Question

I have an object hierarchy as follows:

• Object
  • Reports
    • Report Items

Based on other posts here, I set the Report.ReportItems mapping to Inverse, and CascadeAllDeleteOrphan. This makes it so when I remove a Report from an Object it goes to erase the ReportItems in that report.

The way it does it is very inefficient. It basically does a Delete ... Where ReportItemID = ?.

I’ve seen suggestions to increase the batch size to prevent this from being done in too many round trips, but that seems like a sloppy fix. Is there a way to make NHibernate generate a query like this instead:

Delete ... Where ReportID = ?

This way it would execute one query that would delete all the ReportItems instead of one statement per ReportItem.

Thanks in advance.

Edit

I have heard from a few people that NHibernate will simply not work this way with standard QueryOver etc.

I decided to start using HQL to fix the problem. I will later use some reflection to make sure there are no “magic strings” being used.

I had the idea to:

1. Use HQL to mass-delete the Report Items
2. Tell the Session to Refresh the object so it could detect that the Report Items are gone
3. Then tell the session to erase the Report, and let it clean up the remaining information

This does not work though. You can see the code below:

Session.CreateQuery("delete ReportItem r where r.Report= :report").SetEntity("report", SelectedReport).ExecuteUpdate()
Session.Refresh(SelectedReport)
Object.Reports.Remove(SelectedReport)
Session.Delete(SelectedReport)
Session.Update(Object)

I have also tried doing a Session.Evict after performing the HQL statements, but NHibernate keeps using the cache to try to delete the ReportItems. Any tips on how to do this?

Answer 1

After a lot of research I have found that this is simply not possible. You can use HQL, raw SQL statements, or rely on database rules to perform the deletes by enforcing a relationship. However, there is no way to tell NHibernate to delete a list of objects based on their owner’s ID.