Hibernate 学生和课程多对多映射关系实现（单向）
Student.java
package com.java1234.model;
import java.util.HashSet;
import java.util.Set;
public class Student {
private int id;
private String name;
private Set<Course> courses=new HashSet<Course>();
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<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
}
Course.java
package com.java1234.model;
public class Course {
private int id;
private String name;
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;
}
}
Course.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.java1234.model">
<class name="Course" table="t_course">
<id name="id" column="courseId">
<generator class="native"></generator>
</id>
<property name="name" column="courseName"></property>
</class>
</hibernate-mapping>
Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.java1234.model">
<class name="Student" table="t_student">
<id name="id" column="studentId">
<generator class="native"></generator>
</id>
<property name="name" column="studentName"></property>
<set name="courses" table="student_course" cascade="save-update">
<key column="student_id"></key>
<many-to-many class="com.java1234.model.Course" column="course_id"></many-to-many>
</set>
</class>
</hibernate-mapping>
解析：建立一张中间表student_course，这个表中的student_id和course_id分别是那两个表的主键
运行之后数据库截图：
Hibernate 学生和课程多对多映射关系实现（多向）
和单向不同之处：
Course2.java
package com.java1234.model;
import java.util.HashSet;
import java.util.Set;
public class Course2 {
private int id;
private String name;
private Set<Student2> students=new HashSet<Student2>();
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<Student2> getStudents() {
return students;
}
public void setStudents(Set<Student2> students) {
this.students = students;
}
}
Course2.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.java1234.model">
<class name="Course2" table="t_course2">
<id name="id" column="courseId">
<generator class="native"></generator>
</id>
<property name="name" column="courseName"></property>
<set name="students" table="student_course2" inverse="true" >
<key column="course_id"></key>
<many-to-many class="com.java1234.model.Student2" column="student_id"></many-to-many>
</set>
</class>
</hibernate-mapping>
Student2.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.java1234.model">
<class name="Course2" table="t_course2">
<id name="id" column="courseId">
<generator class="native"></generator>
</id>
<property name="name" column="courseName"></property>
<set name="students" table="student_course2" inverse="true" >
<key column="course_id"></key>
<many-to-many class="com.java1234.model.Student2" column="student_id"></many-to-many>
</set>
</class>
</hibernate-mapping>
StudentTest.java
package com.java1234.service;
import java.util.Iterator;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.java1234.model.Course;
import com.java1234.model.Course2;
import com.java1234.model.Student;
import com.java1234.model.Student2;
import com.java1234.util.HibernateUtil;
public class StudentTest {
private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
private Session session;
@Before
public void setUp() throws Exception {
session=sessionFactory.openSession(); // 生成一个session
session.beginTransaction(); // 开启事务
}
@After
public void tearDown() throws Exception {
session.getTransaction().commit(); // 提交事务
session.close(); // 关闭session
}
@Test
public void testSave1(){
Course course1=new Course();
course1.setName("语文");
Course course2=new Course();
course2.setName("数学");
Student student1=new Student();
student1.setName("张三");
student1.getCourses().add(course1);
student1.getCourses().add(course2);
Student student2=new Student();
student2.setName("李四");
student2.getCourses().add(course1);
student2.getCourses().add(course2);
session.save(student1);
session.save(student2);
}
@Test
public void testLoad1(){
Student student=(Student)session.get(Student.class, 1);
Set<Course> courses=(Set<Course>)student.getCourses();
Iterator it=courses.iterator();
while(it.hasNext()){
Course c=(Course)it.next();
System.out.println(c.getName());
}
}
@Test
public void testSave2(){
Course2 course1=new Course2();
course1.setName("语文");
Course2 course2=new Course2();
course2.setName("数学");
Student2 student1=new Student2();
student1.setName("张三");
student1.getCourses().add(course1);
student1.getCourses().add(course2);
Student2 student2=new Student2();
student2.setName("李四");
student2.getCourses().add(course1);
student2.getCourses().add(course2);
session.save(student1);
session.save(student2);
}
@Test
public void testLoad2(){
Course2 course=(Course2)session.get(Course2.class, 1);
Set<Student2> students=(Set<Student2>)course.getStudents();
Iterator it=students.iterator();
while(it.hasNext()){
Student2 s=(Student2)it.next();
System.out.println(s.getName());
}
}
}
运行之后生成的数据库表结构和单向的一样