Hibernate继承映射

最新推荐文章于 2024-07-26 15:36:29 发布

最新推荐文章于 2024-07-26 15:36:29 发布 · 118 阅读

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本文介绍了三种将继承关系映射到数据库表的方法：继承关系层次一个表、每个具体类一个表及每个子类一个表，并提供了具体的代码示例。

继承映射

3种方式，继承关系映射到数据库的表中

1.继承关系层次一个表(Table per class hierarchy)，这种方式使用一个表存储同一个继

承层次的所有类，使用额外的字段来表示所记录的是哪一个子类的数据。
2.每一个具体类一个表(Table per concrete class),这种方式让继承关系中的每个具体类

对应一个表
3.每个子类一个表(Table per subclass),这种方式让继承关系中的父类和每一个子类分别

对应一个表，父类与子类对应的表通过外键产生关联

继承关系层次一个表

public class Delivery implements java.io.Serializable{
	private Integer id;
	private String recipient;
	private String phone;
	private String address;
	private String postcode;
}

public class PostDelivery extends Delivery{
	private String parcelNumber;
}

public class ExpressDelivery extends Delivery{
	private String expressCompany;
	private String expressNumber;
}

并且生成getter和setter方法
在delivery.hbm.xml修改
在id 下面加入

<!--以delivery_type区分-->
<discriminator column="delivery_type"></discriminator> 

<!--子类PostDelivery特有的属性-->
<subclass name="com.rbh.examples.PostDelivery" discriminator-value="Post">
        <property name="paracelNumber" type="java.lang.String">
            <column name="PARACEL_NUMBER" length="30" />
        </property>
        </subclass>

<!--子类ExpressDelivery特有的属性-->
<subclass name="com.rbh.examples.ExpressDelivery" discriminator-

value="Express">
        <property name="expressNumber" type="java.lang.String">
            <column name="EXPRESS_NUMBER" length="30" />
        </property>
        <property name="expressCompany" type="java.lang.String">
            <column name="EXPRESS_COMPANY" length="30" />
        </property>
        </subclass>

每个具体类一个表

public abstract class Delivery implements java.io.Serializable
{
	private Integer id;
	private String recipient;
	private String phone;
	private String address;
	private String postcode;
}

<class name="com.rbh.examples.Delivery" table="DELIVERY" schema="SCOTT" 

abstract="true"> 为抽象类

  <union-subclass name="com.rbh.examples.PostDelivery" table="post_delivery">
        <property name="parcelNumber" type="java.lang.String">
            <column name="PARCEL_NUMBER" length="30" />
        </property>
        </union-subclass>

<union-subclass name="com.rbh.examples.ExpressDelivery" 

table="express_delivery">
        <property name="expressNumber" type="java.lang.String">
            <column name="EXPRESS_NUMBER" length="30" />
        </property>
        <property name="expressCompany" type="java.lang.String">
            <column name="EXPRESS_COMPANY" length="30" />
        </property>
        </union-subclass>

每个子类一个表

public class Delivery implements java.io.Serializable{
	private Integer id;
	private String recipient;
	private String phone;
	private String address;
	private String postcode;
}

public class PostDelivery extends Delivery{
	private String parcelNumber;
}

public class ExpressDelivery extends Delivery{
	private String expressCompany;
	private String expressNumber;
}

<joined-subclass name="com.rbh.examples.PostDelivery" table="post_delivery">
        <key column="id" foreign-key="id"></key>
        <property name="parcelNumber" type="java.lang.String">
            <column name="PARCEL_NUMBER" length="30" />
        </property>
        </joined-subclass>

<joined-subclass name="com.rbh.examples.ExpressDelivery" 

table="express_delivery">
        <key column="id" foreign-key="id"></key>
        <property name="expressNumber" type="java.lang.String">
            <column name="EXPRESS_NUMBER" length="30" />
        </property>
        <property name="expressCompany" type="java.lang.String">
            <column name="EXPRESS_COMPANY" length="30" />
        </property>
        </joined-subclass>