Save and Persist in Hibernate
save()-Save the given
transient instance, first assigning a generated identifier. (Or using the
current value of the identifier property if the assigned generator is used.)
Serializable org.hibernate.Session.save(Object object)
persist()-Make a transient instance
persistent. This operation cascades to associated instances if the association
is mapped with cascade="persist"
void org.hibernate.Session.persist(Object object)
public class HibernateSaveVsPersist {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();
UserDetailsDTO user = new UserDetailsDTO();
user.setUserName("Rahul");
user.setAddress("Comviva A-26, Gurgaon");
/* object a transient instance to persistent,return void*/
session.persist(user);
/* returns
serializable object*/
System.out.println(session.save(user));
session.getTransaction().commit();
}
}
Get and Load in Hibernate-
get() returns data either
from first level cache or from Database where load() return proxy object and
set ID to the proxy object.
When get() method is
called no proxy object is created, hence it is called as early loading.
load()
in hibernate
get() in hibernate
public class HibernateGetVsLoad {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
try {
UserDetailsDTO user1 =
(UserDetailsDTO) session.get(UserDetailsDTO.class, 11);
System.out.println("Using
get() " + user1);
} catch (Exception e) {
System.out.println("Exception
thrown " + e);
}
try {
UserDetailsDTO user2 =
(UserDetailsDTO) session.load(UserDetailsDTO.class, 22);
System.out.println("Using
load() " + user2);
} catch (Exception e) {
System.out.println("Exception
thrown " + e);
}
}
}
get() returns null when object doesn’t found whereas load()
throw exception
Output :
Hibernate:
select userdetail0_.USER_ID as USER_ID1_0_0_, userdetail0_.Address as
Address2_0_0_, userdetail0_.createdOn as createdO3_0_0_,
userdetail0_.description as descript4_0_0_, userdetail0_.USER_NAME as
USER_NAM5_0_0_ from USER_DETAILS_NEW userdetail0_ where userdetail0_.USER_ID=?
Using
get() null
Hibernate:
select userdetail0_.USER_ID as USER_ID1_0_0_, userdetail0_.Address as
Address2_0_0_, userdetail0_.createdOn as createdO3_0_0_,
userdetail0_.description as descript4_0_0_, userdetail0_.USER_NAME as
USER_NAM5_0_0_ from USER_DETAILS_NEW userdetail0_ where userdetail0_.USER_ID=?
Oct 03,
2017 5:26:19 PM org.hibernate.event.internal.DefaultLoadEventListener doOnLoad
INFO:
HHH000327: Error performing load command : org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [com.hibernateInterviewQuestions.UserDetailsDTO#22]
Exception
thrown org.hibernate.ObjectNotFoundException: No row with the given identifier exists:
[com.hibernateInterviewQuestions.UserDetailsDTO#22]
Merge and Update in hibernate
update() throws exception when object it is trying to update is
already available in cache.
public class HibernateUpdateVsMerge {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
UserDetailsDTO user =
(UserDetailsDTO)session.get(UserDetailsDTO.class, 1);
session.close();
/* user object is in detached state now */
user.setUserName("Merge Name-Paras");
Session session2 = sessionFactory.openSession();
/* A different
object with the same identifier
value was already
associated with the session*/
UserDetailsDTO user2 =
(UserDetailsDTO)session2.get(UserDetailsDTO.class, 1);
session2.beginTransaction();
session2.update(user);
session2.getTransaction().commit();
}
}
Hibernate:
select userdetail0_.USER_ID as USER_ID1_0_0_, userdetail0_.Address as
Address2_0_0_, userdetail0_.createdOn as createdO3_0_0_,
userdetail0_.description as descript4_0_0_, userdetail0_.USER_NAME as
USER_NAM5_0_0_ from USER_DETAILS_NEW userdetail0_ where userdetail0_.USER_ID=?
Hibernate:
select userdetail0_.USER_ID as USER_ID1_0_0_, userdetail0_.Address as
Address2_0_0_, userdetail0_.createdOn as createdO3_0_0_,
userdetail0_.description as descript4_0_0_, userdetail0_.USER_NAME as
USER_NAM5_0_0_ from USER_DETAILS_NEW userdetail0_ where userdetail0_.USER_ID=?
Exception
in thread "main" org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already
associated with the session
public class HibernateUpdateVsMerge {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
UserDetailsDTO user =
(UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
session.close();
/* user object is in detached state now */
user.setUserName("Merge Name-Paras");
Session session2 = sessionFactory.openSession();
UserDetailsDTO user2 =
(UserDetailsDTO) session2.get(UserDetailsDTO.class, 1);
session2.beginTransaction();
session2.merge(user);
session2.getTransaction().commit();
}
}
merge()
doesn’t throw exception. It verifies whether the same object is existed in
cache or not. If object exists in cache, then changes are copied into cache
else it will load the values to cache.
