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(); } }