@Transactional Basics

@Transactional is a Spring annotation that wraps a method in a database transaction through an AOP proxy that begins before the method runs, commits on success, and rolls back on a RuntimeException.

Declarative transaction management uses @Transactional and lets the AOP proxy handle everything, while programmatic management uses TransactionTemplate for explicit begin, commit, and rollback control in code.

Class-level @Transactional sets the default for all public methods, and method-level @Transactional overrides it for that specific method.

Without Spring you manually manage Connection.setAutoCommit(false), commit(), rollback(), and close() in try-catch-finally, while Spring's @Transactional replaces all of that with one annotation through an AOP proxy.

@Transactional(readOnly = true) tells Spring and Hibernate that the transaction will only read data, enabling optimizations like skipping dirty-checking and routing to a read replica, but it is a hint, not a hard write-prevention guarantee.

@Modifying marks a @Query as an UPDATE or DELETE so Spring calls executeUpdate(), and clearAutomatically = true clears the stale persistence context afterward so reads fetch fresh data from the database.

Always put @Transactional on the implementation class, not the interface, because Spring Boot defaults to CGLIB proxies which subclass the concrete class and may not see annotations on interfaces.