Hibernate version: 3.2.5

We've being using Hibernate for many years now and we love it. Recently, we found that the Hibernate Entity Manager - when asked to merge using a long transaction - will actually load the object again from the database (if its not available in the first or second level cache). Why does it do this? Why does it not simply use the detached object? Hibernate saveOrUpdate doesn't load the object, why does merge?

In addition to inefficiency, this causes problems when you load object using native queries. Hibernate will generate its own query during merge and this may clash with the mapping.

I miss the older, simpler Hibernate days...

It has something to do with semantics of merge. It is hard for a container to track all changes in an object while it has been detached. Look at section 10.7. Automatic state detection of hibernate documentation. You might want to use a different method rather than merge.


Farzad-

There is no other method for updating. I just don't understand why Hibernate can't use the detached object itself. So a complex object graph will now get loaded before each update? There's got to be a better way...

There are actually several other methods for updating an entity: persist, save, saveOrUpdate, and replicate.

The real question is what are you trying to do?

The merge method is designed to update the database, without re-associating the instance with the Session (it is expected that it is already associated with the session).

The persist method will write out the instance.

The save will persist the object to the database and generate a new ID in the process. (Should be a new instance <read "row" > for the table.

The update will take an existing object and update that row in the database based on the ID of the object

saveOrUpdate: will do save or update depending on the state of the object.

I believe, that save, update, and saveOrUpdate all re-associate the object with the session (someone correct me if i'm wrong). I've run into a Hibernate error where there already exists an instance with a particular ID associated with the Session. I'm not sure if my solution for this problem is correct but: check for this error and run a merge() to persist my info.

Hope this helps.

-B

I am using Hibernate Entity Manager, not Session. The only method to update from Entity Manager is merge. Of course, I can write a Entity Manager proxy and redirect to Session.saveOrUpdate, but I was wondering about the design approach. Why did Hibernate decide to load before update? At least in core Hibernate you can control this with the select-before-update setting for class.

Sorry, I misunderstood the question/situation. I think that this question would best be posed in the other forum (Hibernate Annotations, EntityManager, Search, Validator, Shards). I only say that because I noticed that one of the Hibernate Team seems to monitor that one closely (emmanuel), at least they have since i posed my question and have been watching for a response over the last few days.

-B

Thanks. Silly of me...

Here is emmanuel's response: viewtopic.php?p=2371627