Hibernate的关系映射多对多

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Hibernate的关系映射多对多

在这里我以学生和老师为例，实现多对多的关系，学生可以有多个老师教，当然老师也可以教多个学生，所以我这里以老师和学生实现多对多的关联。

在多对多关系模型中是无法直接表达两个表之间的多对多关联的。需要一个中间连接表，在中间连接表中用外键关联到两个表中。

Domain层的创建：

建立Teacher实体类:

public class Teacher {

private Integer id;

private String name;

private Set<Student> students;

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;

}

Student实例类的创建

public class Student {

private Integer id;

private String name;

private Set<Teacher> teachers;

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;

}

映射文件的创建：

一、单向多对多

Teacher映射文件：Teacher.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

<class name="Teacher" table="teacher"> //映射持久化类

<id name="id"> //映射对象标识符

</id>

<many-to-many class="Student" column="student_id"/>

</set>

</class>

</hibernate-mapping>

Student映射文件：Student.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

</id>

</class>

</hibernate-mapping>

二、双向多对多：
Teacher映射文件：Teacher.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

<class name="Teacher" table="teacher"> //映射持久化类

<id name="id"> //映射对象标识符

</id>

<many-to-many class="Student" column="student_id"/>

</set>

</class>

</hibernate-mapping>

Student映射文件：Student.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

</id>

<many-to-many class="Teacher" column="teacher_id"/>

</set>

</class>

</hibernate-mapping>

配置文件的代码示例：

<!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">

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="connection.url">jdbc:mysql:///demo</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hibernate.hbm2ddl.auto">update</property>

</session-factory>

</hibernate-configuration>

包的导入：

工具包的编写：

public final class HibernateUtil {

private static SessionFactory sessionFactory;

private HibernateUtil(){

}

static{

Configuration cfg=new Configuration();

cfg.configure();

sessionFactory=cfg.buildSessionFactory();

}

public static SessionFactory getSessionFactory() {

return sessionFactory;

}

public static Session getSession(){

return sessionFactory.openSession();

}

//查找

public static Object get(Class clazz,int id) {

Session session = null;

try {

session = HibernateUtil.getSession();

Object obj=session.get(clazz, id);

return obj;

} finally {

if (session != null) {

session.close();

}

//删除

public static void delete(Object obj){

Session session = null;

Transaction tx = null;

try {

session = HibernateUtil.getSession();

tx = session.beginTransaction();

session.delete(obj);

tx.commit();

} finally {

if (session != null) {

session.close();

}

//更新

public static void update(Object obj) {

Session session = null;

Transaction tx = null;

try {

session = HibernateUtil.getSession();

tx = session.beginTransaction();

session.update(obj);

tx.commit();

} finally {

if (session != null) {

session.close();

}

//添加

public static void addUser1(Object obj) {

Session session = null;

Transaction tx = null;

try {

session = HibernateUtil.getSession();

tx = session.beginTransaction();

session.save(obj);

tx.commit();

} finally {

if (session != null) {

session.close();

}

测试类的实现：

public class ManyToMany {

public static void main(String[] args){

add();

//query(1);

}

static void add(){

Session session=null;

Transaction tx=null;

try{

session=HibernateUtil.getSession();

tx=session.beginTransaction();

Teacher t1=new Teacher();

t1.setName("t1");

Teacher t2=new Teacher();

t2.setName("t2");

Student s1=new Student();

s1.setName("s1");

Student s2=new Student();

s2.setName("s2");

Set<Student> ss=new HashSet<Student>();

ss.add(s1);

ss.add(s2);

t1.setStudents(ss);

t2.setStudents(ss);

/*Set<Teacher> ts=new HashSet<Teacher>();

ts.add(t1);

ts.add(t2);

会报主键重复错误

s1.setTeachers(ts);

s2.setTeachers(ts);*/

session.save(t1);

session.save(t2);

session.save(s1);

session.save(s2);

tx.commit();

}finally{

if(session!=null){

session.close();

}

public static void query(int id){

Session session=null;

try{

session=HibernateUtil.getSession();

/*Teacher t= (Teacher) session.get(Teacher.class, id);

System.out.println("教师姓名："+t.getName());

System.out.println("学生成绩表：");

Iterator<Student> it=t.getStudents().iterator();

while(it.hasNext()){

Student student=it.next();

System.out.println(student.getName()+" ");

}*/

Student s=(Student) session.get(Student.class, id);

System.out.println("学生姓名："+s.getName());

System.out.println("教师表：");

Iterator<Teacher> it=s.getTeachers().iterator();

while(it.hasNext()){

Teacher teacher=it.next();

System.out.println(teacher.getName()+" ");

}

}finally{

if(session!=null){

session.close();

}