풉니다"
      - label: "English"
        description: "Take the quiz in English"
    multiSelect: false

What does this code return? Explain your answer.

@Transactional
fun transfer(from: Long, to: Long, amount: Int) {
    val sender = accountRepository.findById(from).orElseThrow()
    val receiver = accountRepository.findById(to).orElseThrow()
    sender.balance -= amount
    receiver.balance += amount
}
// What happens if amount > sender.balance?

What's wrong with this code? Explain the issue.

@RestController
class UserController(private val userService: UserService) {
    @GetMapping("/users/{id}")
    fun getUser(@PathVariable id: Long): User {
        return userService.findById(id)  // returns null if not found
    }
}

What is the default propagation level of @Transactional in Spring?

Write a REST endpoint that meets these requirements:

- POST /api/users
- Accepts a JSON body with name (String) and email (String)
- Validates that email contains '@'
- Returns 201 Created with the saved user
- Returns 400 Bad Request if validation fails

Correct!

Key point: @Transactional with default propagation (REQUIRED) joins
the existing transaction or creates a new one if none exists.

Not quite. The answer is "REQUIRED".

REQUIRED means: if a transaction exists, join it; if not, create a new one.
This is the most common behavior and Spring's default.

Quiz Results
- Topic: Spring Transaction Management
- Score: 3/5
- Final difficulty: 4/5
- Strengths: @Transactional basics, isolation levels
- Needs work: Propagation types, rollback rules
- Suggestion: Review "transaction propagation" with /backend-study