A co-worker of mine, Brian Kapellusch, is working on a web framework to give us a garden path for ASP.NET applications. The code that he's writing (and the code to use it) is trés elegant. One of the underpinnings of this framework is his use of the ObjectDataSource class (ODS). I am making heavy use of NHibernate and Spring.NET in this application as well. My understanding of the ODS told me that if I wanted to control how the source object was created, that I simply needed to handle the ObejctCreating event and assign the desired object instance in that event to e.ObjectInstance (see here for some more usage examples).

However, it turns out that is not enough to fully control when an object gets created. If you set the TypeName property to a concrete class, ODS will also create a new object behind the scenes - even if you have handled the ObjectCreating event. This becomes very problematic when using an IoC container to automatically build up and inject properties into your class.

The bottom line is this: If you see one version of your object that has things built up properly (because the IoC container was used properly), and one version that has null properties (because, in essence, ODS called "new MyClass()" for you, which doesn't let the IoC container do it's job), you should change the TypeName to point to the interface type instead of the concrete class type. Much thanks to Brian for this one.