@Transactional hufanyaje kazi, pamoja na propagation na rollback?

Question

IT Interview Practice · Accepted Answer

`@Transactional` hufunga method ndani ya transaction ya database: Spring hufungua moja kabla method haijakimbia na hu-commit inaporudi kwa kawaida — au **hu-rollback** ikiwa itatupa. Ndani ya pazia ni **AOP proxy**, ambayo ni chanzo cha gotchas nyingi.

## Matumizi ya kimsingi

```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
    }
}
```

## Kanuni ya rollback ya chaguo-msingi (mtego wa kawaida)

Kwa chaguo-msingi Spring hu-rollback tu kwenye exceptions **zisizokaguliwa (unchecked)** (`RuntimeException`) na `Error` — **si** kwenye checked exceptions. Ukitupa checked exception, transaction *hu-commit*. Ipitishe (override) kwa uwazi:

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

## Propagation

Propagation huamua kinachotokea wakati method ya transactional inaita nyingine:

- **REQUIRED** (chaguo-msingi): jiunge na transaction ya mwitaji, au anzisha moja ikiwa haipo.
- **REQUIRES_NEW**: simamisha transaction ya mwitaji na kimbia ndani ya moja mpya, huru — muhimu kwa audit logs ambazo lazima zidumu hata kama kazi ya nje itafanya rollback.

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

## Mtego wa self-invocation

Kwa sababu `@Transactional` hufanya kazi kupitia proxy, kuita method moja ya `@Transactional` kutoka method nyingine *ndani ya class ileile* hupita proxy — annotation hupuuzwa kimya kimya. Ita kuvuka beans, au jiingize mwenyewe (inject self).

## Kwa nini ni muhimu

Transactions ndipo usahihi wa data unapoishi, hivyo wahoji husukuma kwa nguvu hapa. Kanuni ya rollback ya checked-exception na bug ya self-invocation ndizo maswali mawili yanayowatofautisha kwa uhakika watu waliotumia `@Transactional` na wale wanaoielewa.

Matumizi ya kimsingi

Kanuni ya rollback ya chaguo-msingi (mtego wa kawaida)

Propagation

Mtego wa self-invocation

Kwa nini ni muhimu

Maswali yanayohusiana