LINQ to Entites: How and where to use OnPropertyChanging or ReportPropertyChanging events?

I'm trying to determine when a certain field is updated, and perform an action when the field changes.

I'm using a custom binder for the class, and the first call in the binder is to base.BindModel(), at which point the original value is gone. When do the OnPropertyChanging and ReportPropertyChanging events get called? Is there any w开发者_如何转开发ay to use these from my binder?