Hibernate多对多数据关联

多对多的关联

例如：学生选课，一个学生可以选多门课程，一门课程可以有多个学生

create table student

(

sid int primary key,

sname varchar(20) not null,

age int not null,

)

create table course

(

cid int identity(1,1) primary key,

cname varchar(20) not null,

score int not null,

)

create table studentcourse

(

sid int,

cid int,

constraint FK_CID foreign key(cid) references course(cid),

constraint FK_SID foreign key(sid) references student(sid)

)

建立POJO 类之间的关系

Student.java:

import java.util.*;

public class Student {

private int sid;

private String sname;

private int age;

private Set course=new HashSet(0);

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public Set getCourse() {

return course;

}

public void setCourse(Set course) {

this.course = course;

}

public int getSid() {

return sid;

}

public void setSid(int sid) {

this.sid = sid;

}

public String getSname() {

return sname;

}

public void setSname(String sname) {

this.sname = sname;

}

}

Course.java:

import java.util.*;

public class Course {

private int cid;

private String cname;

private int score;

private Set student=new HashSet(0);

public int getCid() {

return cid;

}

public void setCid(int cid) {

this.cid = cid;

}

public String getCname() {

return cname;

}

public void setCname(String cname) {

this.cname = cname;

}

public int getScore() {

return score;

}

public void setScore(int score) {

this.score = score;

}

public Set getStudent() {

return student;

}

public void setStudent(Set student) {

this.student = student;

}

}


配置映射文件：

Student.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<class name="student.Student" table="student" catalog="myshop" schema="dbo">

<id name="sid" type="java.lang.Integer">

<column name="sid"></column>

<generator class="assigned"></generator>

</id>

<property name="sname" type="java.lang.String">

<column name="sname" length="20" not-null="true"></column>

</property>

<property name="age" type="java.lang.Integer">

<column name="age" length="20" not-null="true"/>

</property>

<!--name表示Student类中Set的名称，多对多使用studentcourse表维护关系 -->

<set name="course" table="studentcourse" cascade="all">

<key>

<!-- 学生表在关系表中的外键 -->

<column name="sid"></column>

</key>

<!--Set集合中每个元素的类型， -->

<many-to-many class="student.Course">

<!-- 在关系表中的外键 -->

<column name="cid"></column>

</many-to-many>

</set>

</class>

</hibernate-mapping>


Course.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<class name="student.Course" table="course" catalog="myshop" schema="dbo">

<id name="cid" type="java.lang.Integer">

<column name="cid"></column>

<generator class="native"></generator>

</id>

<property name="cname" type="java.lang.String">

<column name="cname" length="20" not-null="true"></column>

</property>

<property name="score" type="java.lang.Integer">

<column name="score" not-null="true"/>

</property>

<!-- name 表示Course中Set集合名称，及使用的关系表 -->

<!-- inverse 表示是否有主动权，为true表示没有主动权

如果这里不把inverse设置成false，那么还会插入一条

-->

<set name="student" table="studentcourse" inverse="true">

<key>

<!-- 课程表在关系表中的外键 -->

<column name="cid"></column>

</key>

<!--Set集合中每个元素的类型 -->

<many-to-many class="student.Student">

<!--Student表在关系表中的外键 -->

<column name="sid"></column>

</many-to-many>

</set>

</class>

</hibernate-mapping>


测试类：

import java.util.*;

import org.hibernate.*;

import org.hibernate.cfg.*;

public class Test {

private SessionFactory sessionFactory;

private Session session;

public Test()

{

sessionFactory=new Configuration().configure().buildSessionFactory();

session=sessionFactory.openSession();

}

public void doCreate()

{

Student s1=new Student();

Student s2=new Student();

s1.setSid(3);

s1.setSname("张三");

s1.setAge(20);

s2.setSid(2);

s2.setSname("李四");

s2.setAge(22);

Course c1=new Course();

c1.setCname("JAVA");

c1.setScore(98);

s1.getCourse().add(c1);

s2.getCourse().add(c1);

c1.getStudent().add(s1);

c1.getStudent().add(s2);

session.save(s1);

session.beginTransaction().commit();

session.close();

}


public static void main(String[]args)

{

new Test().doCreate();

}

}

运行结果：

Hibernate: insert into myshop.dbo.student (sname, age, sid) values (?, ?, ?)

Hibernate: insert into myshop.dbo.course (cname, score) values (?, ?)

Hibernate: insert into studentcourse (sid, cid) values (?, ?)

此时，插入的只是第一个学生，如果在插入第二个学生，你会发现课程名称也被插入。这是因为对于Hibernate来说课程是一个新的实体，如果

是新的实体，则肯定会重新插入



public void doCreate()

{

Student s1=new Student();

s1.setSid(4);

s1.setSname("王五");

s1.setAge(20);

Course c1=(Course)session.get(Course.class, 1);

c1.setCname("JAVA");

c1.setScore(98);

s1.getCourse().add(c1);

c1.getStudent().add(s1);

session.save(s1);

session.beginTransaction().commit();

session.close();

}