Session interface important methods
get(),load(),evict(),update() and merge()
public class
HibernateGetVsLoad {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
UserDetailsDTO user1=
(UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
System.out.println(user1.getUserName());
System.out.println(user1.getAddress());
System.out.println(user1.getDescription());
UserDetailsDTO user2=
(UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
System.out.println(user2.getUserName());
System.out.println(user2.getAddress());
System.out.println(user2.getDescription());
}
}
Existing
Database
select * from USER_DETAILS_NEW
Scenario 1: When Hibernate is using first level caching.
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey
,Hibernate is Amazing
Paras
722/18
Shastri Nagar , Rohtak
Hey
,Hibernate is Amazing
Scenario 2: calling evict() and removing user1 object from cache
public class
HibernateGetVsLoad {
public static void main(String[] args) {
SessionFactory sessionFactory =
new
Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
UserDetailsDTO user1=
(UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
System.out.println(user1.getUserName());
System.out.println(user1.getAddress());
System.out.println(user1.getDescription());
session.evict(user1);
//session.clear();
//session.flush();
UserDetailsDTO user2=
(UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
System.out.println(user2.getUserName());
System.out.println(user2.getAddress());
System.out.println(user2.getDescription());
}
}
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey
,Hibernate is Amazing
Hit Again to Database
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey ,Hibernate is
Amazing
Scenario 3 calling session.clear();
clears everything within a session
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey
,Hibernate is Amazing
Hit Again to Database
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey ,Hibernate is
Amazing
Scenario 4 – When Id
doesn’t exist and we’re calling session.get()
UserDetailsDTO user1= (UserDetailsDTO) session.get(UserDetailsDTO.class, 1);
UserDetailsDTO user2= (UserDetailsDTO) session.get(UserDetailsDTO.class, 3);
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=?
Paras
722/18
Shastri Nagar , Rohtak
Hey
,Hibernate is Amazing
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" java.lang.NullPointerException
at
com.hibernateInterviewQuestions.HibernateGetVsLoad.main(HibernateGetVsLoad.java:23)
Scenario 5: get()
and load() when entry doesn’t exist
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, 3);
System.out.println("Using
get() "+user1);
} catch (Exception e) {
System.out.println("Exception
thrown " +e);
}
try {
UserDetailsDTO user2 =
(UserDetailsDTO) session.load(UserDetailsDTO.class, 3);
System.out.println("Using
load() "+user2);
} catch (Exception e) {
System.out.println("Exception
thrown " +e);
}
}
}
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=?
Exception
thrown org.hibernate.ObjectNotFoundException: No row with the given identifier exists:
[com.hibernateInterviewQuestions.UserDetailsDTO#3]
Difference between get() and load()
1. Behavior when Object is not found in Session
Cache
Apart from performance this is another
difference between get and load which is worth remembering. get method of
Hibernate Session class returns null if object is not found in cache as well as
on database while load() method throws ObjectNotFoundException if object is not found on cache as well as on database but
never return null.
2. Database hit
Get method always hit database while load() method may not always
hit the database, depending upon which method is called.
3. Proxy
Get method never returns a proxy, it either
returns null or fully initialized Object, while load() method may return
proxy, which is the object with ID but without initializing other properties,
which is lazily initialized. If you are just using returned object for creating
relationship and only need Id then load() is the way to go.
4. Performance
By far most important difference between get and
load in my opinion. get method will return a completely initialized object
if Object is not on the cache but exists on Database, which may involve multiple
round-trips to database based upon object relational mappings while load() method of Hibernate
can return a proxy which can be initialized on demand (lazy
initialization) when a non identifier method is accessed. Due to above reason
use of load method will result in slightly better performance, but
there is a caveat that proxy object will throw ObjectNotFoundException later if
corresponding row doesn’t exists in database, instead of failing immediately so
not a fail fast behavior.
5. load method exists prior to get method which
is added on user request.
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