自定义类中linq to sql的deleteonnull(关联属性)?

是否可以在自定义类上添加“deleteonnull=true”,而不是直接修改dbml(generated)类?

例如,假设这是我生成的DBML类的一部分:

[Table(Name="OrderDetails")]
public partial class OrderDetail : 
       INotifyPropertyChanging, INotifyPropertyChanged
{
    // deleted for brevity

    [Association(Name="Order_OrderDetail", 
         Storage="_Order", ThisKey="OrderId", 
         OtherKey="OrderId", IsForeignKey=true, DeleteOnNull=true)]
    public Order Order 
    {
        get { /* deleted */ }
        set { /* deleted */ }
    }
}

那么,是否可以将“deleteonnull=true”放在单独的类上?是吗?怎样?我没有任何运气就尝试了以下方法:

[MetadataType(typeof(OrderDetailMetadata))]
public partial class OrderDetail {
    internal sealed class OrderDetailMetadata
    {
        [Association(DeleteOnNull = true)]
        public object Order;
    }
}