What are propagation levels in transactions?

Transaction propagation levels in Spring define how methods marked as transactional interact with each other when one calls another. The propagation level determines whether a new transaction should be created, joined, or not used at all.

Main propagation levels in Spring:

• REQUIRED: Uses existing transaction if present; otherwise, creates a new one. This is the default level.

@Transactional(propagation = Propagation.REQUIRED)
public void methodA() { /* ... */ }

• SUPPORTS: Uses existing transaction if present; if not, executes without a transaction.

@Transactional(propagation = Propagation.SUPPORTS)
public void methodB() { /* ... */ }

• MANDATORY: Uses existing transaction; throws exception if none exists.

@Transactional(propagation = Propagation.MANDATORY)
public void methodC() { /* ... */ }

• NEVER: Executes without a transaction; throws exception if a transaction exists.

@Transactional(propagation = Propagation.NEVER)
public void methodD() { /* ... */ }

• NOT_SUPPORTED: Executes without a transaction; suspends any existing transaction.

@Transactional(propagation = Propagation.NOT_SUPPORTED)
public void methodE() { /* ... */ }

• REQUIRES_NEW: Always creates a new, independent transaction; suspends existing one.

@Transactional(propagation = Propagation.REQUIRES_NEW)
public void methodF() { /* ... */ }

• NESTED: Uses existing transaction if present, creating a nested transaction (savepoint). If none exists, behaves like REQUIRED.

@Transactional(propagation = Propagation.NESTED)
public void methodG() { /* ... */ }

Choosing the right propagation level is crucial for proper transaction management and data integrity when transactional methods call each other.