Hibernate级联操作Cascade学之---delete

所在cascade，就是说我在更新一方的时候，可以根据这一方对象之间的关联关系，去对被关联方进行持久化，比如说Team和Student之间的1对多关系，使用cascade,可以在team方维护其持有的student集合时，自动对其新增，修改，删除的student对象进行持久化，而没必要显示的进行session.save(student)操作，cascade="delete"的意思就是说，我在session.delete(team)的时候，可以一并删除其所有的student

数据库脚本：

create table student(id varchar(32) primary key,
                     team_id varchar(32),
                     name varchar(32),
                     cardid varchar(32),
                     age int);

create table team(id varchar(32) primary key,
                  team_id varchar(32),
                  teamname varchar(32));

                         
insert into team values("1","1","team1");
insert into student values("1","1","stu1","20070101",22);
insert into student values("2","1","stu2","20070102",23);

持久化JavaBean

package Cascade.saveUpdate;


public class Student {
  private String id;
  private String cardid;
  private String name;
  private int age;
  private Team team;
public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
public String getCardid() {
    return cardid;
}
public void setCardid(String cardid) {
    this.cardid = cardid;
}
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;
}

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


package Cascade.saveUpdate;


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

public class Team {
   private String id;
   private Set students=new HashSet();
   private String teamName;
public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
public Set getStudents() {
    return students;
}
public void setStudents(Set students) {
    this.students = students;
}
public String getTeamName() {
    return teamName;
}
public void setTeamName(String teamName) {
    this.teamName = teamName;
}


}

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>
    <property name="jdbc.batch_size">15</property>
    <mapping resource="Cascade/delete/Student.hbm.xml" />
    <mapping resource="Cascade/delete/Team.hbm.xml" />



</session-factory>

</hibernate-configuration>

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>
<class name="Cascade.delete.Student" table="student">
  <id name="id" unsaved-value="null">
    <generator class="uuid.hex"></generator>
  </id>
  <property name="cardid" type="string"/>
  <property name="name" type="string"/>
  <property name="age" type="int"/>
  <many-to-one name="team" 
               column="team_id"
               class="Cascade.delete.Team"
               lazy="no-proxy">
  </many-to-one>
</class>

</hibernate-mapping>

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>
<class name="Cascade.delete.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" inverse="false" cascade="delete">
         <key column="team_id"></key>
         <one-to-many class="Cascade.delete.Student"/>
       </set>
      </class>
</hibernate-mapping>

测试代码：

package Cascade.delete;


import java.io.File;

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

public class Test {


    public static void main(String[] args) {

        String filePath=System.getProperty("user.dir")+File.separator+"src/Cascade/delete"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        System.out.println(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Transaction t=session.beginTransaction();
        Student newStu=new Student();  //建立一个student对象，瞬态
        newStu.setCardid("12345");
        newStu.setAge(22);
        newStu.setName("newStu");
        Team team=(Team)session.get(Team.class, "1");//获得team对象
        session.delete(team);//删除team并一并删除其所有拥有的student
        /*
         * 设置cascade="delete" 只能通过session.delete()删除其所有的学生
         * 设置cascade="delete-orphan" 可以通过team.getStudents().remove(stu)方式删除学生
         */
        t.commit();
        
    }

}

运行结果：

Hibernate: select team0_.id as id1_0_, team0_.teamname as teamname1_0_ from team team0_ where team0_.id=?

Hibernate: select students0_.team_id as team5_1_, students0_.id as id1_, students0_.id as id0_0_, students0_.cardid as cardid0_0_, students0_.name as name0_0_, students0_.age as age0_0_, students0_.team_id as team5_0_0_ from student students0_ where students0_.team_id=?

Hibernate: update student set team_id=null where team_id=?
Hibernate: delete from student where id=?
Hibernate: delete from student where id=?
Hibernate: delete from team where id=?

需要注意的是红色部分的update,照说应该只有select和delete操作，这是因为我们再Team方设置inverse="false"|
这就要求Team要维护Team和Student之间的1对多关系，所以Hibernat将Student的team_id设置成null以断开他么之间的联系，其实这个update是多余的，因为修改后还是被删除了，这点可以通过设置inverse="true"来时实现，可以提高一些效率