Hibernate总结（五）--之多对多操作

直接演示代码：

Course类 （课程）

public class Course implements Serializable{private Long cid;private String name;private String description;private Set<Student> students;

Student类（学生）

public class Student implements Serializable{private Long sid;private String name;private String description;private Set<Course> courses;

Course.hbm.xml

<hibernate-mapping><class name="com.itheima12.hibernate.domain.Course"><id name="cid" length="5"><generator class="increment"></generator></id><property name="description" length="50"></property><property name="name" length="20"></property><!-- table        第三张表 --><set name="students" table="student_course" cascade="save-update"><key><!-- 外键 --><column name="cid"></column></key><!-- column外键 --><many-to-many class="com.itheima12.hibernate.domain.Student" column="sid"></many-to-many></set></class></hibernate-mapping>

Student.hbm.xml

<hibernate-mapping><class name="com.itheima12.hibernate.domain.Course"><id name="cid" length="5"><generator class="increment"></generator></id><property name="description" length="50"></property><property name="name" length="20"></property><!-- table        第三张表 --><set name="students" table="student_course" cascade="save-update"><key><!-- 外键 --><column name="cid"></column></key><!-- column外键 --><many-to-many class="com.itheima12.hibernate.domain.Student" column="sid"></many-to-many></set></class></hibernate-mapping>

测试代码

public class ManyToManyTest extends HibernateUtils{/** * 保存学生的时候，同时保存课程 * Hibernate:     select        max(sid)     from        StudentHibernate:     select        max(cid)     from        CourseHibernate:     insert     into        Student        (description, name, sid)     values        (?, ?, ?)Hibernate:           在Student.hbm.xml文件中       <set cascade="save-update">    insert     into        Course        (description, name, cid)     values        (?, ?, ?)Hibernate:            建立关系的sql语句    insert     into        student_course        (sid, cid)     values        (?, ?) */@Testpublic void testSaveStudent_Cascade_Save_Course(){Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();Student student = new Student();student.setName("aa");Course course = new Course();course.setName("java基础课程");//建立学生与课程之间的关系Set<Course> courses = new HashSet<Course>();courses.add(course);student.setCourses(courses);session.save(student);transaction.commit();session.close();}/** * 已经存在一个课程，已经存在一个学生，建立该课程和该学生之间的关系 */@Testpublic void testBuildR(){Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();//把cid为2的课程和sid为1的学生提取出来Course course = (Course)session.get(Course.class, 2L);Student student = (Student)session.get(Student.class, 1L);student.getCourses().add(course);transaction.commit();session.close();}/** * 已经存在一个课程，新建一个学生，建立该课程和该学生之间的关系 */@Testpublic void testSaveStudent_BuildR(){Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();Student student = new Student();student.setName("student1");Course course = (Course)session.get(Course.class, 1L);/** * 建立了新的学生与该课程之间的关系 */Set<Course> courses = new HashSet<Course>();courses.add(course);student.setCourses(courses);session.save(student);transaction.commit();session.close();}/** * 一个学生从一门课程转到另外一门课程 */@Testpublic void testTranform(){/** * sid为1的学生从课程2转到课程1 */Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();//提取sid为1的学生Student student = (Student)session.get(Student.class, 1L);//把课程1和课程2提取出来Course course1 = (Course)session.get(Course.class, 1L);Course course2 = (Course)session.get(Course.class, 2L);student.getCourses().remove(course2);//解除sid为1的学生和cid为2的课程student.getCourses().add(course1);//建立sid为1的学生和cid为1的课程transaction.commit();session.close();}/** * 解除一个学生和该学生所学的所有的课程之间的关系 */@Testpublic void testRealseAllR(){/** * 解除sid为1的学生和所有的课程之间的关系 */Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();Student student = (Student)session.get(Student.class, 1L);student.setCourses(null);transaction.commit();session.close();}/** * 解除一个学生和所有的课程之间的关系，再建立一些课程之间的关系 */@Testpublic void testRealseAllRAndBuildR(){Session session = sessionFactory.openSession();Transaction transaction = session.beginTransaction();Student student = (Student)session.get(Student.class, 1L);Set<Course> courses = new HashSet<Course>();Course course = (Course)session.get(Course.class, 3L);courses.add(course);//把原来的student中的courses给覆盖掉了student.setCourses(courses); transaction.commit();session.close();}