Hibernate实体关系映射(OneToMany单边)——完整实例

单边一对多关系：电子邮件管理

单边一对多关系:指一方有集合属性，包含多个多方，而多的一方没有一方的引用。

比如：用户(一)与电子邮件(多)。一个用户可以有多个电子邮件记录。

目的：通过OneToMany映射，当保存用户信息到用户表tb_person时，也能自动保存该用户的邮件的信息到邮件表tb_email

　　　当删除用户信息时，也自动从数据库删除该用户的邮件的信息

实现效果：

用户：     邮件表：

工程目录：（这里用java EE 6 Libraries，5会报错）

jar包

Hibernate的注解方式可以自动生成数据表，不需要自己建表，只需在xml配置文件设置hbm2ddl.auto为create

代码如下：

1、Person.java(用户实体类)

package com.hibernate.bean;

import java.util.ArrayList;
import java.util.List;  

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinColumns;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;
import javax.persistence.Table;  

@Entity
@Table(name="tb_person")
public class Person {  

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;  

    private String name;
    //一对多配置，并配置列关系
    @OneToMany(fetch=FetchType.LAZY,targetEntity=Email.class,
            cascade={CascadeType.PERSIST,CascadeType.REMOVE,CascadeType.MERGE,CascadeType.REFRESH})
    //指定连接表Email中的person_id外键列，参照当前实体对应表的主键列id
    @JoinColumns(value = { @JoinColumn(name="person_id",referencedColumnName="id") })
    //配置排序方法
    @OrderBy(value="email desc")
    private List<Email> emails=new ArrayList<Email>();  //用户方有邮件方的集合属性，包含多个多方,用泛型<Email>指定Email对象

    public Integer getId() {
        return id;
    }  

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

    public String getName() {
        return name;
    }  

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

    public List<Email> getEmails() {
        return emails;
    }  

    public void setEmails(List<Email> emails) {
        this.emails = emails;
    }  

} 

Person实体类中使用@OneToMany配置一对多关系。fetch配置加载方式(延迟加载FetchType.LAZY或即时加载FetchType.EAGER)。

targetEntity中配置集合属性中的类型， 由于emails属性类型为List<Email>,用泛型指定了集合内为Email对象，因此targetEntity可省略。

cascade配置级联方式，本例配置为PERSIST、REMOVE、MERGE、REFRESH，表示在保存、删除、修改、刷新Person类时，可以通过操作Person类来操作Email类。CascadeType.ALL表示所有类型

2、Email.java(邮件实体类)

package com.hibernate.bean;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;  

@Entity
@Table(name="tb_email")
public class Email {  

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;  

    private String email;

    public Integer getId() {
        return id;
    }

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

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }  

}  

3、HibernateSessionFactory.java

package com.hibernate.bean;

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

/**
 * Configures and provides access to Hibernate sessions, tied to the current
 * thread of execution. Follows the Thread Local Session pattern, see
 * {@link http://hibernate.org/42.html }.
 */
public class HibernateSessionFactory {

    /**
     * Location of hibernate.cfg.xml file. Location should be on the classpath
     * as Hibernate uses #resourceAsStream style lookup for its configuration
     * file. The default classpath location of the hibernate config file is in
     * the default package. Use #setConfigFile() to update the location of the
     * configuration file for the current session.
     */
    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    private static Configuration configuration = new AnnotationConfiguration();
    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() {
    }

    /**
     * Returns the ThreadLocal Session instance. Lazy initialize the
     * <code>SessionFactory</code> if needed.
     *
     * @return Session
     * @throws HibernateException
     */
    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;
    }

    /**
     * Rebuild hibernate session factory
     *
     */
    public static void rebuildSessionFactory() {
        try {
            configuration.configure(configFile);
            sessionFactory = configuration.buildSessionFactory();
        } catch (Exception e) {
            System.err.println("%%%% Error Creating SessionFactory %%%%");
            e.printStackTrace();
        }
    }

    /**
     * Close the single hibernate session instance.
     *
     * @throws HibernateException
     */
    public static void closeSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null) {
            session.close();
        }
    }

    /**
     * return session factory
     *
     */
    public static org.hibernate.SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    /**
     * return session factory
     *
     * session factory will be rebuilded in the next call
     */
    public static void setConfigFile(String configFile) {
        HibernateSessionFactory.configFile = configFile;
        sessionFactory = null;
    }

    /**
     * return hibernate configuration
     *
     */
    public static Configuration getConfiguration() {
        return configuration;
    }

}

4、hibernate.cfg.xml(src目录下)

<?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>
      <property name="show_sql">true</property>
      <property name="format_sql">true</property>
      <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
      <property name="connection.url">jdbc:oracle:thin:@192.168.1.2::orcl</property>
      <property name="connection.username">daym2</property>
      <property name="connection.password">daym2</property>
      <property name="connection.isolation"></property>
       <property name="hbm2ddl.auto">create</property>
       <property name="javax.persistence.validation.mode">none</property>

      <!-- SQL方言，这边设定的是Oracle -->
      <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>

      <property name="current_session_context">thread</property>
      <mapping class="com.hibernate.bean.Cat" />
      <mapping class="com.hibernate.bean.Person" />
      <mapping class="com.hibernate.bean.Email" />
    </session-factory>
</hibernate-configuration>

5、TestPersonEmail.java测试类

package com.hibernate.bean;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.Transaction;

public class TestPersonEmail {

    public static void main(String[] args) {
        Person person=new Person();
        person.setName("Jane");

        Email email=new Email();    //实例化一个Email
        email.setEmail("[e-mail]");//设置Email
        person.getEmails().add(email);    //添加到Person对象中

        email=new Email();    //实例化另一个Email
        email.setEmail("[e-mail]");//设置Email
        person.getEmails().add(email);//添加到Person对象中

        Session session=HibernateSessionFactory.getSession();
        //开启一个事务
        session.beginTransaction();
        session.persist(person);//保存person对象，会自动级联保存Email对象

        List list=session.createQuery("select p from Person p left join fetch p.emails e where e.email like '[e-mail]' ").list();
        for(Person p: (List<Person>)list){
            System.out.println("Person:"+p.getName());
            for(Email e:p.getEmails()){
                System.out.println("\tEmail:"+e.getEmail());
            }
        }
        //session.delete(person);//删除person对象，会自动级联删除属于它的Email记录

        session.getTransaction().commit();
        session.close();
    }
}

6、log4j.properties(src目录下)

log4j.rootLogger=INFO,stdout
log4j.category.org.hibernate.tool.hbn2ddl=DEBUG
log4j.category.org.hibernate.SQL=DEBUG
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%-d{yyyy-MM-dd HH\:mm\:ss,SSS} [%c]-[%p] %m%n