What is the difference between save(), persist(), and saveOrUpdate()?

save() returns the generated identifier, persist() returns nothing, and saveOrUpdate() either saves a new object or updates an existing one.

• save() saves the entity and returns its identifier. With an identity column, where the database generates the id, it runs the INSERT at once, even outside a transaction.
• persist() is the Java Persistence API (JPA) method. It does not promise to assign the identifier at once, and it never runs the INSERT outside a transaction.
• saveOrUpdate() checks the identifier, then saves a new entity or updates a detached one, an object whose session has closed.

// save() - returns ID
Long id = (Long) session.save(user);

// persist() - no return value
session.persist(user);

// saveOrUpdate() - smart save/update
session.saveOrUpdate(user);

Hibernate 7 removed save() and saveOrUpdate(). Use persist() for a new object and merge() for a detached one.