manytomany

1.Many-to-Many映射(多对多映射关系)

多对多通常是通过建立一张中间表，然后由任一一个多的一方来维护关联关系.

2.一方:

@ManyToMany(mappedBy="teachers")　　--->　　表示由另一方来进行维护

3另一方:

@ManyToMany　　　--->　ManyToMany指定多对多的关联关系

@JoinTable(name="t_teacher_course",joinColumns={ @JoinColumn(name="stuid")}, inverseJoinColumns={ @JoinColumn(name = "tid") })　　--->　　因为多对多之间会通过一张中间表来维护两表直接的关系，所以通过 JoinTable 这个注解来声明，name就是指定了中间表的名字，JoinColumns是一个 @JoinColumn类型的数组，表示的是我这方在对方中的外键名称，inverseJoinColumns也是一个 @JoinColumn类型的数组，表示的是对方在我这放中的外键名称.

（1）这是hibernate.cfg.xml中的内容

<!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>
	    <!-- 显示sql语句 -->
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>   <!-- 启动 -->
		<property name="show_sql">true</property>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><!-- 获得链接-->
		 <!--test是数据库的名字       characterEncoding=utf-8是语言    -->
		<property name="hibernate.connection.url">jdbc:mysql:///test?characterEncoding=utf-8</property>
		<property name="hibernate.connection.username">root</property>  <!-- 用户名 -->
		<property name="hibernate.connection.password"></property> <!-- 密码 -->
		<!--实体类配置文件的路径  -->
		<mapping resource="pojo/Person.hbm.xml"/>
		
	</session-factory>
</hibernate-configuration>

（2）创建pojo对象，并在同一个包中创建对应的配置文件，命名为pojo名称

package com.oracle.pojo;

import java.util.List;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="student")
public class Student {
	@Id
	private int stuId;
	private String stuName;
	@ManyToMany
	@JoinTable(name="student_teacher",joinColumns={@JoinColumn(name="tid")},inverseJoinColumns={@JoinColumn(name="stuid")})
	
	private  List<Teacher>	teachers;
	public Student() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Student(int stuId, String stuName) {
		super();
		this.stuId = stuId;
		this.stuName = stuName;
		
	}
	public int getStuId() {
		return stuId;
	}
	public void setStuId(int stuId) {
		this.stuId = stuId;
	}
	public String getStuName() {
		return stuName;
	}
	public void setStuName(String stuName) {
		this.stuName = stuName;
	}
	public List<Teacher> getTeachers() {
		return teachers;
	}
	public void setTeachers(List<Teacher> teachers) {
		this.teachers = teachers;
	}
	@Override
	public String toString() {
		return "Student [stuId=" + stuId + ", stuName=" + stuName +  "]";
	}
	

}

package com.oracle.pojo;

import java.util.List;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="teacher")
public class Teacher {
	@Id
	private int tId;
	private String tName;
	@ManyToMany(mappedBy="teachers")
	private  List<Student>	students;
	public int gettId() {
		return tId;
	}
	public void settId(int tId) {
		this.tId = tId;
	}
	public String gettName() {
		return tName;
	}
	public void settName(String tName) {
		this.tName = tName;
	}
	public List<Student> getStudents() {
		return students;
	}
	public void setStudents(List<Student> students) {
		this.students = students;
	}
	public Teacher(int tId, String tName) {
		super();
		this.tId = tId;
		this.tName = tName;
		
	}
	public Teacher() {
		super();
		// TODO Auto-generated constructor stub
	}
	@Override
	public String toString() {
		return "Teacher [tId=" + tId + ", tName=" + tName + ", students=" + students + "]";
	}
	
}

增加

package com.oracle.teat;

import java.util.ArrayList;
import java.util.List;

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

import com.oracle.pojo.Student;
import com.oracle.pojo.Teacher;
import com.oracle.until.Until;
public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session session=Until.getSession();
		Transaction transaction=session.beginTransaction();
		Teacher teacher  = new Teacher(101, "王老师");
		Teacher teacher2  = new Teacher(102, "数学老师");
		Student student1= new  Student(2001, "张三");
		Student student2= new  Student(2002, "李四");
		Student student3= new  Student(2003, "王力宏");
		Student student4= new  Student(2004, "赵四");
		Student student5= new  Student(2005, "刘能");
		Student student6= new  Student(2006, "谢广坤");
		List<Teacher> teachers = new ArrayList<>();
		teachers.add(teacher);
		teachers.add(teacher2);
		student1.setTeachers(teachers);
		student2.setTeachers(teachers);
		student3.setTeachers(teachers);
		student4.setTeachers(teachers);
		student5.setTeachers(teachers);
		student6.setTeachers(teachers);
			
		//保存老师
		session.save(teacher);
		session.save(teacher2);
		//保存学生
		session.save(student1);
		session.save(student2);
		session.save(student3);
		session.save(student4);
		session.save(student5);
		session.save(student6);
	

		transaction.commit();
		Until.closeSession();
		
	}

}

查询

package com.oracle.teat;

import java.util.ArrayList;
import java.util.List;

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

import com.oracle.pojo.Student;
import com.oracle.pojo.Teacher;
import com.oracle.until.Until;
public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session session=Until.getSession();
		Transaction transaction=session.beginTransaction();
		
	
	Teacher teacher=	session.load(Teacher.class, 101);
		System.out.println(teacher);
		transaction.commit();
		Until.closeSession();
		
	}

}