ER

teacher：

student：

中間表：

tea_stu：

多對多：在操作和效能方面都不太理想，一般使用較少實際中最好轉換成一對多的物件模型，hibernate會為我們建立中間錶轉換成兩個一對多。

package domain;

import java.util.HashSet;
import java.util.Set;

public class Student {
	private int id;
	private String name;
	private Set<Teacher> teachers = new HashSet<Teacher>();
	public int getId() {
		return id;
	}
	public void setId(int 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;
	}
	
	
}
 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
  
<hibernate-mapping package="domain">
	<class name="Student" table="`student`">
	  	<id name="id" column="`id`">
	  	  <generator class="native"></generator>
	  	</id>
	  	<property name="name" column="name"/>
	  	<set name="teachers" table="tea_stu">
	  		<key column="student_id"></key>
	  		<many-to-many class="Teacher" column="teacher_id"></many-to-many>
	  	</set>
	  	</class>
	
</hibernate-mapping>

package domain;

import java.util.HashSet;
import java.util.Set;

public class Teacher {
	private int id;
	private String name;
	private Set<Student> students = new HashSet<Student>();
	public int getId() {
		return id;
	}
	public void setId(int 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;
	}
	
}
 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
  
<hibernate-mapping package="domain">
	<class name="Teacher" table="`teacher`">
	  	<id name="id" column="`id`">
	  	  <generator class="native"></generator>
	  	</id>
	  	<property name="name" column="name"/>
	  	<set name="students" table="tea_stu">
	  		<key column="teacher_id"></key>
	  		<many-to-many class="Student" column="student_id"></many-to-many>
	  	</set>
	  	</class>
	
</hibernate-mapping>

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="connection.url">jdbc:mysql:///user</property>
		<property name="connection.username">root</property>
		<property name="connection.password">mysqladmin</property>
		<property name="show_sql">true</property>
		<property name="hbm2ddl.auto">create</property>
		<mapping resource="domain/Student.hbm.xml"/>
		<mapping resource="domain/Teacher.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

測試：

package test;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Transaction;
import org.hibernate.classic.Session;

import dao.HibernateUtil;
import domain.Student;
import domain.Teacher;

public class Many2Many {
	public static void main(String[] args) {
		add();
		query();
	}
	static void add(){
		
		Session session = null;
		Transaction tx = null;
		try {
			Set<Teacher> ts = new HashSet<Teacher>();
			Teacher t1 = new Teacher();
			t1.setName("tracher1");
			ts.add(t1);
			Teacher t2 = new Teacher();
			t2.setName("tracher2");
			ts.add(t2);
			
			Set<Student> ss = new HashSet<Student>();
			Student s1 = new Student();
			s1.setName("student1");
			ss.add(s1);
			Student s2 = new Student();
			s2.setName("student2");
			ss.add(s2);
			
//			t1.setStudents(ss);
//			t2.setStudents(ss);
			
			s1.getTeachers().add(t1);
			s1.getTeachers().add(t2);
			
			s2.setTeachers(ts);
			
			session = (Session) HibernateUtil.getSession();
			tx = session.beginTransaction();
			session.save(t1);
			session.save(t2);
			session.save(s1);
			session.save(s2);
			tx.commit();
			
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			if(session != null){
				session.close();
			}
		}
		
	}

	static void query(){
		Session session = null;
		Transaction tx = null;
		try {
			session = (Session) HibernateUtil.getSession();
			tx = session.beginTransaction();
			Teacher t = (Teacher)session.get(Teacher.class, 1);
			System.out.println("student's size:"+t.getStudents().size());
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			if(session != null){
				session.close();
			}
		}
		}
}