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