Java.Hibernate.if we have transactional inside transactional how will it work ?

✅ When you call a @Transactional method from another @Transactional method in the same bean (or same Spring proxy):

• By default, Spring uses propagation REQUIRED, which means:
  • The inner @Transactional method joins the existing transaction of the outer method.
  • There’s still only one physical transaction and one session.
  • Both methods share the same first-level cache/persistence context → batch fetching can work as long as the session stays open.

@Transactional
public void outerMethod() {
    List<Author> authors = em.createQuery("FROM Author", Author.class).getResultList();
    for (Author author : authors) {
        innerMethod(author); // transactional inside transactional
    }
}

@Transactional
public void innerMethod(Author author) {
    List<Book> books = author.getBooks(); // shares same transaction/session with outerMethod
    ...
}

✔ In this case, since both methods are called within the same proxy, and default propagation is REQUIRED, innerMethod runs inside the same transaction/session → batch fetching can work.

🚨 BUT there’s a catch:

Self-invocation → if you call this.innerMethod(...) inside the same class, Spring’s proxy-based AOP will not apply the transactional behavior to the inner method, and your @Transactional on innerMethod will be ignored entirely!

✅ To make nested transactions effective, you need:

• Either the calls to go through a Spring proxy (e.g., call methods on another bean),
• Or use AOP-aware mechanisms like ApplicationContext.getBean(ThisClass.class).innerMethod(...)

🟢 Summary of key behaviors:
1️⃣ Transactional inside transactional, same proxy, default propagation (REQUIRED) → inner joins outer transaction → same session → batching can work.
2️⃣ Transactional with different propagation (e.g., REQUIRES_NEW) → inner opens new transaction → new session → batching won’t work across them.
3️⃣ Transactional inside same class by self-call → ignored → inner @Transactional won’t apply unless the call goes through Spring’s proxy.

🔥 Bottom line:

In Spring, nested @Transactional methods with propagation REQUIRED share the same transaction/session, enabling batch fetching; but self-invocation can silently break transactional behavior.