Prev [Solved] org. Next Hibernate SessionFactory. Pankaj I love Open Source technologies and writing about my experience about them is my passion. Follow Author. Comments Richard B Turgid says:. June 10, at pm. Abhineet says:. May 12, at am. Sachin says:. November 20, at pm.
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August 11, at am. August 10, at pm. Ravi Kumar says:. July 21, at pm. Pankaj says:. Deepti chaudhary says:. May 19, at am. Anshuman Dwivedi says:. Hibernate handles persisting any changes to objects in the session when the session is flushed. Merge should be used in that case.
It merges the changes of the detached object with an object in the session, if it exists. Update: Suppose we are dealing with any employee object in the same session then we should use update or saveOrUpdate method. Update: if you are sure that the session does not contains an already persistent instance with the same identifier,then use update to save the data in hibernate. Merge: Suppose we are creating a session and load an employee object.
Now object in session cache. I understand that update is used to put a detached object into persistent state if no other object with the same id and type is attached to the session. Merge doesn't care about states. It just returns a persisted object of the same type if it doesn't exist in the session or it updates the old object with the values of the new object. My questions is regarding database hits. Does the method 'update' and 'merge' hit the database immediately?
Edit: What happens if we call the update method on a persisted instance by the save method?. I thought the update method was just used on detached instances.
Hibernate handles persisting any changes to objects in the session when the session is flushed. Merge should be used in that case. It merges the changes of the detached object with an object in the session, if it exists. Update: if you are sure that the session does not contains an already persistent instance with the same identifier,then use update to save the data in hibernate. Merge: if you want to save your modifications at any time with out knowing about the state of an session, then use merge in hibernate.
When the entity instance is in the persistent state, all changes that you make to the mapped fields of this instance will be applied to the corresponding database records and fields upon flushing the Session. The actual saving of data to the database occurs on committing the transaction or flushing the Session.
In case of merge: When we call merge method on detached instance, it will update it with updated value. In case of update When we call update method on detached instance, it will give exception org. In this case, you can use session. You can use one of the refresh methods on the Session interface to refresh an instance of a persistent object Method merge does exactly opposite to what refresh does i. Otherwise, it will update the object.
The existing database table is like below; I am going to update the values in the student table using the update method :. When we call update method, if already a session cache containing the same object then the update method throws an exception called NonUniqueObjectException.
Like update method merge is also used to transfer an object from detached stated to persistent state. If we call merge method, then it verifies whether the same object has existed in the session cache or not. If the object has lived in the cache, then the current changes are copied into the cache; otherwise, it will load the values to cache.
When we call update method, if the object already existed in cache update method will throw an exception whereas merge method copies the changes into the cache. Very detailed and neat explanation. I can able to understand concepts clearly.
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