Hi, I'm not sure if I'm doing my UPDATE's and DELETE's the proper way:

Basically, I want to make sure what I updates, or deletes, in fact exists (ie not deleted by another user) before I actually perform the operation:

Any pointer? Thanks in advance.

You should use Get, not Load for this, because if the object has proxies Load will return a proxy without actually visiting the database to check whether the object exists. But otherwise it should work fine.

Hey Thanks a bunch sergey.

QUESTION 1:
Yes, I tried "Load" then "Update" it gave me weird error complaining another instance with same identifier already exists...? Why is it saying that? I'm trying to UPDATE of course "another" instance would have existed..?

QUESTION 2:
Also, why "NHibernate.ObjectNotFoundException" NOT thrown when the instance I'm trying to update has been deleted by another user? I thought it'd be more intuitive than a generic Hibernate exception.

Well, you don't have to call Update if your object was loaded in the same session, the session already knows about it. As for why that exception is not thrown, I don't know, it was probably this way in H2.0.3 and nobody changed it yet.

So, just:

1. Load(GetType(MyType), UIN)
2. Make changes:
obj.SomeProp = x;
3. o_session.Flush();

That's it? Is this the proper way to do UPDATE? I'd assume you need to wrap Flush inside a transaction AND a try-block in case if object corresponding to the selected UIN has been deleted. Is this ...?

try {
trx = o_session.BeginTransaction();
obj = o_session.Load(GetType(MyType), UIN);
obj.Prop1 = "xxx";
o_session.Flush();
trx.Commit();

} catch(ObjectNotFoundException e) {
//1. alert user object to be updated has been deleted.

//2. in case if you've done other stuff in transaction...
trx.RollBack()l
}

The code you have proposed has a couple of subtle issues. The first issue is that your transaction will only rollback if an ObjectNotFoundException is thrown. However, other exceptions may be thrown as part of executing the try block and if so, your transaction won't rollback until the garbage collector comes and gets it.

The second issue is that you are using exceptions to as part of your regular program execution path. Exceptions in .NET are slow and as such should only be used to handle exceptions rather than control program flow.

I would suggest replacing the try/catch block with a "using" block:

using (trx = o_session.BeginTransaction())
{
...
trx.Commit()
}

Also, I would suggest using the Find method instead of the Get method to load your object if you feel there is a chance that the object may not exist as part of the normal program flow. Then check the Count property on the resultant IList implementation returned. If Count is zero, then alert the user the object has been deleted. Otherwise, set your object to the first item in the list.

Or just use Get, not Load. Get will return null if the object was not found in the database. Also, transaction.Commit will call Flush, so you don't have to call it yourself. But otherwise the code you wrote should work fine.

Thanks guys, that helps.