1, table relationships:
There were three tables: curriculum, students table, the score table. Curriculum and student relationship is many to many, since a corresponding number of student courses, and elective courses were more than a student. If many, many to one point of view to look at the relationship between curriculum and student is obviously wrong, because the curriculum and student tables have no foreign keys.
Therefore, in order to find the relationship between the table-many, the need to introduce a third table (score table), the score table contains the primary key curriculum and student tables, the two can not have been associated with a third table by table connect them.
2, Entity Relationship expression:
Two entities were created two set collection of objects stored in the other entity.
3-many configuration:
（1）student.hbm.xml：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Student" table="student">
<id name="studentno" column="studentno" >
<generator class="native"></generator>
</id>
<property name="birthday" column="birthday"></property>
<property name="classno" column="classno"></property>
<property name="email" column="email"></property>
<property name="phone" column="phone"></property>
<property name="sex" column="sex"></property>
<property name="sname" column="sname"></property>
<property name="point" column="point"></property>
<set name="courses" table="score" inverse="true"><!--一对多关系配置-->
<key column="studentno"></key><!--指定了集合表的外键-->
<many-to-many class="Course" column="courseid"></many-to-many>
</set>
</class>
</hibernate-mapping>
前面的内容大多是对主键和普通属性的配置，主要是对于一对多关系的配置：
<set name="courses" table="score" inverse=“true”><!--一对多关系配置--> <key column="studentno"></key><!--指定了集合表的外键--> <many-to-many class="Course" column="courseid"></many-to-many> </set>
name属性：对应的多的一方的集合名字。
table：联系student表和course表关系的第三个表。
column：student表的外键。
class：对应的多的一方（课程）的类名。
column：对应的多的一方的类的主键。
inverse:等于true相当于让学生一方放弃维护关系，因为双方同时维护关系会导致错误。
（2）course.hbm.xml：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Course" table="course">
<id name="courseid" column="courseid" >
<generator class="native"></generator>
</id>
<property name="courseno" column="courseno"></property>
<property name="cname" column="cname"></property>
<property name="credit" column="credit"></property>
<property name="type" column="type"></property>
<property name="period" column="period"></property>
<set name="students" table="score"><!--一对多关系配置-->
<key column="courseid"></key><!--指定了集合表的外键-->
<many-to-many class="Student" column="studentno"></many-to-many>
</set>
</class>
</hibernate-mapping>
（3）虽然联系student表和course表需要第三个表score，但是并不需要对score表进行配置。
4、多对多的基本操作：
（1）学生和课程的多对多添加：
public static void testadd() {
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Student student=new Student();
student.setSname("翟");
student.setPoint(123f);
student.setClassno(46);
student.setSex("男");
student.setBirthday("2019-11-11");
student.setPhone("18739496522");
student.setEmail("[email protected]");
Student student1=new Student();
student1.setSname("翟hb");
student1.setPoint(666f);
student1.setClassno(46);
student1.setSex("女");
student1.setBirthday("2019-11-11");
student1.setPhone("18739496522");
student1.setEmail("[email protected]");
Course course=new Course();
course.setCourseno("123");
course.setCname("算法设计");
course.setType("必修");
course.setCredit(4);
course.setPeriod(22);
Course course1=new Course();
course.setCourseno("456");
course1.setCname("网络");
course1.setCredit(2);
course1.setPeriod(12);
course1.setType("必修");
student.getCourses().add(course);
student.getCourses().add(course1);
student1.getCourses().add(course);
student1.getCourses().add(course1);
session.save(student);
session.save(student1);
session.save(course);
session.save(course1);
transaction.commit();//提交事务
session.close();//关闭资源
}
分别创建了两个学生对象和两个课程对象，在学生类的集合中添加两个课程对象，同样，在课程类的集合中添加两个学生对象，并将他们转换为持久化状态。
运行结果：
学生：
课程：
分数：
（2）为一个学生添加课程：
public static void testadd1(){
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Student student=session.get(Student.class,1);//获得要添加的学生对象
Course course=new Course();//创建课程对象
course.setCname("算法设计");
course.setType("必修");
course.setCredit(4);
course.setPeriod(22);
course.setCourseno("123");
student.getCourses().add(course);
session.save(course);//转化为持久态
transaction.commit();//提交事务
session.close();//关闭资源
}
运行结果：
学生：
课程：
分数：
可以看到学号为1的学生增加了课程id为1的课程。
（2）删除操作：
public static void testDel(){
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Student student=session.get(Student.class,1);//获得要添加的学生对象
Course course=session.get(Course.class,1);
Course course1=session.get(Course.class,2);
student.getCourses().remove(course);
student.getCourses().remove(course1);
transaction.commit();//提交事务
session.close();//关闭资源
}
5、级联操作：
（1）级联保存：
public static void testadd1(){
Session session = HibernateUtils.openSession();//获得session
Transaction transaction = session.beginTransaction();//开启事务
Student student=session.get(Student.class,1);//获得要添加的学生对象
Course course=new Course();//创建课程对象
course.setCname("算法设计");
course.setType("必修");
course.setCredit(4);
course.setPeriod(22);
course.setCourseno("123");
student.getCourses().add(course);
transaction.commit();//提交事务
session.close();//关闭资源
}
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Course" table="course">
<id name="courseid" column="courseid" >
<generator class="native"></generator>
</id>
<property name="courseno" column="courseno"></property>
<property name="cname" column="cname"></property>
<property name="credit" column="credit"></property>
<property name="type" column="type"></property>
<property name="period" column="period"></property>
<set name="students" table="score" cascade="save-update"><!--一对多关系配置-->
<key column="courseid"></key><!--指定了集合表的外键-->
<many-to-many class="Student" column="studentno"></many-to-many>
</set>
</class>
</hibernate-mapping>
与一对多、多对一相似，级联操作的运用可以减少代码量。
（2）级联删除：
可以使用，但是危险系数较高。