Kepiye carane @Transactional mlaku, kalebu propagasi lan rollback?

Question

IT Interview Practice · Accepted Answer

`@Transactional` mbungkus sawijining metode ing transaksi database: Spring mbukak siji sadurunge metode mlaku lan commit nalika bali kanthi normal — utawa **rollback** yen mbuwang error. Ing njero iku minangka **AOP proxy**, sing dadi sumber umume gotcha.

## Panganggo dhasar

```java
@Service
public class TransferService {

@Transactional // commit on success, roll back on RuntimeException
    public void transfer(Long from, Long to, BigDecimal amount) {
        accounts.debit(from, amount);
        accounts.credit(to, amount); // if THIS throws, the debit is rolled back too
    }
}
```

## Aturan rollback default (jebakan klasik)

Kanthi default Spring rollback mung ing exception **unchecked** (`RuntimeException`) lan `Error` — **dudu** ing checked exception. Yen kowe mbuwang checked exception, transaksi *commit*. Timpani kanthi eksplisit:

```java
@Transactional(rollbackFor = Exception.class) // roll back on checked too
public void process() throws IOException { /* ... */ }
```

## Propagasi

Propagasi nemtokake apa sing kedadeyan nalika metode transaksional nyeluk metode liya:

- **REQUIRED** (default): gabung karo transaksi sing nyeluk, utawa miwiti siji yen durung ana.
- **REQUIRES_NEW**: gantung transaksi sing nyeluk lan mlaku ing transaksi anyar sing mandhiri — migunani kanggo log audit sing kudu tetep ana sanajan gawean njaba di-rollback.

```java
@Transactional(propagation = Propagation.REQUIRES_NEW)
public void writeAuditLog(String event) { /* commits independently */ }
```

## Jebakan self-invocation

Amarga `@Transactional` mlaku liwat proxy, nyeluk siji metode `@Transactional` saka metode liya *ing kelas sing padha* ngliwati proxy — anotasi kasebut diabaikan kanthi meneng. Nyeluk lintas bean, utawa suntik dhewe.

## Kenapa iki penting

Transaksi iku papan manggone kebeneran data, mula pewawancara ndhesek keras ing kene. Aturan rollback checked-exception lan bug self-invocation iku rong pitakon sing kanthi andal mbedakake wong sing *nganggo* `@Transactional` karo sing *ngerti* iku.

Panganggo dhasar

Aturan rollback default (jebakan klasik)

Propagasi

Jebakan self-invocation

Kenapa iki penting

Pitakon sing gegandhengan