1. Background: Transactions and Hibernate Sessions

• What is a transaction?

  A transaction (@Transactional in Spring) is a unit of work with the database.

  Inside it:

  • A Hibernate Session is open.
  • Queries can run.
  • Lazy associations can be fetched if needed.

  Outside it:

  • The Session is closed.
  • Entities are still available in memory, but lazy fields cannot trigger new queries anymore.

• Why does this matter?

  In Hibernate/JPA, relationships like @OneToMany are usually lazy by default.

  Example:

  @Entity
  class User {
      @OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
      private Set<Offer> offers;
  }
  
  

  When Hibernate loads a User, it doesn’t load offers. Instead, it puts a proxy object (PersistentSet) in place.

  That proxy can only be initialized if a Session is open.

2. Lazy Loading Explained

• Lazy association = loaded on demand.

  User user = userRepository.findById(id).orElseThrow();
  user.getOffers(); // not loaded yet
  int size = user.getOffers().size(); // triggers SELECT * FROM offers ... if inside a tx
  
  

• What happens outside a transaction?

  If you call .size() (or loop, or access fields) on that proxy:

  • Hibernate wants to run SQL.

  • But the Session is closed.

  • Hibernate throws:

    org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    
    

3. What Happened in Our Code

We added logging inside OfferAdminMapperDecorator:

try {
    loggingService.info(LogPrefix.OFFER, LogLayer.MAPPER,
        "User {} offers size: {}", user.getId(),
        (user.getOffers() == null ? "null" : user.getOffers().size()));
} catch (LazyInitializationException e) {
    loggingService.error(LogPrefix.OFFER, LogLayer.MAPPER,
        "Could not initialize user.getOffers() for user {}: {}", e, user.getId(), e.getMessage());
}

• userQueryAdminService.getUserEntityById(...) returns a User.
• At this point, User.offers is still a lazy proxy.
• Our mapper is not annotated with @Transactional, so the Session is already closed.
• .size() tries to run SQL but fails → LazyInitializationException.

That’s why our logs look like:

Could not initialize user.getOffers() for user [...] failed to lazily initialize a collection

The same thing happened for:

• org.getOffers().size()
• emp.getCreatedOffers().size()