分三種

1.單表繼承

既然是單表繼承就需要一個鍵值來標識類別

class以discriminator-value來標識類別

discriminator 用以表示鑒別器的表字段

繼承的類以subclass來標識

以extends來標識繼承的類

(1)父類

<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)子類

<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)生成的數據庫測試數據

看圖更能理解意圖

2.鑒別器

這里看一下鑒別器的使用,可以指定鑒別器的值,以辨別不同的類,如下:

多個類映射到同張表,Foo 類以Green標識,Baz 則具備了Color 屬性,Foo可以說是Baz的特殊類別,都是通過配置文件來實現

<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>
測試數據

3.每個子類一張表(具備與父類有關聯關系的)

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>

生成表結構

?

4.無關聯關系的繼承表

即每張表都會生成父類的字段

<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>
數據庫表結構

轉載于:https://www.cnblogs.com/Clingingboy/archive/2009/08/02/1536971.html

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