hibernate中one-to-many实例一

参考：http://hi.baidu.com/ohaozy/blog/item/ed486a33bc83cf48ac4b5f75.html

下面是我调试过的代码

通过简单的例子说明这几个关系：

以下测试都是在mysql5下完成，数据库表是由hibernate.cfg.xml里配置了。
one-to-many及many-to-one我以教师和学生的关系举例，一个教师对应多个学生，反过来多个学生对应一个教师。

1. 建类

Teacher.java

package com.sjtu.xw.pojo;import java.util.HashSet;import java.util.Set;public class Teacher {private long id;private String teaName;private Set students = new HashSet();public long getId() {return id;}public void setId(long id) {this.id = id;}public String getTeaName() {return teaName;}public void setTeaName(String teaName) {this.teaName = teaName;}public Set getStudents() {return students;}public void setStudents(Set students) {this.students = students;}public String toString() {return "Teacher:[teacherId=" + this.id + "/tteacherName="+ this.teaName + "]";}} 

Student.java

package com.sjtu.xw.pojo;public class Student {private long id;private String stuName;public long getId() {return id;}public void setId(long id) {this.id = id;}public String getStuName() {return stuName;}public void setStuName(String stuName) {this.stuName = stuName;}public String toString() {return "student:[studentId=" + this.id + "/tstudentName="+ this.stuName + "]";}} 

Student.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.sjtu.xw.pojo"><class name="Student" table="student"><id name="id" column="id"><generator class="native"></generator></id><property name="stuName" column="studentName" length="30" /></class></hibernate-mapping> 

Teacher.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.sjtu.xw.pojo"><class name="Teacher" table="teacher"><id name="id" column="id"><generator class="native"></generator></id><property name="teaName" column="teacherName" length="30" /><set name="students" fetch="join" lazy="false"> <!-- <set name="students"> --><key column="teacherId"></key><!--这里的column="teacherId" 是指明了在student表里有一个teacherId的列名，是指向teacher表的外键--><one-to-many class="Student" /></set></class></hibernate-mapping> 

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> <!-- Database connection settings --> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost:3306/coursems</property> <property name="connection.username">root</property> <property name="connection.password">root</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property> <property name="show_sql">false</property> <mapping resource="com/sjtu/xw/pojo/Student.hbm.xml"/> <mapping resource="com/sjtu/xw/pojo/Teacher.hbm.xml"/> </session-factory></hibernate-configuration> 

HibernateUtil.java

package com.sjtu.xw.util;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class HibernateUtil { private static final SessionFactory sessionFactory = buildSessionFactory(); private static SessionFactory buildSessionFactory() { try { // Create the SessionFactory from hibernate.cfg.xml return new Configuration().configure().buildSessionFactory(); } catch (Throwable ex) { // Make sure you log the exception, as it might be swallowed System.err.println("Initial SessionFactory creation failed." + ex); throw new ExceptionInInitializerError(ex); } } public static SessionFactory getSessionFactory() { return sessionFactory; }} 

Test.java

package com.sjtu.xw.test;import java.util.List;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import com.sjtu.xw.pojo.Student;import com.sjtu.xw.pojo.Teacher;import com.sjtu.xw.util.HibernateUtil;public class Test {public static void main(String[] args){Test test=new Test();//test.addStudent();//test.addTeacher();test.test();}public void addStudent() {Student student = new Student();student.setStuName("student6");SessionFactory sf = HibernateUtil.getSessionFactory();Session session = sf.openSession();Transaction tx = session.beginTransaction();session.save(student);tx.commit();session.close();sf.close();}public void addTeacher() {Student student = new Student();student.setId(3);Teacher teacher = new Teacher();teacher.setTeaName("Teacher1");teacher.getStudents().add(student); // 把id为1的学生添加到教师对象// 保存这个教师的同时会更新student表SessionFactory sf = HibernateUtil.getSessionFactory();Session session = sf.openSession();Transaction tx = session.beginTransaction();session.save(teacher);tx.commit();session.close();sf.close();}public void test() {SessionFactory sf = HibernateUtil.getSessionFactory();Session session = sf.openSession();Transaction tx = session.beginTransaction(); List list = session.createQuery("from Teacher t where t.id=1").list(); //List list = session.createQuery("from Teacher t left join fetch t.students where t.id=1").list(); Teacher t = (Teacher)list.get(0); System.out.println(t);// System.out.println(t.getStudents().iterator().next()); for(int i=0;i<list.size();i++) { Teacher tt = (Teacher)list.get(i); System.out.println(tt);// System.out.println(tt.getStudents().iterator().next()); } /*//未明白什么意思，和session有什么关系呢？ * 上面这句话放在session结束前,student在用到的时候将会自动被查询出来，否则查询语句应改为: * from Teacher t left join fetch t.students where t.id=1 * 或者设置teacher.hbm.xml里的set属性，加上：fetch="join" lazy="false": * <set name="students" fetch="join" lazy="false"> * <key column="teacherId"></key> <one-to-many class="model.Student"/> </set> */tx.commit();session.close();sf.close();}}