Question
How do I resolve the 'failed to lazily initialize - no session or session was closed' error in Hibernate and Spring?
@Entity
public class User {
@Id
private Long id;
@OneToMany(fetch = FetchType.LAZY)
private List<Order> orders;
}
Answer
The 'failed to lazily initialize - no session or session was closed' error occurs in Hibernate when you try to access a lazily-loaded collection outside an active Hibernate session. This article explains how to troubleshoot and resolve this error effectively.
@Transactional
public List<User> getUsersWithOrders() {
return userRepository.findAll();
}
Causes
- Accessing lazily-loaded associations after the Hibernate session has been closed.
- Not managing transaction boundaries correctly in a Spring application.
- Misconfigured fetch type settings for entity relationships.
Solutions
- Ensure that the Hibernate session is open when accessing lazily-loaded collections by using appropriate transaction management.
- Use Eager fetching for collections if you always need the data without a session open.
- Implement a service layer where data retrieval is handled within a session context.
Common Mistakes
Mistake: Closing the Hibernate session before accessing lazy-loaded fields.
Solution: Ensure that the session remains open by fetching data within a @Transactional method.
Mistake: Assuming Eager fetching is the best approach for all scenarios.
Solution: Use Eager fetching judiciously to avoid performance issues; use Lazy fetching when you want to optimize data loading.
Helpers
- Hibernate lazy initialization error
- Spring Hibernate error solutions
- fix Hibernate no session error
- lazy loading in Hibernate
- Spring transaction management
