Hibernate级联配置

1.级联是指两个对象之间的操作联动关系，对一个对象执行了操作之后，对其指定的级联对象也需要执行相同的操作；
2.级联配置通过many-to-one的cascade属性实现；
3.cascade属性有四种取值：
  all：所有操作都执行级联操作；
  none：所有操作都不执行级联操作；
  save-update：保存和更新时执行级联操作；
  delete：删除时执行级联操作；
4.通过级联操作可以解决持久化对象不能直接引用瞬时对象的问题。

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">useName</property>
        <property name="connection.url">url</property>
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
        <property name="myeclipse.connection.profile">...</property>
        <property name="connection.password">pass</property>
        <property name="connection.driver_class">driveclass</property>
        <property name="show_sql">true</property>
        
        <mapping resource="pojo/Group.hbm.xml" />
        <mapping resource="pojo/User.hbm.xml" />       
    </session-factory>
</hibernate-configuration>

Group.java:

package pojo;

public class Group {

    private long id;
    private String name;

    public long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

User.java:

package pojo;

public class User {

    private long id;
    private String username;
    private String password;
    private Group group;

    public Group getGroup() {
        return group;
    }

    public void setGroup(Group group) {
        this.group = group;
    }

    public long getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

Group.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 Persistence Tools
-->
<hibernate-mapping>
    <class name="pojo.Group" table="GROUP" schema="SCOTT">
        <id name="id" type="java.lang.Long">
            <column name="ID" precision="22" scale="0" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="20" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

User.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 Persistence Tools
-->
<hibernate-mapping>
    <class name="pojo.User" table="USER" schema="SCOTT">
        <id name="id" type="java.lang.Long">
            <column name="ID" precision="22" scale="0" />
            <generator class="native" />
        </id>
        <property name="username" type="java.lang.String">
            <column name="USERNAME" length="10" not-null="true" />
        </property>
        <property name="password" type="java.lang.String">
            <column name="PASSWORD" length="10" not-null="true" />
        </property>
        <many-to-one name="group" column="RELATEDGROUP" cascade="all" />
    </class>
</hibernate-mapping>

HibernateSessionFactory.java:

package factory;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

public class HibernateSessionFactory {
   
    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    private  static Configuration configuration = new Configuration();
    private static org.hibernate.SessionFactory sessionFactory;
    private static String configFile = CONFIG_FILE_LOCATION;

    static {
        try {
            configuration.configure(configFile);
            sessionFactory = configuration.buildSessionFactory();
        } catch (Exception e) {
            System.err
                    .println("Error Creating SessionFactory");
            e.printStackTrace();
        }
    }
    private HibernateSessionFactory() {
    }
    
    public static Session getSession() throws HibernateException {
        Session session = (Session) threadLocal.get();

        if (session == null || !session.isOpen()) {
            if (sessionFactory == null) {
                rebuildSessionFactory();
            }
         session = (sessionFactory != null) ? sessionFactory.openSession()
                    : null;
            threadLocal.set(session);
        }

        return session;
    }

        public static void rebuildSessionFactory() {
        try {
            configuration.configure(configFile);
            sessionFactory = configuration.buildSessionFactory();
        } catch (Exception e) {
            System.out
                    .println("Error Creating SessionFactory");
            e.printStackTrace();
        }
    }

        public static void closeSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null) {
            session.close();
        }
    }
   
    public static org.hibernate.SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static void setConfigFile(String configFile) {
        HibernateSessionFactory.configFile = configFile;
        sessionFactory = null;
    }

    public static Configuration getConfiguration() {
        return configuration;
    }

}

ExportToDB.java:

package export;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

public class ExportToDB {
    public static void main(String[] args) {
        Configuration cfg = new Configuration().configure();
        SchemaExport export = new SchemaExport(cfg);
        export.create(true, true);
    }
}

ExportDBAddCascade.java:

package export;

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

import factory.HibernateSessionFactory;
import pojo.Group;
import pojo.User;

public class ExportDBAddCascade {

    public static void main(String[] args) {
        Session session = HibernateSessionFactory.getSession();
        session.beginTransaction();
        
        Group group = new Group();
        group.setName("J2EE Developer");
        
        for (int i = 0; i < 10; i++) {
            User user = new User();
            user.setUsername("name" + i);
            user.setPassword("111");
            user.setGroup(group);
            session.save(user);
        }
        
        session.getTransaction().commit();
        
        HibernateSessionFactory.closeSession();
    }

}