Difference Between Update And Saveorupdate In Hibernate

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Update vs saveorupdate hibernate

Update will update the record. Merge also do the same but difference is update raise the error if use record not availale but merge can't instead it will create the record. Check it once. Thankyou1
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Merge: suppose we create a session and load an object. Now object in session cache. If we close the session at this point and we edit state of object and tried to save using update() it will throw exception. To make object persistent we need to open another session. Now we load same object again in current session. So if we want to update present object with previous object changes we have to use merge() method. Merge method will merge changes of both states of object and will save in database.
Update: If we are dealing with any object in same session we should use update() or saveOrUpdate() method.
Hope you will get point.
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If session does not contains an already persistent instance with the same identifier and if you are sure about that then use update to save the data. But merge() method can save your modifications at any time with out having the knowledge about the state of session. 0
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Hi All,
Greetings for the day!
merge() and update() both are used to convert state of an object from detached to persistent but the difference is that if update sees that the object is already present in the session cache then it will throw an exception (NonUniqueObjectException) whereas merge() will not throw any such exception.
Example ---
Session session = sessionFactory.openSession();
Student me = session.get(Student.class, new Integer(101));
session.close();
me.setName('updated Debayan');
Session newSession = sessionFactory.openSession();
Student updatedMe = session.get(Student.class, new Integer(101));
Transaction tx = newSession.beginTransaction();
newSession.update(me); // will throw exception
newSession.merge(me); // will run fine
Explanation --
Here we closed the first session and Student object me became detached. After that we changed the name property of that detached object.
Now if we call update() we will get exception because before reattachment, another instance that represents the same database row has already been loaded into the persistence context of that Session and Hibernate will get confused which object represents the current state.
However, for merge() into updatedMe object, changes of me object will be merged and will finally be saved into the database.
Hope this clarifies the doubts !
Have a great day ahead !!		0
By: Session newSession = sessionFactory.openSession();
Student updatedMe = session.get(Student.class, new Integer(101));
Transaction tx = newSession.beginTransaction();
newSession.update(me); // will throw exception
newSession.merge(me); // will run fine
Explanation --
Here we closed the first session and Student object me became detached. After that we changed the name property of that detached object.
Now if we call update() we will get exception because before reattachment, another instance that represents the same database row has already been loaded into the persistence context of that Session and Hibernate will get confused which object represents the current state.
However, for merge() into updatedMe object, changes of me object will be merged and will finally be saved into the database.
Hope this clarifies the doubts !
Have a great day ahead !!		0
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