NHibernate：具有通用枚举属性的映射类

我有一个这样定义的类：

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; }
}

如果国家财产是枚举：

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保留在一个表StateMachineMetadata中？

===更新===

解决方法通用部分可以移至接口：

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; }
}

解决方法:

不,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将如何确定反序列化到的枚举？一种解决方案是在StateMachineMetadata表中添加一个鉴别符列,该列告诉NHibernate它应该将特定行映射到哪种类型.
例如类型鉴别符列：

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>.而第二个是StateMachineMetadata< OrderState>.这在NHibernate中称为Table per class hierarchy mapping.它要求两个类都从一个公共基类继承,在您的情况下,该基类自然是StateMachineMetadata T.

但是这里有个问题：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.

但是,NHibernate确实允许您使用封闭的泛型映射类.您只是不能将它们映射到同一张表.这样的配置如下所示：

<?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>

标签：enums,nhibernate,nhibernate-mapping,c,net
来源： https://codeday.me/bug/20191201/2083043.html