Hibernate学习总结：OneToMany单向关联

说明：

一、例子是一个组有许多用户，但一个用户只能属于一个组

二、本次使用的Hibernate版本是hibernate-release-4.3.11.Final.

先写Annotation版本：

实体类：

Group.java：

package com.buaa.hibernate.bean;import java.util.HashSet;import java.util.Set;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="t_group")public class Group {private int id;private String name;private Set<User> users = new HashSet<User>();@OneToMany@JoinColumn(name="groupId") //多的一方加外键public Set<User> getUsers() {return users;}public void setUsers(Set<User> users) {this.users = users;}@Id@GeneratedValuepublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

User.java：

package com.buaa.hibernate.bean;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="t_user")public class User {private int id;private String name;@Id@GeneratedValuepublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

Xml版本：

User.hbm.xml：

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC  "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.buaa.hibernate.bean"><class name="User" table="t_user">    <id name="id"><generator class="native" /></id><property name="name"/></class><class name="Group" table="t_group"><id name="id"><generator class="native" /></id><property name="name"/><set name="users"><key column="groupId"></key><one-to-many class="User" /></set></class></hibernate-mapping>

此处将两个类写在一个配置文件里面了.

下面是Hibernate配置文件：hibernate.cfg.xml：

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-configuration SYSTEM "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>   <session-factory>      <property name="connection.driver_class">com.mysql.jdbc.Driver</property>   <!-- Assume test is the database name -->   <property name="connection.url">jdbc:mysql://localhost/test</property>   <property name="connection.username">root</property>   <property name="connection.password">123456</property>      <property name="dialect">org.hibernate.dialect.MySQLDialect</property>   <property name="show_sql">true</property>      <property name="format_sql">true</property>   <!-- <property name="hbm2ddl.auto">create</property> --><!--  --><mapping resource="com/buaa/hibernate/bean/User.hbm.xml"/> <!-- <mapping class="com.buaa.hibernate.bean.Group"/><mapping class="com.buaa.hibernate.bean.User"/>  --></session-factory></hibernate-configuration>

最后写Junit测试类：

OneToManyTest.java：

package com.buaa.hibernate.bean;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.hibernate.tool.hbm2ddl.SchemaExport;import org.junit.Test;public class OneToManyTest {@Testpublic void test(){User user1 = new User();user1.setName("alvin");User user2 = new User();user2.setName("jack");Set<User> users = new HashSet<User>();users.add(user1);users.add(user2);Group group = new Group();group.setName("A");group.setUsers(users);Configuration configuration = new Configuration().configure();ServiceRegistry service = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();SessionFactory factory = configuration.buildSessionFactory(service);Session session = factory.openSession();session.beginTransaction();session.save(user1);session.save(user2);session.save(group);session.getTransaction().commit();session.close();factory.close();}@Testpublic void SchemaExportTest(){Configuration cfg = new Configuration().configure();//第一个参数是否将sql语句输出到控制台，第二个参数是否在数据库中生成对应的表格new SchemaExport(cfg).create(true,true);}}