Hibernate 关系映射(6) 基于中间表关联的单向1:N

基于中间表关联的单向1:N
单向 1 对 N 关联,注意 和 N:1 是相反的

想象下: 吃大锅饭的时候 ,就是很多人住一个地方,一个房间,一个大炕上

eg:  一个地方有多个人住.或者说 多家人
eg:  每个同学记住老师,比老师记住每个同学简单.
(在 n 的一端进行配置效率高)

N            1
Person   : Address
Student  : Teacher

这个里面放的是
单向N 对 1
包括  
无连接表的 N : 1
有连接表的 N : 1

注意需求 是:
以前N:1 是在N的一端配置，也就是因为多个人记住老师　比较容易
现在要在 1的一端配置,就是让一个老师记住所有同学  (这个老师 记忆力比较好) 所以会有 一个集合 放置 所有同学

种类
FKrelated: 基于外键关联
TBrelated: 基于中间表管理

中间表


Teacher



Student

public class Student {

	private Integer sid;
	private String sno;
	private String name;
	private int age;
//...

}

public class Teacher {

	private Integer tid;
	private String name;
	private int age;
	private Double salary;
	
	private Set<Student> students=new HashSet<Student>();


//....
}

DROP TABLE IF EXISTS mytest.teacher_student;

CREATE TABLE mytest.teacher_student
	(
	teacher_id INT NOT NULL,
	student_id INT NOT NULL,
	PRIMARY KEY (teacher_id, student_id),
	UNIQUE KEY student_id (student_id),
	KEY FK2E2EF2DE482FD2B0 (teacher_id),
	KEY FK2E2EF2DE37948810 (student_id),
	CONSTRAINT FK2E2EF2DE37948810 FOREIGN KEY (student_id) REFERENCES student (SID),
	CONSTRAINT FK2E2EF2DE482FD2B0 FOREIGN KEY (teacher_id) REFERENCES teacher (TID)
	);

DROP TABLE IF EXISTS mytest.teacher;

CREATE TABLE mytest.teacher
	(
	TID    INT NOT NULL,
	NAME   VARCHAR (255),
	AGE    INT,
	SALARY DOUBLE,
	PRIMARY KEY (TID)
	);

	DROP TABLE IF EXISTS mytest.student;

CREATE TABLE mytest.student
	(
	SID  INT NOT NULL,
	SNO  VARCHAR (255),
	NAME VARCHAR (255),
	age  INT,
	PRIMARY KEY (SID)
	);

<hibernate-mapping package="com.sh.study.model.o2n.TBrelated">
	<class name="Teacher" table="TEACHER">
		<id name="tid" type="java.lang.Integer" column="TID">
			<generator class="increment"/>
		</id> 
		<property name="name" type="java.lang.String">
			<column name="NAME" />
		</property>
		<property name="age" type="int">
			<column name="AGE" />
		</property>
		<property name="salary" type="java.lang.Double">
			<column name="SALARY" />
		</property>
	
		<!-- 无连接表的 1:N 
		<set name="students1" cascade="all">
			<key column="tid"/>
			<one-to-many class="Student"/>
		</set>
		 -->
		 
		<!-- 基于连接表的 1:N 注意采用  many-to-many 替换 one-to-many  -->
		<set name="students" table="teacher_student" cascade="all" inverse="false">
			<key column="teacher_id"/>
			<many-to-many column="student_id" class="Student" unique="true"/>
		</set>
		
	</class>
</hibernate-mapping>


<hibernate-mapping package="com.sh.study.model.o2n.TBrelated">
	<class name="Student" table="STUDENT">
		<id name="sid" type="java.lang.Integer" column="SID">
			<generator class="increment"/>
		</id> 
		<property name="sno" type="java.lang.String">
			<column name="SNO" />
		</property>
		<property name="name" type="java.lang.String">
			<column name="NAME" />
		</property>
		<property name="age" type="int">
			<column name="age" />
		</property>
	</class>
</hibernate-mapping>

test class

package com.sh.test.hibernate.o2n.tbrelated;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.junit.Before;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.sh.study.model.o2n.TBrelated.Student;
import com.sh.study.model.o2n.TBrelated.Teacher;

//测试 Hibernate 单向 1:N
public class TestHibrO2N {
	private ApplicationContext act;
	private SessionFactory factory;
	@Before
	public void init(){
		act = new ClassPathXmlApplicationContext("classpath:spring/applicationContext.xml");
		factory= act.getBean("sessionFactory",SessionFactory.class);
	}
	@Test
	public void test1() {
		Session session=factory.getCurrentSession();
		Transaction tx=session.beginTransaction();
		
		Student s1=new Student();
		s1.setName("ann");
		s1.setAge(15);
		s1.setSno("s10121");
		
		
		Student s2=new Student();
		s1.setName("lili");
		s1.setAge(16);
		s1.setSno("s10122");
		
		
		Teacher t1=new Teacher();
		t1.setName("Lukuc");
		t1.setAge(26);
		t1.setSalary(1258.5);
		Set<Student> ss=t1.getStudents();
		ss.add(s1);
		ss.add(s2);
		
		
		//持久化对象
		session.persist(t1);
		//session.flush();
		tx.commit();
	
		//如果不是使用的SessionFactory.getSession()来获得Session。
		//而是使用SessionFactory.getCurrentSession()方法来获得Session时，
		//当事务结束的时候，不管是提交还是回滚事务，hibernate会自动关闭Session的，
		//session.close();
	}
	

}