How do I get auto generated id in hibernate 7?

How do I get the auto-generated id in Hibernate 7?

I have an entity with

@Id @GeneratedValue(strategy=jakarta.persistence.GenerationType.IDENTITY) public int id;

How do I create an object of this type and get the id?

In Hibernate 5/6, I could use session.save and that would write the id value back to the id field in my object.

But in Hibernate 7, session.save has been replaced with session.persist, which doesn't write the id back to the object before it returns. So what do I do if I need the auto-generated id without committing the transaction?

Solution

In Hibernate 7, you're correct that session.persist() is now preferred over session.save(), but there's an important distinction between the two:

session.persist(entity) does not return the generated ID or trigger it immediately.
session.save(entity) (used in Hibernate 5/6) would return the generated ID and populate the entity’s @Id field immediately.

The Problem:

In Hibernate 7, using persist() does not guarantee immediate ID generation. The ID is usually assigned during the flush, which typically happens:

When the transaction is committed, or
When session.flush() is explicitly called.

The Solution:

If you want to get the auto-generated ID before committing the transaction, you need to manually trigger a flush:

MyEntity entity = new MyEntity();
session.persist(entity);
session.flush(); // Triggers insert, and ID gets generated
int id = entity.getId();

Now entity.getId() will return the auto-generated ID from the database. Why the Change?

Hibernate 7 emphasizes JPA compliance, and persist() is a JPA standard that defers database interaction until flush time. save() was a Hibernate-specific shortcut that tightly coupled ID generation with method return — convenient, but not portable. Summary

Use session.persist(entity) to store the entity.
Use session.flush() if you need the ID before committing.