20160509-hibernate--继承映射

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。