NHibernate Step By Step(2)-继承映射

分三种

1.单表继承

既然是单表继承就需要一个键值来标识类别

1. class以discriminator-value来标识类别
2. discriminator 用以表示鉴别器的表字段
3. 继承的类以subclass来标识
4. 以extends来标识继承的类

(1)父类

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false">
<class
name="NHibernate.Test.Subclass.SubclassBase, NHibernate.Test"
table="one_tab"
discriminator-value="SUPER" 
>
<id
name="Id"
type="Int32"
unsaved-value="0"
column="joined_subclass_id"
access="nosetter.camelcase-underscore"
>
<generator class="native" />
</id>
<discriminator column="disc_column" type="String" />
<property name="TestLong" column="test_long" type="Int64" />
<property name="TestString" column="test_string" type="String" />
<property name="TestDateTime" column="test_date_time" type="DateTime" />
</class>
</hibernate-mapping>

(2)子类

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false">
<subclass
extends="NHibernate.Test.Subclass.SubclassBase, NHibernate.Test"
name="NHibernate.Test.Subclass.SubclassOne, NHibernate.Test"
discriminator-value="SUB"
>
<property name="OneTestLong" column="one_test_long" type="Int64" />
</subclass>
</hibernate-mapping>

(3)生成的数据库测试数据

看图更能理解意图

2.鉴别器

这里看一下鉴别器的使用,可以指定鉴别器的值,以辨别不同的类,如下:

多个类映射到同张表,Foo 类以Green标识,Baz 则具备了Color 属性,Foo可以说是Baz的特殊类别,都是通过配置文件来实现

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false" namespace="NHibernate.Test.Subclass.EnumDiscriminator" assembly="NHibernate.Test">
<class name="Foo" table="subclass_enumdiscriminator" discriminator-value="Green">
<id name="Id" type="Int64">
<generator class="assigned"/>
</id>
<discriminator column="Color" type="NHibernate.Test.Subclass.EnumDiscriminator.Colors, NHibernate.Test"/>
<subclass name="Bar" discriminator-value="Blue"/>
</class>
<class name="Baz" table="subclass_enumdiscriminator">
<id name="Id" type="Int64">
<generator class="assigned"/>
</id>
<property name="Color"/>
</class>
</hibernate-mapping>

测试数据

3.每个子类一张表(具备与父类有关联关系的)

映射文件

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false">
<class name="NHibernate.Test.JoinedSubclass.Person, NHibernate.Test" table="person" proxy="NHibernate.Test.JoinedSubclass.Person, NHibernate.Test">
<id name="Id" type="Int32" unsaved-value="0" column="person_id" access="nosetter.camelcase-underscore">
<generator class="native"/>
</id>
<property name="Name" column="name"/>
<property name="Sex" column="sex"/>
<component name="Address">
<property name="Street"/>
<property name="Zip"/>
<property name="Country"/>
</component>
<joined-subclass name="NHibernate.Test.JoinedSubclass.Employee, NHibernate.Test" table="empl" proxy="NHibernate.Test.JoinedSubclass.Employee, NHibernate.Test">
<key column="person_id"/>
<property name="Title" not-null="true" length="20"/>
<property name="Salary" type="Decimal(19,5)"/>
<many-to-one name="Manager"/>
</joined-subclass>
<joined-subclass name="NHibernate.Test.JoinedSubclass.Customer, NHibernate.Test" table="cust" proxy="NHibernate.Test.JoinedSubclass.Customer, NHibernate.Test">
<key column="person_id"/>
<property name="Comments"/>
<many-to-one name="Salesperson"/>
</joined-subclass>
</class>
</hibernate-mapping>

生成表结构

 

4.无关联关系的继承表

即每张表都会生成父类的字段

<class name="Person" table="UPerson">
<id name="id"
column="person_id"
unsaved-value="0">
<generator class="hilo"/>
</id>
<property name="name"
unique-key="NameUniqueKey"
not-null="true"
length="80"/>
<property name="sex"
not-null="true"
update="false"/>
<component name="address">
<property name="address" index="AddressIndex"/>
<property name="zip" index="AddressIndex"/>
<property name="country"/>
</component>
<union-subclass name="Employee" table="UEmployee">
<property name="title"
not-null="true"
length="20"/>
<property name="salary" />
<many-to-one name="manager"/>
</union-subclass>
<union-subclass name="Customer" table="UCustomer">
<property name="comments"/>
<many-to-one name="salesperson"/>
</union-subclass>
</class>

数据库表结构