SessionFactory API

getCurrentSession vs openSession

• public Session openSession() throws HibernateException

  Opens a NEW session from SessionFactory, which has to be explicitly closed by programmer.

• public Session getCurrentSession() throws HibernateException

  Opens new session if one doesn’t exist, otherwise continues with the existing one.

  Gets automatically closed upon Tx boundary (commit/rollback) or thread over (since current session is bound to current thread as specified in hibernate.cfg.xml property current_session_context_class=thread)

Session API - CRUD Operations

1. Save Operation

public Serializable save(Object o) throws HibernateException

(Deprecated in Hibernate 6)

• Input: Transient POJO reference (not yet persistent)
• Returns: Serializable ID auto-generated by Hibernate, associated with the PERSISTENT entity
• Behavior: Auto persists transient POJO on the DB (upon committing tx) & returns unique serializable ID generated by Hibernate framework (if @GeneratedValue is used for id)
• Null ID: Creates a new ID and inserts a row
• Non-null ID (existing or non-existing): Ignores passed ID, creates its own ID & inserts a row

2. Persist Operation

public void persist(Object transientRef)

• Input: Transient POJO reference
• Behavior: Makes transient object persistent
• Non-null ID: Throws org.hibernate.PersistentObjectException: detached entity passed to persist

3. SaveOrUpdate Operation

public void saveOrUpdate(Object ref)