hiberate繼承分為三種方式:一個表對應所有繼承的類,具體類對應一個表,一個類對應一個表(父類及子類)
一個類對應一個表(父類及子類)
數據庫腳本
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
類代碼
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>
具體類對應一個表
數據庫腳本
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
類代碼
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>
一個表對應所有繼承的類
數據庫腳本
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
類代碼
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>
三種方式的優缺點
每個類對應一個表
缺點:創建表過多,查詢需用求外連接,優點:某個表字段發生變化只需修改相對表,支持多態查詢,符合關系型數據庫設計
具體類對應一個表
缺點:數據表包含重復字段,如果父類發生變化子類也要變化,查詢父類時要查詢所有子類,不支持多態查詢,優點:符合關系型數據庫設計
一個表對應所有類
缺點:表中引入區分子類的字段,子類的字段不能創建為空,優點:只需一張表,有很好的查詢性能,只要修改一張表,支持多態查詢