NH Prof new featureSuperfluous
Yes, I am aware that I said that I would only have two more feature for NH Prof before releasing. But I am currently being held hostage by the new features fairy, and negotiations over a feature freeze seems to have gotten to a stand still. Beside, it is a neat feature.
The actual feature is quite simple. Let us say that we have the following model:
Notice that this is a very common case of bidirectional association, and this is mapped to the following table model:
Notice that while on the object model this is a bidirectional association and is maintained by two different places, it is maintained on a single place in the database.
This is a a very common case, and quite a few people get it wrong. By default, NHibernate has to assume that it must update the column on both sides, so creating a new post and adding it to the Blog’s Posts collection will result in two statements being written to the database:
As you can see, we are actually setting the BlogId to the same value, twice.
Now, there is a very easy fix for this issue, all you have to do is to tell NHibernate on the Blog’s Posts mapping that this is a collection where the responsibility for actually updating the column value is on the other side. This is also something that I tend to check in code reviews quite often. The fix is literally just specifying inverse=’true’ on the <many-to-one> association.
And now NH Prof will detect and warn about such cased:
This is also the first case in which I am starting to do much more in depth analysis of what is actually going on with NHibernate. I planned to do this sort of thing after the v1.0 release, but as I said, I am held hostage by the new features fairy, and this is my negotiation technique :-)
More posts in "NH Prof new feature" series:
- (09 Dec 2010) Alert on bad ‘like’ query
- (10 Dec 2009) Filter static files
- (16 Nov 2009) Exporting Reports
- (08 Oct 2009) NHibernate Search Integration
- (19 Aug 2009) Multiple Session Factory Support
- (07 Aug 2009) Diffing Sessions
- (06 Aug 2009) Capturing DDL
- (05 Aug 2009) Detect Cross Thread Session Usage
- (22 May 2009) Detecting 2nd cache collection loads
- (15 May 2009) Error Detection
- (12 May 2009) Queries by Url
- (04 Feb 2009) View Query Results
- (18 Jan 2009) Superfluous <many-to-one> update
- (18 Jan 2009) URL tracking
- (10 Jan 2009) Detecting distributed transactions (System.Transactions)
- (06 Jan 2009) The Query Cache
- (05 Jan 2009) Query Duration
- (24 Dec 2008) Unbounded result sets
- (24 Dec 2008) Row Counts