Hibernate学习（九）---【继承关系】

Hibernate学习（九）---【继承关系】

继承关系分为三种：一张表对应一整棵类继承树、一个类对应一张表、每一个具体类对应一张表。
三个java类Person、Student、Teacher，Student和Teacher继承Person类并且Student和Teacher没有任何关系
代码如下：
Person.java

package  com.zzn.hibernate.model;

public   class  Person {
     private   int  id;
     private  String name;
     private   int  age;
     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   int  getAge() {
         return  age;
    }
     public   void  setAge( int  age) {
         this .age  =  age;
    }
    
    
}    

Student.java

package  com.zzn.hibernate.model;

public   class  Student  extends  Person  {
    private String cardId;

    public String getCardId() {
        return cardId;
    }
    public void setCardId(String cardId) {
        this.cardId = cardId;
    }
}

Teacher.java

package  com.zzn.hibernate.model;

public   class  Teacher  extends  Person {
     private   int  salary;
     public   int  getSalary() {
         return  salary;
    }
     public   void  setSalary( int  salary) {
         this .salary  =  salary;
    }
}

一张表对应一整棵类继承树时
Person.hbm.xml

<? xml version="1.0" encoding='gb2312' ?>   
<! DOCTYPE hibernate-mapping PUBLIC  
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >   
     
< hibernate-mapping  package ="com.zzn.hibernate.model" >

     < class  name ="Person"  table ="person" >
         < id  name ="id"  column ="id" >
             < generator  class ="identity"   />
         </ id >
         < discriminator  column ="personType"  type ="java.lang.String"   />     <!--  指定描述符对应的列明，注意discrimination标签只能紧跟在id标签后面  -->
        
         < property  name ="name"  type ="java.lang.String"   />                  <!--  公用的name属性，被两个sbuclass标签所用  -->
         < property  name ="age"  type ="java.lang.Integer"   />                  <!--  公用的age属性，被两个sbuclass标签所用  -->
        
         < subclass  name ="Student"  discriminator-value ="student" >              <!--  映射子类Student，描述符是student，此时已经映射Student类，所以不必再写Student.hbm.xml  -->
             < property  name ="cardId"  type ="java.lang.String"   />              <!--  Student私有的属性  -->
         </ subclass >
         < subclass  name ="Teacher"  discriminator-value ="teacher"   >
             < property  name ="salary"  type ="java.lang.Integer"   />              <!--  Teacher私有的属性  -->
         </ subclass >
            
     </ class >
    
</ hibernate-mapping >

一个类对应一张表

<? xml version="1.0" encoding='gb2312' ?>   
<! DOCTYPE hibernate-mapping PUBLIC  
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >   
     
< hibernate-mapping  package ="com.zzn.hibernate.model" >

     < class  name ="Person"  table ="person" >
         < id  name ="id"  column ="id" >
             < generator  class ="identity"   />
         </ id >
         < property  name ="name"  type ="java.lang.String"   />                 
         < property  name ="age"  type ="java.lang.Integer"   />
         < joined-subclass  name ="Student"  table ="student" >
             < key  column ="id"   />
             < property  name ="cardId"  type ="java.lang.String"   />
         </ joined-subclass >
        
         < joined-subclass  name ="Teacher"  table ="teacher" >
             < key  column ="id" />
             < property  name ="salary"  type ="java.lang.Integer"   />
         </ joined-subclass >
     </ class >
    
</ hibernate-mapping >

hibernate.hbm.xml

<? xml version='1.0' encoding='UTF-8' ?>
<! DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd" >
< hibernate-configuration >
     < session-factory >
         < property  name ="show_sql" > true </ property >
         < property  name ="hibernate.hbm2ddl.auto" > update </ property >
         < property  name ="connection.username" > sa </ property >
         < property  name ="connection.password" ></ property >
         < property  name ="connection.url" > jdbc:jtds:sqlserver://localhost:1433;databasename=hibernate_test </ property >
         < property  name ="dialect" > org.hibernate.dialect.SQLServerDialect </ property >
         < property  name ="myeclipse.connection.profile" > SQL2005 </ property >
         < property  name ="connection.driver_class" > net.sourceforge.jtds.jdbc.Driver </ property >
         < mapping  resource ="com/zzn/hibernate/model/Person.hbm.xml" />
     </ session-factory >
</ hibernate-configuration >

测试文件SubclassTest.java

package  com.zzn.hibernate.test;

import  java.util.Iterator;

import  org.hibernate.Query;
import  org.hibernate.Session;
import  org.hibernate.SessionFactory;
import  org.hibernate.Transaction;
import  org.hibernate.cfg.Configuration;

import  com.zzn.hibernate.model.Person;
import  com.zzn.hibernate.model.Student;
import  com.zzn.hibernate.model.Teacher;

public   class  SubClassTest {
     public   static   void  main(String[] args) {
        add();
        select();
    }

     public   static   void  add() {
        Configuration configuration  =   null ;
        SessionFactory sessionFactory  =   null ;
        Session session  =   null ;
        Transaction transaction  =   null ;
        Student student  =   new  Student();
        Teacher teacher  =   new  Teacher();
         try  {
            configuration  =   new  Configuration();
            sessionFactory  =  configuration.configure().buildSessionFactory();
            session  =  sessionFactory.openSession();
            transaction  =  session.beginTransaction();
            student.setName( " shanshan " );
            student.setAge( 25 );
            student.setCardId( " 123456 " );
            teacher.setName( " xiaolan " );
            teacher.setAge( 25 );
            teacher.setSalary( 5000 );
            session.save(student);
            session.save(teacher);
        }  finally  {
             if  (session  !=   null ) {
                transaction.commit();
                session.close();
            }
        }
    }
    
     public   static   void  select(){
        Configuration configuration  =   null ;
        SessionFactory sessionFactory  =   null ;
        Session session  =   null ;
         try  {
            configuration  =   new  Configuration();
            sessionFactory  =  configuration.configure().buildSessionFactory();
            session  =  sessionFactory.openSession();
            Query query  =  session.createQuery( " from Person " );
            Iterator iterator  =  query.list().iterator();
             while  (iterator.hasNext()){
                Person person  =  (Person)iterator.next();
                System.out.println(person.getName());
            }
        }  finally  {
             if  (session  !=   null ) {
                session.close();
            }
        }
    }
}