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Please have a look and let me know whether iam missing anything.

The above sample code is from "EJB 3 in Action" book pages 303 and 304.

So merge operation always attaches the entity to the persistence context? but refresh operation takes the data from the database and updates the same cache & the result will be overwriting the data in the cache 3.

The function is to merge the changes in a managed entity to its corresponding database row. when the transaction ends this data will be written to the database as part of the merge operation, but since this data was overwritten by refresh method the data ultimately written in the database will be the same as before.

@Stateless public class Item Manager Bean implements Item Manager Within the undo Item Changes() method the entity Manager.merge() is called first on the item object before calling the entity Manager.refresh() method.

I understnad that in this instance, the merge() is called before refresh() is to attach the item entity to the persistence context and also that any method invocation on Entity Manager (like merge() or refresh()) will not get executed on the database straight away.

This is not the expected behavior from undo Changes() method right?

Hi The key for the "entity Manager.refresh(entity Manager.merge(item))" is the "flush".

That means the merge() method will not get executed on the database at all, which will stop updating the item record in the database.

Even i was confused when i read the code from the book.

It just does'nt seem appropriate because what is being done in the code seems to deviate from our purpose.

When we execute merge() it will update the databse with the changes.

When we call refresh() it will update the item object with latest data from the database.

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