The instantiation mode can be configured globally or on a per class basis.
.NET: Db4oFactory.Configure().CallConstructors(true)
This will configure db4o to use constructors to reinstantiate any object from the database. (The default is false).
.NET: Db4o.Configure().ObjectClass(TypeOf(Foo)).CallConstructor(true)
This will configure db4o to use constructor calls for this class and all its subclasses.