Hibernate级联操作Cascade学之---save-update

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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

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">

<hibernate-configuration>

<session-factory>

jdbc:mysql://localhost:3306/schoolproject?characterEncoding=gb2312&useUnicode=true

</property>

org.hibernate.dialect.MySQLDialect

</property>

<property name="myeclipse.connection.profile">mysql</property>

com.mysql.jdbc.Driver

</property>

org.hibernate.dialect.MySQLDialect

</property>

<property name="current_session_context_class">thread</property>

</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>

</id>

<many-to-one name="team"

column="team_id"

class="Cascade.saveUpdate.Team"

lazy="no-proxy">

</many-to-one>

</class>

</hibernate-mapping>

Team.hbm.xml 这里先配置成cascade="none"

<?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>

</id>

<one-to-many class="Cascade.saveUpdate.Student"/>

</set>

</class>

</hibernate-mapping>

测试代码：

package Cascade.saveUpdate;

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/saveUpdate"+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

Student removeStu=(Student)session.get(Student.class,"1");//获得需要删除的stu对象

team.getStudents().add(newStu); //增加student到team持有的student集合

team.getStudents().remove(removeStu); //删除student到team持有的student集合

t.commit();

}

运行代码，结果如下：

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

Hibernate: select student0_.id as id0_0_, student0_.cardid as cardid0_0_, student0_.name as name0_0_, student0_.age as age0_0_, student0_.team_id as team5_0_0_ from student student0_ where student0_.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=? and id=?
Hibernate: update student set team_id=? where id=?

Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: Cascade.saveUpdate.Student
at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:219)
at org.hibernate.type.EntityType.getIdentifier(EntityType.java:397)
at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:78)
at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:755)
at org.hibernate.persister.collection.AbstractCollectionPersister.insertRows(AbstractCollectionPersister.java:1364)
at org.hibernate.action.CollectionUpdateAction.execute(CollectionUpdateAction.java:56)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:248)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:232)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:142)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at Cascade.saveUpdate.Test.main(Test.java:30)

可以看到红色的异常，提示没有对象引用，是因为我们没有显示的调用session.save(newStu)又没有设置team端的cascade

如果代码改成session.save(newStu); team.getStudents().add(newStu)就不会有任何问题了

下面，我们看下如果运用cascade="save-update"修正上面的错误，首先修改Team.hbm.xml

注意：cascade="saveupdate"和inverse="false"必须同时设置，才能让team维护级联关系，如果inverse="true"(不让Team维护关系，哪cascad设置也不会有任何作用，虽然可以新插入一条学生的记录，但其team_id为null,无法实现引用关系)，如下图数据库表：

<?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>

</id>

<one-to-many class="Cascade.saveUpdate.Student"/>

</set>

</class>

</hibernate-mapping>

重新运行代码：

Hibernate: insert into student (cardid, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: update student set team_id=null where team_id=? and id=?
Hibernate: update student set team_id=? where id=?

可以看到，红色的部分插入了新数据，并使用update更新其team_id字段，维护约束关系

不过，需要主意的是，使用cascade="save-update"删除集合中的数据时候，不能真正的从数据库中删除记录，只是简单的讲其关联约束字段（如team_id）设置为null,被删除的对象还是保留在session缓存中，还是可以通过
removStu.setName("111")改变对象并进行持久化,如果需要使用这种方式删除对象并持久化，可以设置
cascade="all-delete-orphan"