Ho boy, I bet this question has been answered millions of times, but searching the forums turned up so many irrelevant posts that I gave up.

Basically, when should I use SaveOrUpdate versus Flush?

When I create a new object, I commit it to the database with SaveOrUpdate.
When I update an object, do I use Flush or SaveOrUpdate?

So far I had been using SaveOrUpdate most of the time, but I am worried it is wrong.

Also, when is it pertinent to do a Flush? I'm using NH in a web application and I was wondering if doing a single Flush just at the end of the page processing would be sufficient or there would be situations where it would cause a problem?

Thanks for your help. I am trying to improve the performance of my stuff and I'd like to learn some best practices at the same time.

Alain-Daniel

Flush() and SaveOrUpdate() are different concepts.

Use Update() if the entity is a detached object; i.e. the object is not associated with the session anymore. That means it one of three things: the object has been loaded from a different session; you have cleared the session; or you have evicted the object from the session. Update() or Lock() to re-associate the object with the session.

Use Save() if the entity is a transient object; i.e. the object is brand spanking new.

Use SaveOrUpdate() if you don't know if the object is new or not.

In all of the above cases, you may still need to call Flush(). Flush() basically synchronize the session with the database. In other words, Flush() flushes any pending operation that has not been pushed to the database.

If you use transactions, you almost never need to call flush as it is automatically called on commit.