Updating in hibernate
In this tutorial, I am discussing few thoughts around method present in hibernate session class. It updates the database with values from a detached entity.
Sometimes we face situation where we application database is modified with some external application/agent and thus corresponding hibernate entity in your application actually becomes out of sync with it’s database representation i.e. Refresh method was updating the entity with latest database information. Merging is performed when you desire to have a detached entity changed to persistent state again, with the detached entity’s changes migrated to (or overriding) the database.
The given instance does not become associated with the session.
This operation cascades to associated instances if the association is mapped with cascade=”merge”.
Modifications made after this are detected and if dynamic-update="true" only the modified properties are included in the SQL.
I tried it once and it worked for simple properties, but it felt a bit unsafe with collections and associations, so I gave up the idea.
When we have a bidirectional relationship between objects, it means that we are able to access Object A from Object B, and Object B from Object A. This means that we need to populate both the Note: To observe best coding practices, the code I’ve put into this Controller class is usually best placed in a Service class, but to keep things as simple as possible for this tutorial I’ve just placed all the code directly into the Controller. When you do you’ll instantly receive one free gift from me (and plenty more in the future).
No need to call save Or Update() or any other method.update your save Orupdate method like thispublic T save Or Update(T entity) and keep the dynamic-update=true, and you won't need that select-before-update on your mapping. But I think if you have to enable optimistic locking, this won't work.
The method signatures for the merge operations are: Copy the state of the given object onto the persistent object with the same identifier.
If there is no persistent instance currently associated with the session, it will be loaded. If the given instance is unsaved, save a copy of and return it as a newly persistent instance.
In above example, ‘merged Persistent Emp Entity’ is new entity which is persistent.
So if you want to any more change, then make in in ‘merged Persistent Emp Entity’ instance.