使用 Fluent NHibernate 进行继承映射 [英] Inheritance Mapping with Fluent NHibernate

问题描述

鉴于以下场景，我想使用 Fluent NHibernate 将类型层次结构映射到数据库架构.

我使用的是 NHibernate 2.0

<小时>

类型层次结构

公共抽象类Item{公共虚拟 int ItemId { 获取；放;}公共虚拟字符串 ItemType { 获取；放;}公共虚拟字符串 FieldA { get;放;}}公共抽象类 SubItem : Item{公共虚拟字符串 FieldB { get;放;}}公共类 ConcreteItemX : SubItem{公共虚拟字符串 FieldC { get;放;}}公共类 ConcreteItemY : 项目{公共虚拟字符串 FieldD { get;放;}}

查看图片

Item 和 SubItem 类是抽象的.

<小时>

数据库架构

<前>+--------------+ +---------------+ +---------------+|项目 ||混凝土项目X ||混凝土项目Y |+==========+ +================+ +================+|商品编号 ||商品编号 ||商品编号 ||项目类型 ||场C ||领域D ||领域A |+--------------+ +--------------+|场B |+-----------+

查看图片

ItemType 字段决定了具体的类型.

ConcreteItemX表中的每条记录在Item表中都有一个对应的记录；ConcreteItemY 表也是如此.

如果项目类型为 ConcreteItemY，

FieldB 始终为 null.

<小时>

映射(到目前为止)

public class ItemMap : ClassMap{公共 ItemMap(){WithTable("项目");Id(x => x.ItemId, "ItemId");Map(x => x.FieldA, "FieldA");JoinedSubClass("ItemId", MapConcreteItemX);JoinedSubClass("ItemId", MapConcreteItemY);}private static void MapConcreteItemX(JoinedSubClassPart part){part.WithTableName("ConcreteItemX");part.Map(x => x.FieldC, "FieldC");}private static void MapConcreteItemY(JoinedSubClassPart part){part.WithTableName("ConcreteItemX");part.Map(x => x.FieldD, "FieldD");}}

FieldB 未映射.

<小时>

问题

如何使用 Fluent NHibernate 映射 SubItem 类的 FieldB 属性?

有什么方法可以使用 ItemType 字段来利用 DiscriminateSubClassesOnColumn 吗?

<小时>

附录

我能够使用 hbm.xml 文件实现所需的结果:

<id name="ItemId" type="Int32" column="ItemId"><generator class="native"/></id><discriminator column="ItemType" type="string"/><属性名称=字段A"列=字段A"/><subclass name="ConcreteItemX" discriminator-value="ConcreteItemX"><!-- 请注意此处的 FieldB 映射--><属性名称=FieldB"列=FieldB"/><join table="ConcreteItemX"><key column="ItemId"/><属性名称=FieldC"列=FieldC"/></加入></子类><subclass name="ConcreteItemY" discriminator-value="ConcreteItemY"><join table="ConcreteItemY"><key column="ItemId"/><属性名称=FieldD"列=FieldD"/></加入></子类></class>

如何使用 Fluent NHibernate 完成上述映射?

是否可以使用 Fluent NHibernate 将 table-per-class-hierarchy 与 table-per-subclass 混合使用?

解决方案

我知道这真的很旧，但现在设置 fluent 以生成您最初想要的精确映射非常简单.由于我在搜索答案时遇到了这篇文章，所以我想我会发布它.

您只需为基类创建 ClassMap，而无需引用您的子类:

public class ItemMap : ClassMap{公共 ItemMap(){this.Table("项目");this.DiscriminateSubClassesOnColumn("ItemType");this.Id(x => x.ItemId, "ItemId");this.Map(x => x.FieldA, "FieldA");}}

然后像这样映射你的抽象子类:

公共类SubItemMap:SubclassMap{公共 SubItemMap(){this.Map(x => x.FieldB);}}

然后像这样映射你的具体子类:

public class ConcreteItemXMap : SubclassMap{公共 ConcretItemXMap(){this.Join("ConcreteItemX", x =>{x.KeyColumn("ItemID");x.Map("FieldC")});}}

希望这可以帮助其他人使用 fluent 寻找这种类型的映射.

Given the following scenario, I want map the type hierarchy to the database schema using Fluent NHibernate.

I am using NHibernate 2.0

---

Type Hierarchy

public abstract class Item
{
    public virtual int ItemId { get; set; }
    public virtual string ItemType { get; set; }
    public virtual string FieldA { get; set; }
}

public abstract class SubItem : Item
{
    public virtual string FieldB { get; set; } 
}

public class ConcreteItemX : SubItem
{
    public virtual string FieldC { get; set; } 
}

public class ConcreteItemY : Item
{
    public virtual string FieldD { get; set; }
}

See image

The Item and SubItem classes are abstract.

---

Database Schema

+----------+  +---------------+  +---------------+
| Item     |  | ConcreteItemX |  | ConcreteItemY |
+==========+  +===============+  +===============+
| ItemId   |  | ItemId        |  | ItemId        |
| ItemType |  | FieldC        |  | FieldD        |
| FieldA   |  +---------------+  +---------------+
| FieldB   |
+----------+

See image

The ItemType field determines the concrete type.

Each record in the ConcreteItemX table has a single corresponding record in the Item table; likewise for the ConcreteItemY table.

FieldB is always null if the item type is ConcreteItemY.

---

The Mapping (so far)

public class ItemMap : ClassMap<Item>
{
    public ItemMap()
    {
        WithTable("Item");
        Id(x => x.ItemId, "ItemId");
        Map(x => x.FieldA, "FieldA");

        JoinedSubClass<ConcreteItemX>("ItemId", MapConcreteItemX);
        JoinedSubClass<ConcreteItemY>("ItemId", MapConcreteItemY);
    }

    private static void MapConcreteItemX(JoinedSubClassPart<ConcreteItemX> part)
    {
        part.WithTableName("ConcreteItemX");
        part.Map(x => x.FieldC, "FieldC");
    }

    private static void MapConcreteItemY(JoinedSubClassPart<ConcreteItemY> part)
    {
        part.WithTableName("ConcreteItemX");
        part.Map(x => x.FieldD, "FieldD");
    }
}

FieldB is not mapped.

---

The Question

How do I map the FieldB property of the SubItem class using Fluent NHibernate?

Is there any way I can leverage DiscriminateSubClassesOnColumn using the ItemType field?

---

Addendum

I am able to achieve the desired result using an hbm.xml file:

<class name="Item" table="Item">

  <id name="ItemId" type="Int32" column="ItemId">
    <generator class="native"/>
  </id>

  <discriminator column="ItemType" type="string"/>

  <property name="FieldA" column="FieldA"/>

  <subclass name="ConcreteItemX" discriminator-value="ConcreteItemX">
    <!-- Note the FieldB mapping here -->
    <property name="FieldB" column="FieldB"/>
    <join table="ConcreteItemX">
      <key column="ItemId"/>
      <property name="FieldC" column="FieldC"/>
    </join>
  </subclass>

  <subclass name="ConcreteItemY" discriminator-value="ConcreteItemY">
    <join table="ConcreteItemY">
      <key column="ItemId"/>
      <property name="FieldD" column="FieldD"/>
    </join>
  </subclass>

</class>

How do I accomplish the above mapping using Fluent NHibernate?

Is it possible to mix table-per-class-hierarchy with table-per-subclass using Fluent NHibernate?

解决方案

I know this is really old, but it is now pretty simple to set up fluent to generate the exact mapping you initially desired. Since I came across this post when searching for the answer, I thought I'd post it.

You just create your ClassMap for the base class without any reference to your subclasses:

public class ItemMap : ClassMap<Item>
{
    public ItemMap()
    {
        this.Table("Item");
        this.DiscriminateSubClassesOnColumn("ItemType");
        this.Id(x => x.ItemId, "ItemId");
        this.Map(x => x.FieldA, "FieldA");
    }
}

Then map your abstract subclass like this:

public class SubItemMap: SubclassMap<SubItemMap>
{
    public SubItemMap()
    {
        this.Map(x => x.FieldB);
    }
}

Then map your concrete subclasses like so:

public class ConcreteItemXMap : SubclassMap<ConcreteItemX>
{
    public ConcretItemXMap()
    {
        this.Join("ConcreteItemX", x =>
        {
            x.KeyColumn("ItemID");
            x.Map("FieldC")
        });
    }
}

Hopefully this helps somebody else looking for this type of mapping with fluent.

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