Hibernate级联操作学习之持久化临时对象

  在实际程序开发中，经常需要持久化临时对象，比如新建一个学生，将加入到一个存在的班级中（或者新建的一个班级），在这里不妨把引起级联操作的对象称为根对象（本文中所指的就是team对象） ，而根对象可能出于transient,persistence,detach三态，下面分别讨论

首先，建立数据库表：

 

CREATE   TABLE  certificate (
  id  varchar ( 100 )  NOT   NULL   default   '' ,
  description  varchar ( 100 )  default   '' ,
   PRIMARY   KEY   (id)
);





CREATE   TABLE  student (
  team_id  varchar ( 100 )  default   '' ,
  id  varchar ( 100 )  NOT   NULL   default   '' ,
  name  varchar ( 20 )  default   '' ,
  cardId  varchar ( 20 )  NOT   NULL   default   '' ,
  age  int ( 11 )  default   ' 0 ' ,
   PRIMARY   KEY   (id)
);






CREATE   TABLE  team (
  id  varchar ( 100 )  NOT   NULL   default   '' ,
  teamName  varchar ( 100 )  default   '' ,
   PRIMARY   KEY   (id)
);



INSERT   INTO  certificate  VALUES  ( ' 1 ' , ' 110108 ' );
INSERT   INTO  certificate  VALUES  ( ' 2 ' , ' 110109 ' );

INSERT   INTO  student  VALUES  ( ' 1 ' , ' 1 ' , ' tomclus ' , ' 2006m ' , 33 );
INSERT   INTO  student  VALUES  ( ' 2 ' , ' 2 ' , ' tom ' , ' 2007m ' , 22 );
INSERT   INTO  team  VALUES  ( ' 1 ' , ' team1 ' );

 

持久化对象Pojo

 

package  Cascade.Relation;

public   class  Certificate  ... {
    private String id;
    private String description;
    private Student stu;

    public Student getStu() ...{
        return stu;
    }

    public void setStu(Student stu) ...{
        this.stu = stu;
    }


    public String getDescription() ...{
        return description;
    }

    public void setDescription(String description) ...{
        this.description = description;
    }

    public String getId() ...{
        return id;
    }

    public void setId(String id) ...{
        this.id = id;
    }
}


package  Cascade.Relation;

public   class  Student  ... {
    private String id; //标识id
    private String cardId; //学号
    private String name; //学生姓名
    private int age; //岁数
    private Certificate cer;//身分证
    private Team team;//班级


     public int getAge() ...{
        return age;
    }

    public String getName() ...{
        return name;
    }

    public String getCardId() ...{
        return cardId;
    }

    public void setId(String id) ...{
        this.id = id;
    }

    public void setAge(int age) ...{
        this.age = age;
    }

    public void setName(String stuName) ...{
        this.name = stuName;
    }

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

    public String getId() ...{
        return id;
    }

    public Student() ...{ //无参的构造函数
    }

     public Certificate getCer() ...{
        return cer;
    }
    public void setCer(Certificate pass) ...{
        this.cer = pass;
    }

    public Team getTeam() ...{
        return team;
    }

    public void setTeam(Team team) ...{
        this.team = team;
    }
}



package  Cascade.Relation;

import  java.util.HashSet;
import  java.util.Set;


public   class  Team  ... {
    private String id;
    private Set students=new HashSet();
    private String teamName;
    private Set tests;
  
    public Set getTests() ...{
        return tests;
    }
 
    public void setTests(Set tests) ...{
        this.tests = tests;
    }

    public String getId() ...{
        return id;
    }

    public void setId(String id) ...{
        this.id = id;
    }

    public String getTeamName() ...{
        return teamName;
    }

    public void setTeamName(String name) ...{
        this.teamName = name;
    }

    public Set getStudents() ...{
        return students;
    }

    public void setStudents(Set students) ...{
        this.students = students;
    }


}

 

Hibernate.cfg.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" >

<!--  Generated by MyEclipse Hibernate Tools.                    -->
< hibernate-configuration >

< session-factory >
     < property  name ="connection.username" > root </ property >
     < property  name ="connection.url" >
        jdbc:mysql://localhost:3306/schoolproject?characterEncoding=gb2312 &amp; useUnicode=true
     </ property >
     < property  name ="dialect" >
        org.hibernate.dialect.MySQLDialect
     </ property >
     < property  name ="myeclipse.connection.profile" > mysql </ property >
     < property  name ="connection.password" > 1234 </ property >
     < property  name ="connection.driver_class" >
        com.mysql.jdbc.Driver
     </ property >
     < property  name ="hibernate.dialect" >
        org.hibernate.dialect.MySQLDialect
     </ property >
     < property  name ="hibernate.show_sql" > true </ property >
     < property  name ="current_session_context_class" > thread </ property >
     < mapping  resource ="Cascade/Relation/Certificate.hbm.xml"   />
     < mapping  resource ="Cascade/Relation/Student.hbm.xml"   />
     < mapping  resource ="Cascade/Relation/Team.hbm.xml"   />

</ session-factory >

</ hibernate-configuration >

 

HBM配置文件，其中Team到Student是cascade="save-update",Student到Certificate是cascade="all"

Team.hbm.xml

 

<? xml version="1.0" encoding="utf-8" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<!--  
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
< hibernate-mapping  package ="Cascade.Relation"   >
     < class  name ="Cascade.Relation.Team"  table ="team"  lazy ="true" >
        < id  name ="id"  column ="id" >
          < generator  class ="uuid.hex" ></ generator >
        </ id >
        < property  name ="teamName"  column ="teamName" ></ property >
       
        < set  name ="students"  lazy ="true"  
            cascade ="save-update"
            inverse ="false" >
          < key  column ="team_id" ></ key >
          < one-to-many  class ="Cascade.Relation.Student" />
        </ set >
       </ class >
</ hibernate-mapping >

 

Student.hbm.xml

 

<? xml version="1.0" encoding="utf-8" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<!--  
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
< hibernate-mapping  package ="Cascade.Relation"   >
   
     < class  name ="Cascade.Relation.Student"  table ="student"  lazy ="true" >
        < id  name ="id"  column ="id"  unsaved-value ="null" >
          < generator  class ="uuid.hex" ></ generator >
        </ id >

        < property  name ="cardId"  column ="cardId" ></ property >
        < property  name ="name"  column ="name" ></ property >
        < property  name ="age"  column ="age" ></ property >
        <!-- 推荐1对多，多对多使用延迟加载，而多1对1，多对1采用预先抓取 -->
        < one-to-one  name ="cer"  
                   class ="Cascade.Relation.Certificate"
                   constrained ="true"  
                   fetch ="join"  
                   cascade ="all" >
        </ one-to-one >
      
       <!-- 推荐1对多，多对多使用延迟加载，而多1对1，多对1采用预先抓取 -->
        < many-to-one  name ="team"  
                    column ="team_id"
                    fetch ="select"
                    cascade ="none"
                    class ="Cascade.Relation.Team" ></ many-to-one >
       </ class >
</ hibernate-mapping >

 

Certificate.hbm.xml

 

<? xml version="1.0" encoding="utf-8" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<!--  
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
< hibernate-mapping  package ="Cascade.Relation"   >  
     < class  name ="Cascade.Relation.Certificate"  table ="certificate"  lazy ="false" >
        <!--  共享主键关联，在子方配置constrained=true  -->
        < id  name ="id"  column ="id" >
          < generator  class ="foreign" >
            < param  name ="property" > stu </ param >
          </ generator >
        </ id >


        < property  name ="description"  column ="description" ></ property >
        <!-- 推荐1对多，多对多使用延迟加载，而多1对1，多对1采用预先抓取 -->
        < one-to-one  name ="stu"  
                   class ="Cascade.Relation.Student"
                   fetch ="join"
                   cascade ="none"  
                   constrained ="true" >
        </ one-to-one >
       </ class >
</ hibernate-mapping >

 

（1）根对象为瞬态

         测试程序：

                

package  Cascade.Relation;

import  java.io.File;
import  java.io.FileInputStream;

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

public   class  TestTransient  ... {


    public static void main(String[] args) ...{
        String filePath=System.getProperty("user.dir")+File.separator+"src/Cascade/Relation"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Transaction t=session.beginTransaction();
        /**//*
         * 发起级联的team为瞬态，team对student级联更新，student对certificate级联更新
         */
        //新建学生
        Student stu=new Student();
        stu.setName("gao");
        stu.setCardId("12345678");
        stu.setAge(27);
        
        //新建班级
        Team team=new Team();
        team.setTeamName("981");
        
        //新建身份证
        Certificate cer=new Certificate();
        cer.setDescription("idcard");
        
        //设置team和student的关联关系
        stu.setTeam(team);
        team.getStudents().add(stu);
        //设置Student和Certificate的关联关系
        stu.setCer(cer);
        cer.setStu(stu);
        
        session.save(team);    
        t.commit();

    }

}

 

结果：

Hibernate: insert into team (teamName, id) values (?, ?)
Hibernate: insert into certificate (description, id) values (?, ?)
Hibernate: insert into student (cardId, name, age, team_id, id) values (?, ?, ?, ?, ?)

可以看到，保存team同时，也保存的student及certificte

（2）根对象为持久态

         测试程序：

 

package  Cascade.Relation;

import  java.io.File;
import  java.io.FileInputStream;

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

public   class  TestPersistence  ... {


    public static void main(String[] args) ...{
        String filePath=System.getProperty("user.dir")+File.separator+"src/Cascade/Relation"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Transaction t=session.beginTransaction();
        /**//*
         * 发起级联的team为持久态，team对student级联更新，student对certificate级联更新
         */
        //新建学生
        Student stu=new Student();
        stu.setName("gao");
        stu.setCardId("12345678");
        stu.setAge(27);
        

        
        //新建身份证
        Certificate cer=new Certificate();
        cer.setDescription("idcard");
        

        //设置Student和Certificate的关联关系
        stu.setCer(cer);
        cer.setStu(stu);
        
        
        //读取Team
        Team team=(Team)session.get(Team.class, "1");
        team.getStudents().add(stu);//设置team和student关系
        session.save(team);    
        t.commit();

    }

}

 

结果：

Hibernate: select team0_.id as id2_0_, team0_.teamName as teamName2_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team5_3_, students0_.id as id3_, students0_.id as id1_2_, students0_.cardId as cardId1_2_, students0_.name as name1_2_, students0_.age as age1_2_, students0_.team_id as team5_1_2_, certificat1_.id as id0_0_, certificat1_.description as descript2_0_0_, student2_.id as id1_1_, student2_.cardId as cardId1_1_, student2_.name as name1_1_, student2_.age as age1_1_, student2_.team_id as team5_1_1_ from student students0_ inner join certificate certificat1_ on students0_.id=certificat1_.id left outer join student student2_ on certificat1_.id=student2_.id where students0_.team_id=?

Hibernate: insert into certificate (description, id) values (?, ?)
Hibernate: insert into student (cardId, name, age, team_id, id) values (?, ?, ?, ?, ?)

可以看到，前两个sql是读取team及fetch,然后保存certificate和student

 

（3）根对象是游离态

            测试程序：

               

package  Cascade.Relation;

import  java.io.File;
import  java.io.FileInputStream;

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

public   class  TestDetach  ... {


    public static void main(String[] args) ...{
        String filePath=System.getProperty("user.dir")+File.separator+"src/Cascade/Relation"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Session session2=sessionFactory.openSession();
        Transaction t=session.beginTransaction();
        
        /**//*
         * 发起级联的team为游离态，team对student级联更新，student对certificate级联更新
         */
        //新建学生
        Student stu=new Student();
        stu.setName("gao");
        stu.setCardId("12345678");
        stu.setAge(27);
        

        
        //新建身份证
        Certificate cer=new Certificate();
        cer.setDescription("idcard");
        

        //设置Student和Certificate的关联关系
        stu.setCer(cer);
        cer.setStu(stu);
        
        
        //读取Team
        Team team=(Team)session.get(Team.class, "1");

        t.commit();
        session.close();//读取完后关闭session,team变成游离态
        
        Transaction t2=session2.beginTransaction();
        team.getStudents().add(stu);//设置team和student关系
        session2.update(team);//用另一个session重新激活team为持久太
        t2.commit();

    }

}

     运行结果会出现异常如下：

xception in thread "main" org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: Cascade.Relation.Team.students, no session or session was closed

这是因为，我们Team对Student是延迟加载，读取Team后，session关闭，重新把team通过另一个session2变成持久后，team.getStudent()是取不到任何东西的，因为其student集合没有得到初始化，所以我们企图用team.getStudent().add(student)的方式级联保存student是不行的，解决方式很简单，讲Team.hbm.xml中Team对Student的lazy=true 改成lazy=false 结果如下：

Hibernate: select team0_.id as id2_0_, team0_.teamName as teamName2_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team5_3_, students0_.id as id3_, students0_.id as id1_2_, students0_.cardId as cardId1_2_, students0_.name as name1_2_, students0_.age as age1_2_, students0_.team_id as team5_1_2_, certificat1_.id as id0_0_, certificat1_.description as descript2_0_0_, student2_.id as id1_1_, student2_.cardId as cardId1_1_, student2_.name as name1_1_, student2_.age as age1_1_, student2_.team_id as team5_1_1_ from student students0_ inner join certificate certificat1_ on students0_.id=certificat1_.id left outer join student student2_ on certificat1_.id=student2_.id where students0_.team_id=?

Hibernate: insert into certificate (description, id) values (?, ?)
Hibernate: insert into student (cardId, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: update team set teamName=? where id=?
Hibernate: update student set cardId=?, name=?, age=?, team_id=? where id=?
Hibernate: update certificate set description=? where id=?
Hibernate: update student set team_id=? where id=?

主意红色的三条SQL,如果我们脱管根对象没有发生过任何改变，则这些update是没有意义的，我们可以在hbm配置文件中的class级别加上select-before-update="true" 在运行update之前先吧数据库中的数据和脱管对象进行比较，如果不同，再进行更新，如下：

Hibernate: select team0_.id as id2_0_, team0_.teamName as teamName2_0_ from team team0_ where team0_.id=?

Hibernate: select students0_.team_id as team5_3_, students0_.id as id3_, students0_.id as id1_2_, students0_.cardId as cardId1_2_, students0_.name as name1_2_, students0_.age as age1_2_, students0_.team_id as team5_1_2_, certificat1_.id as id0_0_, certificat1_.description as descript2_0_0_, student2_.id as id1_1_, student2_.cardId as cardId1_1_, student2_.name as name1_1_, student2_.age as age1_1_, student2_.team_id as team5_1_1_ from student students0_ inner join certificate certificat1_ on students0_.id=certificat1_.id left outer join student student2_ on certificat1_.id=student2_.id where students0_.team_id=?

Hibernate: select team_.id, team_.teamName as teamName2_ from team team_ where team_.id=?
Hibernate: select student_.id, student_.cardId as cardId1_, student_.name as name1_, student_.age as age1_, student_.team_id as team5_1_ from student student_ where student_.id=?
Hibernate: select certificat_.id, certificat_.description as descript2_0_ from certificate certificat_ where certificat_.id=?

Hibernate: insert into certificate (description, id) values (?, ?)
Hibernate: insert into student (cardId, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: update student set team_id=? where id=?

这样会多出一些Select SQL,但相比update,效率要高很多