What problems can arise when calling UserRepository.findById() and then iterating over User.getEmails() with forEach(), if the getUsers() method is annotated as @Transactional and the email field is declared as @OneToMany?

The problem arises due to lazy loading (LAZY) of the emails collection in a field annotated with @OneToMany. If the getUsers() method is annotated with @Transactional, then the transaction is only open within that method.

When you call UserRepository.findById(), the User object is loaded, but the emails collection is not initialized immediately (if FetchType.LAZY is used). When attempting to iterate over user.getEmails().forEach() outside of a transaction, Hibernate tries to load the collection, but the session is already closed — resulting in a LazyInitializationException.

To avoid this problem:

• Load the emails collection immediately using FetchType.EAGER (not always recommended due to performance issues).
• Use @Transactional at the method level where the collection is accessed.
• Explicitly initialize the collection within a transaction, for example, by calling Hibernate.initialize(user.getEmails()).

Thus, it is important that access to lazily loaded collections occurs within an open transaction.