How to fix org.hibernate.LazyInitializationException - could not initialize proxy - no Session

Getting Transactional

Calling the @Transactional cavalry

Snuggly wrap your data meddling code within a @Transactional boundary to ensure there's always an active Hibernate session in action. Just stick @Transactional over your methods or classes and let Spring handle the rest. Here's an example:

@Transactional
public MyEntity findAndInitialize(Long id) {
    MyEntity entity = entityManager.find(MyEntity.class, id);
    Hibernate.initialize(entity.getLazyCollection()); // Hey Hibernate, wake up!
    return entity;
}
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Spring ensures that the entities are smoothly flushed, and transformations are persisted, without even having to yell "save!"

Transaction propagation and the art of joining

Pay attention to transaction propagation settings. Nested transactions should pop in and join the ongoing transaction party to turn away from the "no session" bouncer at the door.

Configuring the session factory: Get it Right!

Incorrectly setting up your session factory can be an invitation to a closed session disaster. Double-check to ensure the session gets correctly opened and shut within the life of a transaction. You wouldn't want the session dozing off prematurely, would you?

Fetching strategies and the Lazy Initialization Ball

JOIN FETCH: Preemptive strike against LazyInitializationException

Join the JOIN FETCH squad in your HQL/JPQL queries when you know you're going after lazy relations. Why? Because it brings the lazy data home in one neat query:

SELECT p FROM Person p JOIN FETCH p.address WHERE p.id = :id // Fetch, Don't retch!
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Hibernate.initialize: Your ally for eager collections

When fetch joins are out of reach, call out to Hibernate.initialize() to manually wake up lazy collections:

Hibernate.initialize(entity.getLazyCollection()); // Hibernate, rise and shine!
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Give a thought to Data Transfer Objects (DTO)

Consider DTO projection to finally bid adieu to lazy loading. By fetching only what you need, you skirt the overhead of loading the entire entity graph, adding a dash of performance to your app.

Managing sessions and lazy loading

When to open a new session generally

There might be scenarios where you need to swing open a new session. Here, make a call to sessionFactory.openSession() to explicitly kick-start a new session for lazy object initialization. Don’t forget to handle this newfound power responsibly.

Configuration landmine: enable_lazy_load_no_trans

Resist the temptation to toggle on the hibernate.enable_lazy_load_no_trans. This setting is often seen as the last hope when all other options fail. Watch out, as it comes with its bag of potential hazards.

Open session in view: A double-edged sword

Open Session in View (OSIV) might seem like an easy way out of LazyInitializationException, but beware, it could turn into a performance hungry monster. OSIV keeps the database connection up and running throughout the view rendering, ultimately affecting the smooth running of your code.

Efficient query filtering: The unsung hero

Filter your queries efficiently to minimize the data load on lazy models. Utilize both WHERE clauses and DTO projection to streamline your data access, cutting down the likelihood of running into a LazyInitializationException.