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Object entity1 is still detached but the changes have been merged into entity2 - the object in session's Persistent Cache.
As the data had been modified, Hibernate also schedules an update query on the object, thus reflecting the changes made to entity1 when it was in the detached state.
rows in the database), or if a lot of data is needed to construct an entity object.
In the latter case, it may require too many resources to assemble an entity object just to change the value of a single field, for instance.
I had to read the JPA spec (1.0, but I guess it should be unchanged in 2.0) in order to get the following: Message msg = new Message(); Text("Foo"); Message msg2 = em.merge(msg); println("New, transient object: " msg); println("Merged object: " msg2); Message msg3 = em.merge(msg2); println("Merging persistent object: " msg3); Message msg4 = new Message(); msg4Text("Bar"); msg4Id(msg3Id()); Message msg5 = em.merge(msg4); println("Detached entity with same id: " msg5); println("Merged text: " msg5Text()); em.clear(); Message msg6 = em.merge(msg5); println("Merged detached entity: " msg6); New, transient object: model. [email protected] Merged text: Bar Hibernate: select message0_as id1_1_, message0_.author Id .....
This is applicable for situations where triggers are /// utilized, so that any changes resulting from the triggers will be reflected in the returned /// object instance.
For those who want Hibernate to manage the last modified date column but don't want optimistic locking, another alternative is to use an event listener to set the last Modified property.
I happened upon this solution before discovering the versioning solution.
Managing create date is easily accomplished by initializing create date via the constructor.
Example: In addition to autopopulating the "last Modified" property, @Version will enable optimistic locking.If entity1 had no changes then the update query will not be fired.