hibernate继承实现
http://www.blogjava.net/xiaodu/archive/2008/07/11/214188.html
hiberate继承分为三种方式:一个表对应所有继承的类,具体类对应一个表,一个类对应一个表(父类及子类)
一个类对应一个表(父类及子类)
数据库脚本
CREATE TABLE `t_item1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`manufacture` varchar(20) DEFAULT NULL,
`name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=DYNAMIC
CREATE TABLE `t_book1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`manufacture` varchar(20) DEFAULT NULL,
`pagecount` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=DYNAMIC COMMENT='InnoDB free: 3072 kB'
CREATE TABLE `t_dvd1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`manufacture` varchar(20) DEFAULT NULL,
`regioncode` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=DYNAMIC
类代码
public class TItem1 implements Serializable {
private int id;
private String name;
private String manufacture;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getManufacture() {
return manufacture;
}
public void setManufacture(String manufacture) {
this.manufacture = manufacture;
}
}
public class TBook1 extends TItem1 implements Serializable {
private int pagecount;
public int getPagecount() {
return pagecount;
}
public void setPagecount(int pagecount) {
this.pagecount = pagecount;
}
}
public class TDvd1 extends TItem1 implements Serializable {
private String regioncode;
public String getRegioncode() {
return regioncode;
}
public void setRegioncode(String regioncode) {
this.regioncode = regioncode;
}
}
配置文件
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="mypackage.TItem1" table="t_item1">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
<property name="manufacture" column="manufacture"/>
<joined-subclass name="mypackage.TBook1" table="t_book1">
<key column="id"/>
<property name="pagecount" column="pagecount" type="java.lang.Integer"/>
</joined-subclass>
<joined-subclass name="mypackage.TDvd1" table="t_dvd1">
<key column="id"/>
<property name="regioncode" column="regioncode" type="java.lang.String"/>
</joined-subclass>
</class>
</hibernate-mapping>
具体类对应一个表
数据库脚本
CREATE TABLE `t_book2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`manufacture` varchar(20) DEFAULT NULL,
`pagecount` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=17 DEFAULT CHARSET=latin1
CREATE TABLE `t_dvd2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(23) DEFAULT NULL,
`manufacture` varchar(20) DEFAULT NULL,
`regioncode` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=18 DEFAULT CHARSET=latin1
类代码
public abstract class TItem2 implements java.io.Serializable {
private int id;
private String name;
private String manufacture;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getManufacture() {
return manufacture;
}
public void setManufacture(String manufacture) {
this.manufacture = manufacture;
}
}
public class TDvd2 extends TItem2 implements Serializable {
private String regioncode;
public String getRegioncode() {
return regioncode;
}
public void setRegioncode(String regioncode) {
this.regioncode = regioncode;
}
}
public class TBook2 extends TItem2 implements Serializable {
private int pagecount;
public int getPagecount() {
return pagecount;
}
public void setPagecount(int pagecount) {
this.pagecount = pagecount;
}
}
配置文件
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="mypackage.TDvd2" table="t_dvd2">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
<property name="manufacture" column="manufacture"/>
<property name="regioncode" column="regioncode"/>
</class>
<class name="mypackage.TBook2" table="t_book2">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
<property name="manufacture" column="manufacture"/>
<property name="pagecount" column="pagecount"/>
</class>
</hibernate-mapping>
一个表对应所有继承的类
数据库脚本
CREATE TABLE `t_item3` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`manufacture` varchar(20) DEFAULT NULL,
`pagecount` int(11) DEFAULT NULL,
`regioncode` varchar(20) DEFAULT NULL,
`category` varchar(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1
类代码
public class TItem3 implements Serializable {
private int id;
private String name;
private String manufacture;
private String category;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getManufacture() {
return manufacture;
}
public void setManufacture(String manufacture) {
this.manufacture = manufacture;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
}
public class TDvd3 extends TItem3 implements Serializable {
private String regioncode;
public String getRegioncode() {
return regioncode;
}
public void setRegioncode(String regioncode) {
this.regioncode = regioncode;
}
}
public class TBook3 extends TItem3 implements Serializable {
private int pagecount;
public int getPagecount() {
return pagecount;
}
public void setPagecount(int pagecount) {
this.pagecount = pagecount;
}
}
配置文件
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="mypackage.TItem3" table="t_item3">
<id name="id" column="id">
<generator class="identity"/>
</id>
<discriminator column="category" type="java.lang.String"/>
<property name="name" column="name"/>
<property name="manufacture" column="manufacture"/>
<subclass name="mypackage.TDvd3" discriminator-value="1">
<property name="regioncode" column="regioncode"/>
</subclass>
<subclass name="mypackage.TBook3" discriminator-value="0">
<property name="pagecount" column="pagecount"/>
</subclass>
</class>
</hibernate-mapping>
三种方式的优缺点
每个类对应一个表
缺点:创建表过多,查询需用求外连接,优点:某个表字段发生变化只需修改相对表,支持多态查询,符合关系型数据库设计
具体类对应一个表
缺点:数据表包含重复字段,如果父类发生变化子类也要变化,查询父类时要查询所有子类,不支持多态查询,优点:符合关系型数据库设计
一个表对应所有类
缺点:表中引入区分子类的字段,子类的字段不能创建为空,优点:只需一张表,有很好的查询性能,只要修改一张表,支持多态查询
