Hibernateday04多对多关系

多对多
O           Student      Course 一个学生有多门课程，一个课程有多个学生
               *      ：   *
关系属性  Set<Course>    Set<Student>

R 如何在数据库中表明多对多的关系，提供第三张表，作为关系表
 t_student           t_course           关系表  t_s_c
   id name   age      id  name  score            s_id   c_id 两列联合唯一
    1 haoren 22       1  java   1                1      1
    2 clam   23       2  c++    1                1      2

M 多对多映射文件 三张表两个外建

 

1.在com.jsu.hb.pojo包中写两个实体类Student.java和Course.java

Student.java

 

package com.jsu.hb.pojo;

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

public class Student {
	private Integer id;
	private String name;
	private Integer age;
	/* 关系属性 */
	private Set<Course> courses = new HashSet<Course>();

	// 提供声明内存关系的工具方法
	public void addCourse(Course c) {
		this.courses.add(c);
		c.getStudents().add(this);
	}

	// 解除关系
	public void removeCourse(Course c) {
		this.courses.remove(c);
		c.getStudents().remove(this);
	}
	//解除所有关系
	public void removeAll(){
		for(Course c:courses){
			c.setStudents(null);
		}
		this.courses.clear();
	}

	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 Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public Set<Course> getCourses() {
		return courses;
	}

	public void setCourses(Set<Course> courses) {
		this.courses = courses;
	}

}

 在Course.java中

package com.jsu.hb.pojo;

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

public class Course {
	private Integer id;
	private String name;
	private Integer score;
	/* 关系属性 */
	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 Integer getScore() {
		return score;
	}

	public void setScore(Integer score) {
		this.score = score;
	}

	public Set<Student> getStudents() {
		return students;
	}

	public void setStudents(Set<Student> students) {
		this.students = students;
	}

}

 2.R 建表

create table g_student(
 t_id integer primary key,
 t_name varchar2(30),
 t_age integer
)

create table g_course(
 t_id integer primary key,
 t_name varchar2(30),
 t_score integer
)
--关系表
 create table g_s_c(
  s_id integer references g_student(t_id),
  c_id integer references g_course(t_id),
  primary key (s_id,c_id) 
 )

 3.M 提供映射的配置文件没m2m.hbm.xml文件

<?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.jsu.hb.pojo">
	<class name="Student" table="g_student">
		<id name="id" column="t_id">
			<generator class="increment"></generator>
		</id>
		<property name="name" column="t_name"></property>
		<property name="age" column="t_age"></property>
		<!-- 配置关系属性  多对多 三张表两个外键 -->
		<set name="courses" table="g_s_c" cascade="save-update" inverse="true">
			<key column="s_id"></key><!-- 由当前对象提供的第一个外键 -->
			<many-to-many class="Course" column="c_id"></many-to-many>
		</set>
	</class>
	<class name="Course" table="g_course">
		<id name="id" column="t_id">
			<generator class="increment"></generator>
		</id>
		<property name="name" column="t_name"></property>
		<property name="score" column="t_score"></property>
		<!-- 配置关系属性  多对多 三张表两个外键 -->
		<set name="students" table="g_s_c" cascade="save-update">
			<key column="c_id"></key><!-- 由当前对象提供的第一个外键 -->
			<many-to-many class="Student" column="s_id"></many-to-many>
		</set>
	</class>

</hibernate-mapping>

 4.在hibernate.cfg.xml文件中对映射文件进行注册

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

<hibernate-configuration>
	<session-factory> 
		<!-- show_sql:是否显示hibernate执行的SQL语句，默认为false -->
		<property name="show_sql">true</property>
		<!-- show_sql:是否显示hibernate执行格式化输出的SQL语句，默认为false -->
		<property name="format_sql">true</property>
		<!-- 配置与数据库连接的参数 -->
		<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
		<property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>
		<property name="connection.username">scott</property>
		<property name="connection.password">tiger</property>
		<!-- 2.自身属性相关的配置
			dialect:方言
			hibernate根据dialect的配置进行特定数据性能方面的调优
		 -->
		<property name="dialect">org.hibernate.dialect.Oracle9iDialect</property>
		<mapping resource="com/jsu/hb/pojo/m2m.hbm.xml"></mapping>
	</session-factory>
</hibernate-configuration>

 5.提供获得Session的配置文件HibernateUtil.java

package com.jsu.hb.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
	private static SessionFactory sf;
	private static ThreadLocal<Session> tl= new ThreadLocal<Session>();
	static{
		try{
				Configuration cfg = new Configuration();
				cfg.configure();
				sf=cfg.buildSessionFactory();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
	public static Session openSession(){
		return sf.openSession();
	}
	public static Session getCurrentSession(){
		Session session = tl.get();//先从储存的线程中查找
		if(session==null){
			session=openSession();
			tl.set(session);
			return session;
		}
		return session;
	}
}

 6.在测试类中TestM2M.java中

package com.jsu.hb.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.jsu.hb.pojo.Course;
import com.jsu.hb.pojo.Student;
import com.jsu.hb.util.HibernateUtil;

public class TestM2M {
	public static Student getStu(){
		Student s = new Student();
		s.setName("leon");
		s.setAge(23);	
		
		Course c1 = new Course();
		c1.setName("java");
		c1.setScore(5);
		
		Course c2 = new Course();
		c2.setName("c++");
		c2.setScore(4);
		
		// 在内存中设定关系
		s.addCourse(c1);
		s.addCourse(c2);
		return s;
	}
	@Test
	public void save(){
		Session session = HibernateUtil.getCurrentSession();
		Transaction tx = session.getTransaction();
		tx.begin();
		session.save(getStu());
		tx.commit();
	}
	@Test
	public void del(){
		Session session = HibernateUtil.getCurrentSession();
		Transaction tx = session.getTransaction();
		tx.begin();
		Student s = (Student)session.get(Student.class, 2);
		s.removeAll();
		session.delete(s);
		//Course c = (Course)session.get(Course.class, 3);
		//session.delete(c);
		tx.commit();
	}
}