继承映射
对象模型(Java类结构)
一个类继承体系一张表(subclass)(表结构)
1、一个类继承体系一张表(subclass)(映射文件)
<class name="Employee" table="employee" discriminator-value="0">
<id name="id">
<generator class="native"/>
</id>
<discriminator column="type" type="int"/>
<property name="name"/>
<many-to-one name=”depart” column=”depart_id”/>
<subclass name="Skiller" discriminator-value="1">
<property name=”skill”/>
</subclass>
<subclass name="Sales" discriminator-value="2">
<property name="sell"/>
</subclass>
</class>
实例代码：
package com.dzq.domain;
import java.io.Serializable;
public class Employee implements Serializable{
private int id;
private String name;
private Department depart;
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 Department getDepart() {
return depart;
}
public void setDepart(Department depart) {
this.depart = depart;
}
}
子类：
package com.dzq.domain;
public class Sales extends Employee {
private int sell;
public int getSell() {
return sell;
}
public void setSell(int sell) {
this.sell = sell;
}
}
package com.dzq.domain;
public class Skiller extends Employee {
private String skiller;
public String getSkiller() {
return skiller;
}
public void setSkiller(String skiller) {
this.skiller = skiller;
}
}
映射关系：
<?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 package="com.dzq.domain"> <class name="Employee" table="employee" discriminator-value="0">
<id name="id" column="id">
<generator class="native" />
</id>
<discriminator column="type"/>
<property name="name" column="name" />
<many-to-one name="depart" column="depart_id" />
<subclass name="Skiller" discriminator-value="1">
<property name="skiller"/>
</subclass>
<subclass name="Sales" discriminator-value="2">
<property name="sell"/>
</subclass>
</class> </hibernate-mapping>
测试代码：
package com.dzq.test; import java.util.HashSet;
import java.util.Set; import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction; import com.dzq.domain.Department;
import com.dzq.domain.Employee;
import com.dzq.domain.Sales;
import com.dzq.domain.Skiller;
import com.dzq.utils.HibernateUntils; public class ManyToOne { public static void main(String[] args) {
add();
query(2);
}
public static void addEmAndDe(){
Employee em=new Employee();
Department depart=new Department();
depart.setName("FBI");
em.setDepart(depart);
em.setName("AK47");
HibernateUntils.add(depart);
HibernateUntils.add(em);
} public static void add(){
Session s=null;
Transaction ts=null;
try { Department dep=new Department();
dep.setName("FBI");
Employee e1=new Employee();
Skiller e2=new Skiller();
Sales e3=new Sales();
e1.setName("hi");
e1.setDepart(dep);
e2.setName("hello");
e2.setDepart(dep);
e2.setSkiller("skill");
e3.setName("fuck");
e3.setDepart(dep);
e3.setSell(100);
Set<Employee> empls=new HashSet<Employee>();
empls.add(e1);
empls.add(e2);
empls.add(e3);
dep.setEmpls(empls);
s=HibernateUntils.getSession();
ts=s.beginTransaction();
s.save(dep);
s.save(e1);
s.save(e2);
s.save(e3); ts.commit();
} catch (Exception e) {
ts.rollback();
throw new RuntimeException(e);
}finally{
if(s!=null){
s.close();
}
}
} public static Employee query(int id){
Session s=null;
try{
s=HibernateUntils.getSession();
Employee emp=(Employee) s.get(Employee.class, id);
//Hibernate.initialize(emp.getDepart());
System.out.println(emp.getClass());
return emp;
}finally{
if(s!=null){
s.close();
}
}
} }
表结构
2、每个子类一张表(joined-subclass) (表结构)
每个子类一张表(joined-subclass) (映射文件)
<class name="Employee" table="employee">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<joined-subclass name="Skiller" table="skiller">
<key column="employee_id"/>
<property name="skill"/>
</joined-subclass>
<joined-subclass name="Sales" table="sales">
<key column="employee_id"/>
<property name="sell"/>
</joined-subclass>
</class>
3、混合使用“一个类继承体系一张表”和“每个子类一张表” (表结构)
混合使用“一个类继承体系一张表”和“每个子类一张表” (映射文件)
<class name="Employee" table="employee">
<id name="id">
<generator class="native"/>
</id>
<discriminator column="type"/>
<property name="name"/>
<subclass name="Skiller">
<property name="net"/>
</subclass>
<subclass name=”Sales”">
<join table="sales">
<key column="employee_id"/>
<property name="sell"/>
</join>
</subclass>
</class>
数据库结构：
4、每个具体类一张表(union-subclass) (表结构)
每个具体类一张表(union-subclass) (映射文件)
<class name="Employee" abstract="true">
<id name="id">
<generator class="hilo"/>
</id>
<property name="name"/>
<union-subclass name="Skiller" table="skiller">
<property name="skill"/>
</union-subclass>
<union-subclass name="Sales" table="sales">
<property name="sell"/>
</union-subclass>
</class>
主健不能是identity类型，如果父类是abstract=”true”就不会有表与之对应。
隐式多态，映射文件没有联系，限制比较多很少使用。