我有一个像这样定义的类:
public class StateMachineMetadata<T> where T: struct
{
public virtual int ID { get; protected set; }
public virtual T State { get; set; }
public virtual DateTime DateChanged { get; set; }
}
State
属性是枚举的地方:
public enum CarState
{
Stopped = 1,
Moving = 2
}
public enum OrderState
{
Ordered = 1,
Delivered = 2
}
我可以有两种类型:
StateMachineMetadata<CarState>, StateMachineMetadata<OrderState>
使用NHibernate在一个表StateMachineMetadata
中保留?
=== update ===
由于变通方法通用部分可以移动到界面:
public interface IStateMachineMetadata<T> where T: struct
{
int ID { get; }
T State { get; set; }
DateTime DateChanged { get; set; }
}
public class StateMachineMetadataBase
{
public virtual int ID { get; protected set; }
public virtual DateTime DateChanged { get; set; }
}
public class CarStateMachineMetadata
: StateMachineMetadataBase, IStateMachineMetadata<CarState>
{
public virtual CarState State { get; set; }
}
答案 0 :(得分:3)
否,这就是原因。
假设我们在StateMachineMetadata
表中有两行:
ID | State | DateChanged
1 | 1 | 2012-02-13
2 | 1 | 2012-02-14
如果State
列同时映射到CarState
和OrderState
,NHibernate将如何确定要反序列化的枚举?一种解决方案是将一个鉴别器列添加到StateMachineMetadata
表中,该表告诉NHibernate它应该将特定行映射到哪个类型。
例如Type
鉴别器列:
ID | State | DateChanged | Type
1 | 1 | 2012-02-13 1
2 | 1 | 2012-02-14 2
告诉NHibernate第一行代表StateMachineMetadata<CarState>
而第二行代表StateMachineMetadata<OrderState>
。这在NHibernate中称为Table per class hierarchy mapping。它要求两个类都从公共基类继承,在您的情况下,它基本上是StateMachineMetadata<T>
。
但是这里的捕捉:NHibernate 没有办法用开放的泛型类型映射一个类。原因是it's simply not possible。
然而,NHibernate 确实允许您使用封闭的泛型来映射类。您无法将它们映射到同一个表。以下是这种配置的样子:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="MyAssembly"
namespace="MyNamespace">
<class name="StateMachineMetadata`1[MyNamespace.CarState]"
table="StateMachineMetadata_CarState">
<!-- property to column mappings -->
</class>
<class name="StateMachineMetadata`1[MyNamespace.OrderState]"
table="StateMachineMetadata_OrderState">
<!-- property to column mappings -->
</class>
</hibernate-mapping>