Upgrading to NH3 from NH2.1.2
We have recently update to NHibernate 3 in one of our projects. While testing I was suddenly seeing some weird UPDATE statements in NHprof.
It seemed like the NHibernate IsDirty detection had changed.
After some digging it turned out that our mapping files (made in FluentNhibernate) actually contained some minor errors when compared to the DB schema. Minor errors like value typed properties not being nullable when the ClassMap said it should be.
Debugging of NHibernate projects
I found that inserting the following into the classmaps made debugging a lot easier:
DynamicUpdate();
Now only the properties that are Dirty (according to NHibernate) are used in the SQL UPDATE statement. Here are the description from NHibernate docs:
- dynamic-update (optional, defaults to false): Specifies that UPDATE SQL should be generated at runtime and contain only those columns whose values have changed.
- dynamic-insert: (optional, defaults to false): Specifies that INSERT SQL should be generated at runtime and contain only the columns whose values are not null.
That led me directly to the property in the mapping files that had errors in it, and I could easily fix it.
Conclusion
So, in our case, it wasn’t really the NHibernate dirty detection that changed, NHibernate 3 is just not as fault tolerant, than that of NH2. So the upgrade made us discover some errors that should be corrected.
As such, this is a good thing, but it would have been nicer if NH2 had made us aware of these errors in the first place.
But hey, better late than never 
