updating obj property, updates database How to avoid this?

oalexandrino · **Posted:** Thu Aug 30, 2007 9:28 pm

Hello all,

Please, have a look at this code and tell me what's happening and why.

Code:

//first, i create a businnes object and define its ID
BusinessObject obj = new BusinessObject (id);

// secondly, I use NHibernateSession in order to get that object with the data stored in the database
BusinessObject obj = NHibernateSession.Get(obj);   

obj.Property = "new value";

...
...
...
last code of the page


after I have defined a new value to property it's called other codes of the application, but NHibernateSession  is never called so that to update the new value in the database.

but when I take a look at database the data is updated.

I wouldn't like to leave this behavior...in my case I use NHibernateSession to update explicitly.

So, How to avoid that ? 

karlchu · **Posted:** Thu Aug 30, 2007 11:28 pm

In the same session, if you load/get an entity, update its property, then flush the session (either explicitly or implicitly). The updates to the entity will get propagated to the database; no explicit call to Update() is needed. If you don't want that behavior, call ISession.Evict() to remove the entity some time before the session is flushed.

oalexandrino · **Posted:** Fri Aug 31, 2007 9:04 am

I see...

would be it ?

Code:

BusinessObject obj = NHibernateSession.Get(obj);    

obj.Property = "new value";

NHibernateSession.Evict() 

that would avoid "BusinessObject" update and all other ones in the Session?

how to "flush" and "evict" just a specif object that is in the section?

thanks!

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karlchu · **Posted:** Fri Aug 31, 2007 9:54 am

You pass the object to be evicted to Evict() like this:

Code:

NHIbernateSession.Evict(obj);

oalexandrino · **Posted:** Fri Aug 31, 2007 10:06 am

THANKS a million.

I didn't know that method.

Chapter 15.3. Managing the caches tells all what I was needing

just one more think..

do you think the synchronization by default wouldn't an overhead to NHibernate?

Imagine you're in a presentation layer...where no update will propagate to database...I think it's a good idea evict completely all objects from the session cache ( or a few of them)

karlchu · **Posted:** Fri Aug 31, 2007 10:24 am

When the session is closed, the entities cached in it are correspondingly discarded. If you follow the recommendation of making sure a session is short-lived, it generally would not be a concern.

If you want to have (or fake) a read-only session, you can set the FlushMode of the session to Never, and make sure you don't call Flush() before you close the session.

jlockwood · **Posted:** Thu Sep 13, 2007 8:38 pm

You could also set FlushMode to commit after opening the session.
session.FlushMode = FlushMode.Commit;

That way you will only have flushes on Commits. karlchu is right though, you need short lifespans for your sessions, or put in place a mechanism for shared transactions. Having to use Evict is (to me at least) a sign that you aren't managing session/transaction contexts well. I rarely ever use that method.

jlockwood · **Posted:** Thu Sep 13, 2007 8:39 pm

sorry for repeat