Hibernate多对多示例

Hibernate多对多关联会生成一张中间表作为管理关系表

代码结构和使用的jar

 

Student.java(省略get sert方法)

package com.orange.demo;import java.util.HashSet;import java.util.Set;/** * 学生实体 */public class Student {private Integer studentId;private String studentName;private Set<Teacher> teachers = new HashSet<Teacher>();}

Teacher.java

package com.orange.demo;import java.util.HashSet;import java.util.Set;/** * 老师实体 */public class Teacher {private Integer teacherId;private String teacherName;private Set<Student> students = new HashSet<Student>();}

 

Test.java

package com.orange.demo;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;public class Test {private static SessionFactory sessionFactory = null;static{Configuration cfg = new Configuration();cfg.configure("hibernate.cfg.xml");//在src目录下sessionFactory = cfg.buildSessionFactory();}public static void main(String[] args) {try {//save();delete();} catch (Exception e) {e.printStackTrace();}}public static void save() throws Exception {Session session = sessionFactory.openSession();Transaction tx =  session.beginTransaction();Student student1 = new Student();student1.setStudentName("大橙子同学");Student student2 = new Student();student2.setStudentName("二橙子同学");Teacher teacher1 = new Teacher();teacher1.setTeacherName("王老师");Teacher teacher2 = new Teacher();teacher2.setTeacherName("汪老师");//第1种：通过学生维护关联关系  //在Student.hbm.xml需要设置inverse=false//在Teacher.hbm.xml需要设置inverse=truestudent1.getTeachers().add(teacher1);student1.getTeachers().add(teacher2);student2.getTeachers().add(teacher1);student2.getTeachers().add(teacher2);//第2种：通过老师维护关联关系 //在Student.hbm.xml需要设置inverse=true//在Teacher.hbm.xml需要设置inverse=false//teacher1.getStudents().add(student1);//teacher1.getStudents().add(student2);//teacher2.getStudents().add(student1);//teacher2.getStudents().add(student2);session.save(student1);session.save(student2);session.save(teacher1);session.save(teacher2);tx.commit();session.close();}public static void delete() throws Exception{Session session = sessionFactory.openSession();Transaction tx =  session.beginTransaction();//Student.hbm.xml inverse=false可以删除学生，并删除关联关系(关联关系表数据被删掉)，inverse=true时不能删除，删除时会异常Student stu = (Student) session.get(Student.class, 1);session.delete(stu);tx.commit();session.close();}}

 

inverse属性用法
Student.hbm.xml和Teacher.hbm.xml 的inverse都设置false表示都来维护关联关系
所以在save方法中添加关联关系选择一种就可以了，如果选择两种会报错
 
Student.hbm.xml和Teacher.hbm.xml 的inverse都设置true表示都让对方来维护关联关系，但实际上都没有维护
所以在save方法中即使 第1种方法和第2种方法同时使用也没有向关系表插入数据

Student.hbm.xml inverse设置false，Teacher.hbm.xml inverse设置true表示学生来维护关联关系，
在save方法中使用第1种或者第1种和第2种同时使用都能维护关联关系，并且不会报异常，
因为老师端不会维护关联关系，所以这种情况下只用第2种方法是不能维护关联关系。

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.orange.demo"><class name="Student" table="t_student"><id name="studentId" column="studentId"><generator class="native"></generator></id><property name="studentName" column="studentName" type="string"></property><set name="teachers" table="t_teacher_student" inverse="false"><key column="studentId"></key><many-to-many class="Teacher" column="teacherId"/></set></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.orange.demo"><class name="Teacher" table="t_teacher"><id name="teacherId" column="teacherId"><generator class="native"></generator></id><property name="teacherName" column="teacherName" type="string"></property><set name="students" table="t_teacher_student" inverse="true"><key column="teacherId"></key><many-to-many class="Student" column="studentId"/></set></class></hibernate-mapping>

hibernate.cfg.xml

<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory name="foo"><!-- 数据库方言 --> <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property><property name="connection.url">jdbc:mysql://localhost:3306/t1?characterEncoding=UTF-8</property><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.username">root</property><property name="hibernate.connection.password">123456</property><!-- 在控制台打印SQL，但不能打印建表语句 --><property name="hibernate.show_sql">true</property><!-- 打印SQL是否格式化 false：不格式化 --><property name="hibernate.format_sql">false</property><!--自动更新数据库结构 --><property name="hbm2ddl.auto">update</property><mapping resource="com/orange/demo/Student.hbm.xml"/><mapping resource="com/orange/demo/Teacher.hbm.xml"/></session-factory></hibernate-configuration>