Hibernate（七）实现多对多关联映射关系

直接以老师与学生的关系为例。在多对多关联关系中，其中一方都可通过Set保留另一方的所有信息，这样的关联是双向关联。在多对多关联关系中，也只能是双向关联。老师和学生分别对应一张表，通过一张有双方id的中间表来维护多对多的关联。

实体类

package test.hibernate.hbmManyToMany;import java.util.HashSet;import java.util.Set;public class Teacher {private Integer id;private String name;private Set<Student> students = new HashSet<Student>();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 Set<Student> getStudents() {return students;}public void setStudents(Set<Student> students) {this.students = students;}@Overridepublic String toString() {// TODO Auto-generated method stubreturn "[Teacher:id=" + id + ",name=" + name + "]";}}

package test.hibernate.hbmManyToMany;import java.util.HashSet;import java.util.Set;public class Student {private Integer id;private String name;private Set<Teacher> teachers = new HashSet<Teacher>();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 Set<Teacher> getTeachers() {return teachers;}public void setTeachers(Set<Teacher> teachers) {this.teachers = teachers;}@Overridepublic String toString() {// TODO Auto-generated method stubreturn "[Student:id=" + id + ",name=" + name + "]";}}

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="test.hibernate.hbmManyToMany"><class name="Student" table="student"><id name="id" type="integer" column="id"><generator class="native" /></id><property name="name" /><!-- inverse属性：默认为false,表示本方维护关联关系; 如果设为true,表示本方不维护关联关系 只是影响是否能设置外键列的值(设成有效值或是null值),对获取信息没有影响 --><set name="teachers" table="teacher_student"><key column="studentId"></key><many-to-many class="Teacher" column="teacherId"></many-to-many></set></class></hibernate-mapping>

在多对多关系中，可在Set里通过inverse设置只有其中一方维护。

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="test.hibernate.hbmManyToMany"><class name="Teacher" table="teacher"><id name="id" type="integer" column="id"><generator class="native" /></id><property name="name" /><set name="students" table="teacher_student"><key column="teacherId"></key><many-to-many class="Student" column="studentId"></many-to-many></set></class></hibernate-mapping>

测试类

package test.hibernate.hbmManyToMany;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import org.junit.Test;public class App {private static SessionFactory sessionFactory = new Configuration()//.configure()//.addClass(Teacher.class)// 添加Hibernate实体类（加载对应的映射文件）.addClass(Student.class)//.buildSessionFactory();@Testpublic void testSave() throws Exception {Session session = sessionFactory.openSession();session.beginTransaction();// --------------------------------------------// 构建对象Teacher teacher1 = new Teacher();teacher1.setName("林老师");Teacher teacher2 = new Teacher();teacher2.setName("张老师");Student student1 = new Student();student1.setName("李明");Student student2 = new Student();student2.setName("刘备");teacher1.getStudents().add(student1);teacher1.getStudents().add(student2);teacher2.getStudents().add(student1);teacher2.getStudents().add(student2);// 下面部分不能与上面的代码块同时进行,只能选择其中一部分,不然会抛出在中间表中重复插入相同记录的异常// 如果两边都要写，注意设置其中一方的inverse为true// student1.getTeachers().add(teacher1);// student1.getTeachers().add(teacher2);// student2.getTeachers().add(teacher1);// student2.getTeachers().add(teacher2);// 保存session.save(teacher1);session.save(teacher2);session.save(student1);session.save(student2);// --------------------------------------------session.getTransaction().commit();session.close();}// 获取到部门关联的员工@Testpublic void testGet() throws Exception {Session session = sessionFactory.openSession();session.beginTransaction();// 获取数据Teacher teacher = (Teacher) session.get(Teacher.class, 4);System.out.println(teacher);System.out.println(teacher.getStudents());session.getTransaction().commit();session.close();}// 解除关联关系@Testpublic void testRemoveRelation() throws Exception {Session session = sessionFactory.openSession();session.beginTransaction();// --------------------------------------------// 如果Teacher.hbm.xml中inverse=false就可以删除，否则不可以删除Teacher teacher = (Teacher) session.get(Teacher.class, 4);teacher.getStudents().clear();// --------------------------------------------session.getTransaction().commit();session.close();}// 删除部门及对员工的影响@Testpublic void testDelete() throws Exception {Session session = sessionFactory.openSession();session.beginTransaction();// --------------------------------------------// 会同时删除teacher_student和teacher中教师id=4的记录Teacher teacher = (Teacher) session.get(Teacher.class, 4);session.delete(teacher);// --------------------------------------------session.getTransaction().commit();session.close();}}

由代码生成的表结构

执行testGet方法时控制台内容

原文出处：http://blog.csdn.net/lindonglian/article/details/46916891