Hibernate继承映射的简单示例

1. 继承关系：

基类：Shape

子类：Circle，Rectangle均继承Shape

package com.huey.entity;/** * 图形实体 * @author Huey2672 * */public class Shape {private Integer id;private String color;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public Shape() {}public Shape(String color) {super();this.color = color;}}

package com.huey.entity;/** * 圆形实体 * @author Huey2672 * */public class Circle extends Shape {private Double radius;public Double getRadius() {return radius;}public void setRadius(Double radius) {this.radius = radius;}public Circle() {super();}public Circle(String color, Double radius) {super(color);this.radius = radius;}}

package com.huey.entity;/** * 矩形实体 * @author Huey2672 * */public class Rectangle extends Shape {private Double length;private Double width;public Double getLength() {return length;}public void setLength(Double length) {this.length = length;}public Double getWidth() {return width;}public void setWidth(Double width) {this.width = width;}public Rectangle() {super();}public Rectangle(String color, Double length, Double width) {super(color);this.length = length;this.width = width;}}

2.  TPH(Table Per Hierarchy)映射策略，每棵继承树使用一张表，Shape.hbm.xml：

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.huey.entity"><!-- 映射持久化类Shape，discriminator-value指定辨别者列值 --><class name="Shape" table="tab_shape" discriminator-value="Shape"><id name="id" column="shape_id"><generator class="increment"></generator></id><!-- 指定映射辨别者列，其类型指定为string --><discriminator column="type" type="string"/><property name="color" column="color"/><!-- subclass映射子持久化类Circle，discriminator-value指定辨别者列值 --><subclass name="Circle" discriminator-value="Circle"><property name="radius" column="radius"/></subclass><!-- subclass映射子持久化类Rectangle，discriminator-value指定辨别者列值 --><subclass name="Rectangle" discriminator-value="Rectangle"><property name="length" column="length"/><property name="width" column="width"/></subclass></class></hibernate-mapping>

数据表结构：

tab_shape

 SHAPE_IDTYPECOLORRADIUSLENGTHWIDTH11CircleRed2(null)(null)22RectangleBlue(null)2.53.533ShapeGreen(null)(null)(null)

3. TPS(Table Per Subclass)映射策略，每个子类都有一张表，Shape.hbm.xml：

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.huey.entity"><!-- 映射持久化类Shape --><class name="Shape" table="tab_shape"><id name="id" column="shape_id"><generator class="increment"></generator></id><property name="color" column="color"/><!-- joined-subclass映射子持久化类Circle --><joined-subclass name="Circle" table="tab_circle"><!-- 必须使用key元素映射父子类的共有主键 --><key column="circle_id"/><property name="radius" column="radius"/></joined-subclass><!-- joined-subclass映射子持久化类Rectangle --><joined-subclass name="Rectangle" table="tab_rect"><key column="rect_id"/><property name="length" column="length"/><property name="width" column="width"/></joined-subclass></class></hibernate-mapping>

数据表结构：

tab_shape

 SHAPE_IDCOLOR11Red22Blue33Greentab_circle

 CIRCLE_IDRADIUS112.0tab_rect

 RECT_IDLENGTHWIDTH123.53.5
4. TPC(Table Per Concrete Class)映射策略，每个具体类使用一张表，Shape.hbm.xml：

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.huey.entity"><!-- 映射持久化类Shape --><class name="Shape" table="tab_shape"><id name="id" column="shape_id"><generator class="increment"></generator></id><property name="color" column="color"/><!-- union-subclass映射子持久化类Circle --><union-subclass name="Circle" table="tab_circle"><property name="radius" column="radius"/></union-subclass><!-- union-subclass映射子持久化类Rectangle --><union-subclass name="Rectangle" table="tab_rect"><property name="length" column="length"/><property name="width" column="width"/></union-subclass></class></hibernate-mapping>

数据表结构：

tab_shape

 SHAPE_IDCOLOR13Greentab_circle

 SHAPE_IDCOLORRADIUS11Red2.0tab_rect

 SHAPE_IDCOLORLENGTHWIDTH12Blue2.53.5

5. 如果基类是抽象类的话，在class元素中，将abstract属性值设置为true：<class name="Shape" table="tab_shape" abstract="true">...</class>，这样，在TPC映射策略中，将不必使用数据表tab_shape。