Remove deleted items from first level cache in NHibernate? Or: how to check if cached items have been deleted?

Question

We have a brownfield multi-user application (99% Delphi, 1% .net) which uses NHibernate for the persistency of the .net modules. In my application I can add categories to some entity. If I select one and decide to not use it (thus removing the category again) I has been loaded by NHibernate and will stay in the session's first level cache. Now, if some other user deletes this category and I try to save my entity my application throws an exception because the object loaded doesn't exist anymore.

my question: is there a way to check if my cache has items loaded which don't exist anymore? and if so, is there a way to remove non-exist entities from my cache?

So what happens: I load an entity (added to session cache) I add a category (added to session cache) Someone else deletes the category from the database. I save my entity and the exception occurs because the category doesn't exist anymore.

It's still in the session cache. It would be nice if I could (automatically) remove it from my session's cache? is there a way to clean up the cache and remove objects that don't exist anymore?

Regards, Ted

Answer 1

There's no option in NHibernate to do it automatically, at least not with ISession. You could use IStatelessSession for loading, since it doesn't have first-level cache, but you'll lose many other features that ISession provides.

You could also call ISession.Clear() to clear the session (first-level) cache, or ISession.Evict() to evict certain entities from session, but that's not automatic.

How long do you keep your session object? Maybe you need a different session management context.

If the lifespan of your session is shorter, you can still achieve entity caching, but with second-level cache. SysCache2 is one of second-level cache providers that has a support for SqlCacheDependency. This means that you could set cache expiration when some objects in database change.