How should NHibernate update properties mapped as Version

Using fluent NHibernate I have a property on a class mapped using Version

Version(x => x.Version);

When I save the object, the Version property gets incremented in the database as I would expect, but the value of the property on the object only seems to change sometimes.

using (var tx = session.BeginTransaction())
{
    session.Merge(item);
    tx.Commit();

    item.Version;  // Sometimes this is still 1, when I expect it to be 2.
}

The problem is then that if it remains as 1 and I make more changes and save again I get a StaleObjectStateException.

What's weird is that sometimes it works fine and the item.Version value does get correctly incremented, but I can't figure out the difference between the cases where it does and the cases where it doesn't.

I've tried searching but can't seem to find any documentation on this. Can anyone explain what NHibernates expected behaviour is with the Version mapping开发者_Go百科?

[NHibernate version 2.1.2]

From the ISession.Merge documentation:

Copy the state of the given object onto the persistent object with the same identifier. If there is no persistent instance currently associated with the session, it will be loaded. Return the persistent instance. If the given instance is unsaved, save a copy of and return it as a newly persistent instance. The given instance does not become associated with the session.

So, it will not modify item.

(I might add I have never used Merge in my apps. You might want to review how you are dealing with attached and detached entities)

Did you try

item = session.Merge(item);
tx.Commit();

?

You need to flush the session before the updated version will propagate up to your entities. Unless you flush the session, you are responsible for keeping the entities up to date yourself.

You should TYPICALLY let the session flush on its own when its closed. However, in some instances where you rely on database updates that happen via nhibernate and not settings you make to the entity itself, you might need to flush the session yourself after a commit. In this case be aware that when you flush the session ANY entities that are dirty will be committed. This may not be desirable so be sure that the scope is very limited.