Persistent Object: An object with an id existing in the database that we pulled to the session.
Transient Object: An object with no id that has not yet been persisted.
Detached Object: It is the object that is formed as a result of closing the Session to which the persistent object is connected. The object's id field is full and probably corresponds to a record in the database.
! After hibernate3, the default value lazy is set to "true".
"By default, Hibernate3 uses lazy select fetching for collections and lazy proxy fetching for single-valued associations."
Lazy initialization exception
Fires if there is access to the detached object after commit. For example:
{s = sessions.openSession();Transaction tx = s.beginTransaction();Hibernate.initialize();User u = (User) s.createQuery("from User u where u.name=:userName").setString("userName", userName).uniqueResult();Map permissions = u.getPermissions();tx.commit();s.close();Integer accessLevel = (Integer) permissions.get("accounts"); // Error! Attempting to access detached object.}
"Hibernate does not support lazy initialization for detached objects"
If we use non-lazy links (lazy="false") too much, we draw too many objects into memory. Instead, it may make more sense to use join fetch (non-lazy fetch) in the tansactions we want.